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Abstract(10) FullText HTML(2) PDF 3910KB(0)
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For the multiple salient targets scene, as well as a scene in which some areas of the salient target do not contrast significantly with the background area, the resultant saliency map of the existing algorithm is not fine enough or even loses some saliency regions. In this paper, a new significance detection method combined with selective light field refocusing of camera array is proposed. Our method selects the light field dataset and uses multi-viewpoint images of the same scene. First, we perform refocusing rendering combined with super-resolution on the central viewpoint image; Then, on the basis of the graph-based saliency detection method, we propose a propagation model combining global and local smoothness constraints to prevent false label propagation; finally, the obtained coarse saliency map is refined through the objectness image to output the final saliency map. In addition, for the scene that contains multiple salient targets, we can choose to refocus a certain depth layer in the scene, and produce varying degrees of blurring to other depth layers. This enables the salient targets on the depth layer to be detected more accurately and in detail. To a certain extent, the optional saliency detection is realized. Experiments on the 4D light field dataset show that the average mean absolute error between the saliency map and the ground truth obtained by the method proposed in this paper is 0.2128, which is lower than the existing method. The detection result contains more detailed information about the salient target, which improves the above-mentioned shortcomings of the existing salient detection methods.
Abstract(8) FullText HTML(2) PDF 4013KB(0)
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In this paper, a 1064 nm ytterbium-doped fiber laser with main oscillation power amplification (MOPA) was used as the pump source to achieve mid-infrared 3.8 μm MgO: PPLN optical parametric oscillation (OPO) laser output. In the pump source, the distributed feedback laser (DFB) was used as the seed source to realize the modulation of the narrow linewidth of the fiber laser. The linewidth of 2.5 nm was compressed to 0.1 nm, and the maximum output power was 40 W. The mid-infrared 3.8 μm MgO: PPLN OPO laser was researched under different pump linewidths. Finally, when the pump power was 18.1w, the line width was 0.1 nm, the frequency was 1 MHz, and the pulse width was 2 ns, the maximum power of 2.06 W with the wavelength of 3822.5 nm was achieved, the corresponding optical-optical conversion efficiency is 11.38%, and the beam quality is M2 = 2.34.
Abstract(13) FullText HTML(6) PDF 3198KB(1)
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In biological photoacoustic tomography (PAT), the images of initial pressure, optical deposition and optical properties distribution are usually reconstructed from photoacoustic measurements based on the ideal assumption of uniform and stable illumination for simplicity. However, in practical applications, optical attenuation and inhomogeneous distribution of light fluence in tissue usually occur after the imaging target is illuminated by short laser pulses, which results in inaccurate image reconstruction and reduced image quality. This paper summarizes current methods for compensating for errors caused by inhomogeneous and unstable illumination in PAT under non-ideal conditions and discusses the advantages and limits of these methods.
Abstract(11) FullText HTML(2) PDF 2410KB(0)
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The Influence on beam quality β factor of high-energy laser system is analyzed based on two-dimension chirp Z transformation. The effects of sampling number within diffraction limit and beam spot energy loss on beam quality β factor are analyzed. The simulation results based on different sampling numbers indicate that larger sampling number induces higher beam spot diffraction image resolution which is beneficial for more accurate calculation of beam quality β factor. When the sampling number of diffraction limit angle is no less than ten, the measurement error can be limited within 3%. Meanwhile, different wavefront aberrations have different sensitiveness of beam spot energy loss. The beam quality β factor of high order wavefront aberration is larger than the one of low order aberration with the equal energy loss. Especially, the spherical aberration is most sensitive to energy loss, and about 5% energy loss can induce 15% to 30% calculation error of β factor.
Abstract(5) FullText HTML(0) PDF 4776KB(0)
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Surface plasmon polariton is a mode of electromagnetic surface wave that exists on two dielectric cross-sections (usually metal and insulator) with opposite sign of dielectric constant, which can break the diffraction limit. In an appropriate optical waveguide structure composed of metal and dielectric, light can be trapped at the subwavelength scale. Here, we propose an approach that integrates dielectric waveguiding with plasmonicsby finite-element simulation. The hybrid optical waveguide consists of an active ZnO nanowire separated from a metal surface by a nanoscale dielectric gap (10 nm). The coupling between surface plasmonic and waveguide modes allows energy to be stored and propagated in subwavelength dielectric gap. The leaky modes of ZnO nanowire lose part of their energy to the continuum of dielectric layer during propagation. Due to gain guiding, the hybrid electric leaky mode makes it possible to observe leaky-mode lasing. This approach could lead to the true integration of subwavelength lasers based on nanoscale semiconductor-based plasmons and photonics.
Abstract(47) FullText HTML(17) PDF 6955KB(4)
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The ability to detect linearly polarized light is an important index for evaluating polarized photoelectric detectors. Black arsenic phosphorus (b-AsP) is a relatively stable anisotropic material, and is sensitive to linearly polarized light because of its anisotropy inside its planar structure. The material has important application value in polarization detection. This paper introduces a polarization-sensitive photodetector based on AsP/MoS2. Due to the anisotropic light absorption of AsP, effective carrier collection and strong carrier transport capacity of MoS2, as well as the suppression of dark current by a van der Waals heterojunction, the performance of the photodector shows relatively large on/off ratios. Moreover, the photodector has a current optical responsivity of 0.27 A/W and a detectivity of 2×1010 Jones, and more importantly, achieves a dichroic ratio of up to 3.06 at 638 nm. These experimental results show that AsP/MoS2 heterostructures have broad application prospects in the field of polarized photoelectricity detection.
Abstract(30) FullText HTML(8) PDF 5242KB(12)
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Quantum dot Light-Emitting Diodes (QLEDs) are applied to the lighting and display industry for their unique photoelectric characteristics. Their External Quantum Efficiency (EQEs) is quickly meeting commercial requirements while the device’s lifetime is still one of their biggest challenges. The significant factors affecting the lifetime of QLEDs are divided into two aspects including the stability of the functional layer’s materials and charge imbalance. Various strategies for enhancing QLEDs stability are discussed including improving the stability of quantum dots, implementing Charge Transport Layers (CTLs) and promoting charge balance. With the deepening understanding of the degradation mechanism of QLEDs, more stable quantum dots and QLEDs devices have been developed. However, there are still some obstacles to the commercialization of QLEDs. For example, the high toxicity of Cd and the lifetime and efficiency of blue QLEDs are far lower than the corresponding levels of green and red QLEDs. In addition, the stability of QLEDs at high brightness (1000 cd m−2) is usually much shorter, which still limits the development of QLEDs. Therefore, research and development efforts for QLEDs should be further strengthened to overcome these technical obstacles and achieve the future commercialization of QLEDs.
Abstract(198) FullText HTML(63) PDF 3277KB(14)
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Lead Halide Perovskites(LHPs) are promising candidates for next-generation optoelectronic application. However, defect-induced ion migration causes phase degradation in LHP nanocrystals. Therefore, material stability has become an urgent problem that impedes practical applications. In this paper, we aim to study the influence of doping cations on inhibiting the migration of halogen ions in perovskite nanocrystals. Through the measurement of ion migration activation energy and in-situ high-resolution transmission electron microscope technology, the effect of precursor dopants on the stability of LHPs were analyzed. Firstly, we synthesized two types of LHP nanocrystals with high crystal quality using nickel acetylacetonate and nickel bromide as precursor dopants, respectively. Secondly, the optical properties and component elements of the doped samples were analyzed by absorption-fluorescence spectroscopy, X-ray diffraction, X-ray photoelectron diffraction, and transmission electron microscopy. Finally, the ion migration activation energies of various LHP films were measured using temperature-dependent ion conductivity tests, and the influence of the precursor dopants on the stability of as-synthesized doped LHPs was compared with the results from high-resolution electron microscopy. The results showed that the activation energies of the doped CsPbBr3 samples were significantly improved compared to the intrinsic CsPbBr3 sample (0.07 eV), which were determined to be 0.238 eV for nickel acetylacetonate and 0.487 eV for nickel bromide. In addition, the electron irradiation experiments showed that the nickel bromide-doped perovskite nanocrystals exhibited higher structural stability. This is due to the strong bonding of doped Ni2+ to halogen and the synergistic passivation effect of halogen filling vacancy defects. It can be concluded that Ni2+ doping and halogen vacancy filling can effectively inhibit ion migration in halide perovskite nanocrystals.
Abstract(200) FullText HTML(68) PDF 14141KB(46)
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Two-dimensional (2D) materials like graphene have attracted much attention due to their unique structures and exotic properties. With significantly reduced lateral sizes, 2D quantum sheets (2D QSs) are attracting an increasing level of interest. 2D QSs have opportunities for new applications because of their intrinsic characteristics of being 2D materials and having emerging quantum confinement and prominent edge effects. This review focuses on the conceptual interpretation of 2D QSs and the recent progress on their preparation and optical properties. Particular focus is given to the realization and significance of the universal and scalable production of intrinsic 2D QSs. In addition, the photoluminescence of 2D QSs and their applications in nonlinear optics and solid-state light-emitting devices are reviewed. At the end, the perspectives and challenges towards the future development of 2D QSs are discussed.
Abstract(797) FullText HTML(100) PDF 5889KB(50)
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Because of their unique physical properties, the monolayer and few-layer two-dimensional transition metal chalcogenides with atomic-level thickness are expected to play an important role in the next generation of optoelectronic devices. However, defects in two-dimensional materials affect their properties to a great extent. On one hand, defects reduce the fluorescence quantum efficiency, carrier mobility and other important device parameters. On the other hand, the control and utilization of defects have given birth to new techniques such as using single-photon sources. Therefore, it is very important to characterize, understand, handle and control the defects in two-dimensional materials. In this review, the research progress on defects and its related carrier dynamics in two-dimensional transition metal chalcogenides is summarized. This paper aims to sort out the great influence of defects and their related ultrafast dynamics on material performance in two-dimensional transition metal chalcogenides, and to support studies on fundamental physical properties and high-performance optoelectronic devices.
Abstract(65) FullText HTML(36) PDF 5044KB(9)
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In recent years, materials with Circularly Polarized Luminescence (CPL) have received growing attention due to their wide applications in 3D displays, optical storage, optical security, etc. Supramolecular self-assembling is one of the most effective methods to construct CPL active materials, which can assemble different types of molecules into low-dimensional (0D, 1D and 2D) structures with unique functions. This review summarizes the research progress of self-assembled CPL active organic low-dimensional materials from recent years with emphasis on the driving force of supramolecular self-assembly. Firstly, the review systematically summarizes the current design strategies of self-assembled CPL active organic low-dimensional materials. Secondly, it focuses on their performance and applications. Finally, it discusses the future opportunities and challenges of this rapidly developing field.
Abstract(63) FullText HTML(33) PDF 3810KB(6)
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In order to improve the opto-electronic performance and light extraction efficiency of LEDs based on a GaN-on-silicon platform, we proposed an LED device based on GaN-on-silicon with an ultra-thin freestanding membrane. By combining photolithography, deep reactive ion etching and inductively-coupled plasma reactive ion etching, we prepared an LED based on a GaN-on-silicon platform with an ultra-thin freestanding membrane, removing the silicon substrate of light-emitting area and most area of the electrodes, and thinning most of the GaN epitaxial layer. We performed three-dimensional morphology characterization for the LED device and found that the surface of the LED’s membrane is flat and that the membrane’s deformation is minimal. It is proved that the back process can solve the problem of membrane deformation caused by stress release between the GaN epitaxial layer and the silicon substrate. By characterizing the current-voltage and electroluminescence spectrum of the LED and comparing the LEDs with different structures and different light-emitting area sizes, we found that the opto-electronic performance and light output efficiency of the LED with an ultra-thin freestanding membrane are better than that of the common LED, and the change in size of the light-emitting area has a significant effect on the performance of the LED. Compared with the current of common LED, the current of the LED which has an ultra-thin freestanding membrane with 80-μm diameter light-emitting area increased from 4.3 mA to 23.9 mA under 15 V driving voltage. Under 3-mA current, the peak light intensity increased by about 5 times. The light-emitting efficiency of the LED with a 120-μm diameter light-emitting area is improved more perceptibly compared with that of LED with a 80-μm diameter light-emitting area. This research provides more possibilities for the development of high-performance LED devices with an ultra-thin freestanding membrane.
Abstract(34) FullText HTML(13) PDF 3278KB(7)
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In order to reduce the size of spectrometers and make it suitable for military satellites and other fields, we used colloidal quantum dots as filter materials to study the optical properties of CdSe colloidal quantum dot filters. The high-quality CdSe colloidal quantum dots were synthesized by an organic phase reaction method and prepared into CdSe colloidal quantum dots thin film filters after p-phenylenediamine extinction treatment. The Transmission Electron Microscope (TEM) was used to characterize the morphology and particle size of the as-prepared samples. The UV-visible absorption and UV-visible transmittance were measured at different temperatures. The results indicated that the increase in particle size caused both absorption and transmittance to increase for CdSe colloidal quantum dots thin film filters at room temperature. Under a given particle size, the absorption and transmittance of the first exciton absorption peak red shifted with the rise in temperature. The red shift of absorption curve of CdSe colloidal quantum dots thin film filters did not exceed 1nm per 10 K temperature rising and the half-width increased along with the total throughput. In addition, the stability and tunable characteristics of the CdSe colloidal quantum dots thin film filters have been verified through repeated experiments, and it is suitable as a cut-off filter. Therefore, CdSe colloidal quantum dots thin film filters have high value in micro-spectrometers.
Abstract(158) FullText HTML(85) PDF 4709KB(10)
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Zinc sulfide (ZnS) crystal is one of the important materials used to make the wide-spectrum infrared window. The ultrafast laser technology for manufacturing the nanopores with high aspect ratio provides an important approach to fabricate the photonic devices such as mid-infrared waveguide Fourier transform spectrometer etc. In this paper, a 40-times-demagnification ultrafast laser direct-writing system was built with a 4f system and a Gaussian-Bessel beam generated by a quartz axicon and a Yb:KGW laser source that operated at a wavelength of 1030 nm, a repetition rate of 100 kHz and a pulse width tunable from 223 fs to 20 ps. When the pulse energy was changed from 36 μJ to 62 μJ and the pulse duration was changed from 12.5 ps to 20 ps, the nanopore structure with a diameter of 80~320 nm was successfully written on the ZnS crystal. The surface morphology, diameter and depth of the nanopores were determined by FIB (Focused Ion Beams) ablation and SEM (Scanning Electron Microscopy) imaging. The influence of laser pulse energy and pulse width on the nanopores was studied. The results show that when the pulse width is 20 ps and the pulse energy is 48 µJ, the depth of a nanopore is about 270 µm.
Abstract(45) FullText HTML(11) PDF 3379KB(4)
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Hybrid graphene/semiconductor phototransistors have attracted great attention because of their ultrahigh responsivity. However, the specific detectivity (D*) for such hybrid phototransistors obtained from source-drain electrodes is assumed to be 1/f noise. In this paper, D* of ~1.82×1011 Jones was achieved from source-gate electrodes. Compared with the same device which was measured from source-drain electrodes, D* was improved by ~500 times. This could be attributed to the carrier trapping and detrapping processes having been screened by the Schottky barrier at the interface. The rise and decay times were 4 ms and 37 ms, respectively. The temporal response speed also correspondingly improved by ~2 orders of magnitude. This work provides an alternative route toward light photodetectors with high specific detectivity and speed.
Abstract(131) FullText HTML(31) PDF 3956KB(24)
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Terahertz technology is indispensable in plenty of fields due to the abundant interactions between terahertz waves and matter. In order to meet the needs of terahertz applications, the development of highly sensitive and portable terahertz detectors based on distinctive physical mechanisms and various materials with excellent properties are urgently required. Black arsenic-phosphorus is a novel two-dimensional material that has a tunable band gap and transport characteristics with varying chemical composition, which has gained widespread interest in optoelectronic applications. Recent research on b-AsxP1-x mainly focuses on infrared detection, while the detection of terahertz has not yet been applied. Herein, an antenna-coupled terahertz detector based on exfoliated multilayer black arsenic-phosphorus is demonstrated. The terahertz response performance of the detector reflects two different mechanisms, which have a competitive relationship in the detection process. In particular, the detection mechanism can be tailored by varying the chemical composition of black arsenic-phosphorus. By balancing the band gap and carrier mobility, a responsivity of over 28.23 V/W and a noise equivalent power of less than 0.53 nW/Hz1/2 are obtained at 0.37 THz. This implies that black arsenic-phosphorus has great potential in terahertz technology.
Abstract(151) FullText HTML(94) PDF 5583KB(35)
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The discovery of the topological quantum states of matter is a major milestone in condensed matter physics and material science. Due to the existence of special surface states (e.g. Dirac fermions, Weyl fermions, Majorana fermions), topological quantum materials can usually exhibit some novel physical properties (such as the quantum anomalous Hall effect, 3D quantum Hall effect, Zero-band gap caused by topological states, ultra-high carrier mobility, etc.), which are different from conventional semiconductors. Because of this, there is an abundance of prospects for applications in low-power electronic and optoelectronic devices, especially in broad-spectrum detection. However, the application of topological quantum materials in the field of photoelectric detection is still in the exploratory stage at present. This article reviews the characteristics and preparation methods of topological quantum materials and the development status with respect to optical-sensing materials in photodetectors. The structure and performance of the devices based on topological quantum materials are also mentioned as the development prospects in the field of broad-spectrum detection.
Abstract(93) FullText HTML(174) PDF 4134KB(11)
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In recent years, a series of new low-dimensional optoelectronic materials with excellent properties have emerged. Combined with Surface-Enhanced Raman scattering (SERS) technology, they show great application potential and are expected to become highly sensitive SERS substrates. Defects and interface regulation of low-dimensional optoelectronic materials are important strategies for their applications in SERS technology. In this paper, the types and enhancement mechanisms of defects- and interface-enhanced Raman scattering in new low-dimensional optoelectronic materials are introduced. By looking forward to the application and research prospect of defects- and interface-enhanced Raman scattering, this work might inspire people to reconsider and further understand the study of SERS.
Abstract(135) FullText HTML(34) PDF 3506KB(3)
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One-dimensional (1D) semiconductor nanowires have shown outstanding performance in nano-electronics and nano-photonics. However, the electrical properties of the nanowire transistors are very sensitive to interactions between the nanowires and substrates. Optimizing the device structure can improve the electrical and photodetection performance of nanowire transistors. We report a suspended In2O3 nanowire transistor fabricated by one-step lithography, showing a high mobility of 54.6 cm2V−1s−1 and a low subthreshold swing of 241.5 mVdec−1. As an ultraviolet photodetector, the phototransistor shows an extremely low dark current (~10−13 A) and a high responsivity of 1.6×105 A•W−1. This simple and effective method of suspending the channel material of a transistor can be widely used in manufacturing high-performance micro-nano devices.
Abstract(116) FullText HTML(62) PDF 4084KB(9)
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In order to measure the micro-displacement of a fluorescent substance, we propose a nanofluidic channel-resonant cavity structure. Firstly, by using the Finite-Difference Time-Domain (FDTD) method, the influences of the quantum dot’s polarization state and structural parameters on the coupling effect of fluorescence and structure are studied and the structure is optimized. Then, the micro-displacement of the fluorescent substance is detected by measuring the change in the optical power output of the coupled structure. Finally, the factors affecting the sensitivity of the sensors are studied. The results show that, compared with the traditional method, when the refractive index of the nanofluidic channel-resonant cavity coupling structure is in the 2.8~3.3 range, the structure can sense of the micro-displacement of a fluorescent substance with high accuracy. The results also show that the sensing sensitivity can be further improved by reducing the distance between the nanofluidic channel and the resonant cavity.
Abstract(81) FullText HTML(28) PDF 6255KB(13)
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To achieve weak signal detection, high sensitivity is required. Because of their strengths in optical and electrical properties such as wide spectral absorption, adjustable bandgap, and high carrier mobility, graphene, Transition Metal chalcogenides (TMDs), Black Phosphorus (BP) and other two-dimensional (2D) materials have been used to fabricate infrared detectors. However, those 2D materials have disadvantages of weak light absorption, low carrier mobility and air instability, that restrict their applications in high-sensitivity infrared detection. Compared with single two-dimensional materials, heterostructures consisting of two or more single 2D materials adopt the characteristics of each single material as well as some novel physical properties from heterojunctions/interfaces. In recent years, the heterostructure of 2D materials has been studied extensively in the field of high-sensitivity infrared detection. To gain a deep understanding of the factors affecting sensitivity, we provide a comprehensive review of the strategies that improve the sensitivity of infrared detectors and the development of high-sensitivity infrared detectors based on 2D heterojunctions in recent years. We summarize the figures of merit of these infrared detectors and identify the existing challenges impeding further improvements in sensitivity. Finally, by summarizing the challenges of future improving the sensitivity of infrared detection prospects for strategies to obtain high-sensitivity infrared detectors with good comprehensive performance and commercial applicability are presented with considerations for balancing the detector’s responsivity and response speed, large area two-dimensional heterojunction preparation, heterojunction interface optimization, and so forth.
Abstract(253) FullText HTML(80) PDF 3577KB(57)
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At present, the power conversion efficiency of perovskite solar cells exceeds 25%. Their rapidly increasing efficiency has made people increasingly optimistic about their commercial application, but the stability of perovskite remains the biggest obstacle to successful commercialization. Quasi-two-dimensional perovskite solves this problem. Utilizing the hydrophobicity and thermal stability of large organic spacer cations, quasi-two-dimensional perovskite can effectively improve the stability of perovskite and improved crystal formation energy while providing a more stable structure. Quasi-two-dimensional perovskite also invites significant improvement to the morphology of perovskite films, which can replace anti-solvent processes, simplify production, and meet the industrial production requirements of perovskite. However, the relatively large band-gap and low carrier mobility caused by insulated organic spacer cations hinder ion transmission, causing quasi-two-dimensional perovskite solar cells to be far less efficient than three-dimensional perovskite solar cells. Therefore, for quasi-two-dimensional perovskite, it is necessary to further study its characteristics and device applications to achieve further optimization of device performance. This article summarizes the research progress of quasi-two-dimensional perovskite solar cells, the molecular structure of quasi-two-dimensional perovskite, the methods and principles of quasi-two-dimensional doping that improves the stability of three-dimensional perovskite, and the phase distribution and carrier transport characteristics of quasi-two-dimensional perovskite. Then this paper analyzes the problems faced by quasi-two-dimensional perovskite solar cells and looks forward to their prospects. It is expected that it will provide a reference for the preparation of efficient and stable quasi-two-dimensional perovskite solar cells.
Abstract(67) FullText HTML(25) PDF 6364KB(5)
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Gain ratio calibration error is one of the most significant factors affecting the accuracy of a polarization lidar depolarization ratio. This paper analyzes the basic principles of various existing gain ratio calibration methods and compares the advantages and disadvantages of the \begin{document}$+ 45^\circ$\end{document} method, \begin{document}$\pm 45^\circ$\end{document} method, \begin{document}$\Delta 45^\circ$\end{document} method, rotation fitting method and pseudo-depolarizer method in practice though experiments. Results show that: the \begin{document}$\Delta 45^\circ$\end{document} method, \begin{document}$\pm 45^\circ$\end{document} method and rotation fitting method are relatively accurate when the misalignment angle is small, but the operation of the \begin{document}$\pm 45^\circ$\end{document} method and rotation fitting method are more complicated. The \begin{document}$+ 45^\circ$\end{document} method still has a large calibration error without a misalignment angle. The pseudo-depolarizer method is the easiest to operate, but it is restricted by a non-ideal pseudo-depolarizer. Through comparison of theory and experiment, this paper provides a suggestion for the best choice of gain ratio calibration method. It is recommended that the \begin{document}$\Delta 45^\circ$\end{document} method be used for calibration with a half-wave plate, and the pseudo-depolarizer method be used for calibration with a high-precision depolarizer.
Abstract(36) FullText HTML(14) PDF 1984KB(5)
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To solve the data transmission difficulties and long-signal acquisition and processing time problem caused by excessive data transmission of the Geostationary Orbit array staring spectrometer, a scheme for a large-aperture visual and infrared snapshot spectrometer based on compressive sensing is proposed, which takes advantage of the fact that a geostationary orbit platform can stay over the fixed area for a long time. This paper analyzes the physical model of compressive sensing spectral imaging. The structure of the optical system is designed, and the relevant parameters are calculated. The objective lens uses a coaxial three-mirror afocal optical system, and dichroic films are used to split the spectrum. The relevant parameters were calculated according to requirements and the system was designed using optical software. After optimization, the optical system was shown to have a width of 400 km◊400 km, a visible area of 40 m GSD, an MWIR area of 400 m GSD, and an LWIR area of 625 m GSD. The results show that the MTF of the visible area is higher than 0.455 at 78.125 lp / mm. In mid-wave infrared, the MTF is higher than 0.518 at 33 lp / mm, and the MTF is higher than 0.498 at 20.8 lp / mm in long-wave infrared. The spectral resolution of the visible light is 20 nm, the mediumwave infrared region’s resolution is 50 nm, and the long-wave infrared spectrum resolution is 150 nm. The second-order spectrum of the visual area is less than 0.05 mm. The optical system has good imaging performance and the imaging quality of each part of the optical system is close to the diffraction limit, which meets the needs of applications and indicators.
Abstract(22) FullText HTML(7) PDF 4015KB(2)
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Bi3+ doped Lu1-xO3: x%Ho3+ metal ion phosphors were prepared using the high-temperature solid-phase method. The crystal structures of Bi3+ doped Lu1-xO3: x%Ho3+ phosphors, the Bi3+→Ho3+ energy transfer in Lu2O3 matrix and the luminescent properties of a synthetic powder were investigated. X-ray diffraction results showed that Bi3+ and Ho3+ doping had no effect on the cubic phase structure of Lu2O3. Lu2O3: Ho3+, Bi3+ phosphor emitted 5S25I8 transition of Ho3+ at 551 nm under an excitation wavelength of 322 nm, and exhibited 1S03P1 characteristic transition of Bi3+ at 322 nm and 5I85F1 transition of Ho3+ at 448 nm under an emission wavelength of 551 nm. When the doping concentration of Bi3+ was 1.5%, the effect was most effective for the energy transfer of Ho3+, which increased by a factor of 34.8 compared to that of the single-doped Ho3+ sample. For the synthesis of 1%, 1.5%, 2% Bi3+ doped Lu98.5%O3: 1.5% Ho3+ samples, the luminescence intensity at 551 nm under 980 nm increased by a factor of 13.3, 16.8 and 14.2, respectively, compared to that of under 322 nm of excitation. The energy transfer critical distance between Bi3+ and Ho3+ was calculated to be 2.979 nm, and the energy transfer between Bi3+ and Ho3+ was achieved by dipole-quadrupole interaction.
Abstract(70) FullText HTML(18) PDF 4545KB(5)
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Acoustic-to-seismic coupling landmine detection technology based on the unique mechanical characteristics of landmines and the acoustic-to-seismic coupling principle has broad application prospects in safe and effective detection of landmines. However, a significant amount of work must be done to study the practical landmine detection system. Among them, the acoustic coupled surface vibration signals are very weak and complicated, which has always been a challenging problem to detect such signals accurately and quickly. In this paper, the non-contact laser measurement techniques of surface vibrations based on the principle of the acoustic-to-seismic coupling landmine detection technology were reviewed, including laser Doppler interferometry, electronic speckle pattern interferometry and laser self-mixing interferometry, etc., and the application feasibility of electronic speckle-shearing pattern interferometry in acoustic-to-seismic coupling landmine detection was explored.
Abstract(65) FullText HTML(19) PDF 3846KB(3)
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During its propagation in atmospheric turbulence, the optical properties of a laser beam will be changed by the surrounding environment. Compared with a completely coherent laser, a partially coherent laser can more strongly resist the influence of atmospheric turbulence. In this study, a twisted Laguerre-Gaussian correlated beam was employed to deduce a cross-spectral density function for propagation in atmospheric turbulence. The cross-spectral density and M2factor were also constructed by using the extended Huygens-Fresnel diffraction integral principle, Wigner distribution function, basic properties of the twisted phase, and power spectrum model of non-Kolmogorov turbulence. Then, the influence of atmospheric turbulence on the beam was numerically simulated, and the results were compared with those for different twist factors, transverse coherence parameters and mode orders. It has been demonstrated that a beam with a high twist factor, low transverse parameter, and high mode order can be used to effectively suppress the influence of atmospheric turbulence. The conclusions of this paper might be useful in improving the transmission performance of a laser beam in atmospheric turbulence.
Abstract(43) FullText HTML(19) PDF 3569KB(0)
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A laser loading model for coating samples is established. The coupling process of the laser energy is simulated based on the parameters of the materials and the temperature rise characteristics are analyzed with different parameters. The reflective characteristics of SiCN coating on a copper substrate are then investigated. Through a series of laser radiation experiments, the laser-induced damage of the coating is examined by recording the temperature threshold for the coating. This paper provides research support for the material selection and parameter design of laser energy measurement devices.
Abstract(48) FullText HTML(26) PDF 3827KB(5)
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In the field of aspheric testing, computer-generated hologram (CGH) technology has been widely used. CGH encoding, which is the conventional encoding method to achieve highly accurate coding, uses an amount of data that is often up to tens or even hundreds of gigabytes. Therefore, in order to achieve high encoding accuracy with a small amount of encoded data, this paper proposes a variable step size CGH encoding method. This method selects different sampling frequencies by calculating the phase distribution gradient so that the CGH achieves high precision coding using as few points as possible. Finally, the method was used to CGH encode, then the resulting CGH was manufactured to test an aspheric surface. The test result had 3.142 nmRMS. In order to verify the credibility of the test results, this paper designs and makes a compensator to test the same aspheric surface. The test result had 3.645 nmRMS. The difference between the two results is 1.291 nmRMS, and shows that the encoding method can meet the requirements of high-precision testing of aspheric surfaces.
Abstract(75) FullText HTML(34) PDF 3314KB(5)
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In order to address the light modulation problem on repair spots created after using a CO2 laser to repair fused silica surface damage, this paper focuses on the change of the profile and the modulation of the repaired sites before and after coating them with antireflective film. The influence of the depth and width of the repaired site on the deposition of the colloid are discussed, with some attention also given to the influence of the modulation effect. The results indicate that the colloidal material significantly enriches the pits of a repair, which can effectively improve their topographic dimensions with regards to their depth. The maximum modulation locations of a repaired site will increase after being coated with the antireflective film. However, the maximum modulation caused by the repaired site is much smaller than that of the corresponding uncoated repair point. The results of this study can provide reference for further optimization of repair processes and light modulation regime control of the surface damage sites on fused silica.
Abstract(101) FullText HTML(24) PDF 9976KB(7)
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In space-based gravitational wave detection, laser interferometry is utilized to achieve ten-picometer precision in the displacement measurements between drag-free proof masses. Laser frequency noise and clock frequency noise are the two dominant noises in the measurement. In the European LISA (Laser Interferometer Space Antenna) program for gravitational wave detection, the Time-delay Interferometry technique, TDI, is used to cancel laser noise and optical bench noise by time-delaying and linearly combining the twelve phase measurement data of the three satellites and thus creating an interferometer with equal-length beams. For the cancellation of clock noise, the frequencies of onboard clocks are multiplied to GHz levels and then the inter-satellite laser links are phase modulated by GHz clock signals. Finally, the clock noise can be extracted from the generated clock-sideband beat note, eliminating the clock noise terms in the TDI data combination. For the time-delay operation in the data post-processing of the TDI, there is also a requirement for the precise measurement of the absolute distances between three satellites. Therefore, in the TDI scheme, there are three functions applicable to the inter-satellite laser links: displacement measurement, clock sideband modulation and absolute distance ranging. The latter two functions consume the power of the optical carrier by 10% and 1%, respectively. The TDI demonstration in the LISA’s ground-based testbed shows the laser noise and clock noise can be suppressed by the factor of 109 and 6×104, respectively. The TDI technique is of important value for China’s gravitational wave detection program and other space-based laser interferometry missions.
Abstract(57) FullText HTML(22) PDF 4603KB(3)
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Objective  To achieve multi-optical axis calibration of the Space Photoelectric Tracking and Aiming System in a vacuum.  Method  this paper first designed a set of multi-axis calibration systems based on the accuracy requirements for multi-axis consistency detection of the Space Photoelectric Tracking and Aiming System. Then, a detailed error analysis of each subsystem of the multi-axis calibration system was conducted, and the methods to limit error in the key subsystem were given. After that, the technical tests of the space photoelectric tracking and aiming system of the communications technology test satellite 3 were implemented in laboratory and vacuum environments, and the error sources and test accuracy of the multi-axis calibration system in the two test environments were analyzed to produce test results. Finally, the accuracy of the multi-axis calibration system was verified.  Result  The final results show that the calibration accuracy of the multi-axis calibration system designed in this paper is 0.998" in the laboratory test environment, and the calibration error of the parallelism of transmitter and receiver is 1.165"; the calibration accuracy is 1.219" in the vacuum test environment, and the calibration error of parallelism of transmitter and receiver is 1.359".  Conclusion  These results fully meet the 1.5" multi-optical axis detection accuracy requirements of the space photoelectric tracking system, and provides support for research in related engineering applications.
Abstract(62) FullText HTML(25) PDF 3775KB(8)
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The averaging of multiple B-Scans is an effective method of reducing speckle noise in swept-source optical coherence tomography (SS-OCT) and obtaining clear structural information. However, physiological characteristics such as eye tremor, drift, micro-saccade, and the optical structure of an SS-OCT system cause geometric transformation between images, resulting in poor multi-frame averaging. In this paper, we propose a registration algorithm based on the combination of gray distribution information and target geometric information. This method extracts the region of interest containing target information using the average gray distribution of an image, and corrects the transformation of the image with the collective effect of the phase correlation algorithm and the gray projection algorithm based on the fitting of the curve of its segments. Then, the process is repeated with the upper boundary of the retinal image fitted as the feature points to determine the optimal rotation parameters. The translation parameters are re-estimated again to achieve the rigid registration of the image. Finally, a one-to-one mapping method of axial scanning is used to achieve the non-rigid registration of the image with the energy function as the constraint. Experiments on live rabbit eyes show that the averaged image has clear boundaries, enhanced structural information, and its signal-to-noise and contrast-to-noise ratios are more than doubled their previous values, on average. The algorithm is suitable for the registration of B-Scan images with strong speckle noise and can meet the averaging needs of many types of OCT systems. It has high robustness and image registration accuracy.
Abstract(125) FullText HTML(44) PDF 4667KB(11)
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Problems with existing polarization defogging algorithms are that they are not robust and have limited image enhancement abilities. To resolve this, an image fusion defogging algorithm based on multi-scale singular value decomposition is proposed. Firstly, the redundancy in polarization measurement information is used, and the least square method is used to improve the accuracy of the polarization information in the traditional defogging algorithm for polarized images; then, with respect to the limitations of that algorithm, a qualitative analysis of the feasibility of image fusion defogging is provided, and a polarized image fusion defogging algorithm based on multi-scale singular value decomposition is proposed. Finally, for verification, an experiment under different visibility conditions is designed and quantified. The results show that compared with the classic polarized image defogging algorithm, this algorithm does not require manual parameter adjustment, has strong adaptability and robustness, and can effectively improve the overexposure of halos and sky areas that occur in the traditional algorithm. The image information entropy and the average gradient can be increased by 18.9% and 38.4% respectively, which effectively improves the quality of visual imaging under complex lighting conditions. The proposed algorithm has great application prospects.
Abstract(78) FullText HTML(20) PDF 2044KB(3)
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Investigating polarization changes in a turbulent atmosphere holds great significance because polarization is one of the most important parameters in laser communication. Based on the extended Huygens-Fresnel principle and the unified theory of coherence and polarization, an analytical expression for the degree of polarization (DoP) in partially coherent Airy-Gaussian beams propagating in a slanted turbulent atmosphere is derived. It is then used to study the dependence of polarization changes in turbulent parameter, coherence length, zenith angle, truncation and distribution factor. The polarization between the slanted and horizontal paths is also compared. Compared with horizontal turbulence, the beams traverse a longer distance to recover their initial polarization in slanted turbulence. An increase in the zenith angle, receiving height and truncation factor, or a decrease in the coherence length can increase the DoP. A smaller distribution factor or a higher coherence length is beneficial to reducing the effect of the zenith angle on the polarization. Analysis of the influence of the distribution factor on polarization also shows that maintaining the polarization of a Gaussian beam with higher coherence in a horizontally turbulent atmosphere has a greater advantage to that of a pure Airy beam from the view of keeping polarization invariance. The results in this paper may be useful for studying atmospheric communication, and show that optical information encoding can be achieved by selecting appropriate parameters.
Abstract(170) FullText HTML(36) PDF 3339KB(4)
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Lanthanide ion doped upconversion luminescence is limited by the small absorption cross-section and narrow absorption band of lanthanide ions, which results in weak luminescence. Recently, a dye-sensitized method has proven to be an effective strategy of increasing upconversion luminescence. However, simply attaching dye molecules to nanoparticles with classic Yb-doped nanostructures cannot effectively activate the sensitizing ability of the dye molecules. In response to this problem, we designed Nd-sensitized core/shell/shell (NaYF4: Yb/Er (20/2%)@ NaYF4: Yb (10 %)@ NaYF4: Nd (80 %)) nanostructures, which compared with the classic IR-806 sensitized NaYF4: Yb/Er nanostructure, their upconversion luminescence (500 to 700 nm) was approximately enhanced by a factor of 38. Through analysis of the nanostructure’s emission and luminescence lifetime data, the enhancement was confirmed by the effective overlap of Nd absorption with the emission of near-infrared dye molecules and the protective effects of the shell structure on the luminescent center (the lifetime of Er (4S3/24I15/2) was increased by 1.7 times). In addition, we found that the doping Yb3+ in the outermost layer will decrease the dye-sensitized luminescence intensity. Furthermore, this Nd-sensitized core/shell/shell also achieved enhancement in the sensitized upconversion luminescence of the luminescence centers of Ho and Tm, which establishes a foundation for enhanced dye-sensitized upconversion luminescence.
Abstract(117) FullText HTML(33) PDF 3931KB(15)
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As a new rapid element analysis technique, laser-induced breakdown spectroscopy (LIBS) has proven iteself to have great potential for applications in increasingly numerous industrial fields. However, due to harsh outdoor and industrial environments, newer and higher requirements are being demanded of the LIBS system, such as the size of its instruments and the ability to resist a harsh environment. The rapid development of new laser technology promotes instrumentation for LIBS, allowing it to gradually step outside the laboratory and into the industry, and allows the LIBS system to gradually move towards instrumentation, miniaturization and portability.In this paper, the development of a portable LIBS that was developed in recent years was reviewed. The application and latest research progress of different kinds of laser source (small lamp pumped solid-state laser, diode pump solid-state laser and micro laser, fiber laser) applied to the portable LIBS system were summarized and discussed, providing insight into both the fiber optic LIBS (FO-LIBS) and the handheld LIBS. In addition, the basic problems of current portable LIBS and the prospects of its future were proposed and discussed.
Abstract(150) FullText HTML(39) PDF 4215KB(19)
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High-performance night vision light detection is the future direction of development in photoelectric detection. In this paper, a real-time polarization imaging technology for low-light imaging is proposed to solve issues where polarization images show large error due to low sensitivity. By introducing white light channels and 8 polarization channels in four polarization directions, detection can be achieved on EMCCD micro-optical devices. The experiment shows that the polarization information obtained by the polarization array is highly accurate, and also has advantages for its low difficulty in processing and its low cost.
Abstract(95) FullText HTML(37) PDF 4724KB(3)
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Objective  The sugar content and moisture of red globe grapes are important internal quality measurement indices. However, traditional detection methods use destructive biochemical detection.  Method  In this paper, a non-destructive detection method for the sugar and moisture content of red globe grapes based on visible/near-infrared spectroscopy transmission technology is studied. 360 red globe grape extract samples were collected and PLSR models were established by Standard Normal Variable transformation (SNV), SavitZky-Golay(S_G) and other spectral preprocessing methods to determine the one. Seven data dimensionality reduction methods of primary dimensionality reduction (GA, SPA, CARS, UVE) and secondary dimensionality reduction combinations (CARS-SPA, UVE-SPA, GA-SPA) were used to identify characteristic variables of spectra. PLSR and LSSVM content detection models of red globe grape extract sugar content and moisture content were established respectively, and the advantages and disadvantages of each model were compared and analyzed.  Result  The results show that the optimal PLSR model wavelength extraction method for red globe grape sugar content and moisture content is GA-SPA-PLSR, and the correlation coefficients of the optimal model were 0.958 and 0.938, respectively. The optimal LSSVM model wavelength extraction methods for red globe grape sugar and moisture content are CARS-SPA-LSSVM and UVE-SPA-LSSVM, respectively. The correlation coefficients of the optimal model are 0.969 and 0.942, respectively. The model built using LSSVM is better than that built using PLSR, but its operation time is longer.  Conclusion  The results show that: The non-destructive detection method of red globe grape sugar and moisture content based on visible/near-infrared technology is feasible, and that the detection accuracy of the two optimal detection models is high, which can meet detection requirements. Different models can be selected for different applications. The optimal model built by PLSR has shorter computation time and is suitable for online rapid detection. LSSVM has the best detection performance and can accurately predict red globe grape sugar and moisture content.
Abstract(106) FullText HTML(36) PDF 3199KB(21)
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Optical free-form surfaces are difficult to detect due to their rich degrees of freedom. Interference detection methods are both highly precise and non-contact. However, the static compensator in a traditional interferometer faces difficulty in achieving in-situ tests of unknown surface shapes or those changing during fabrication. Therefore, programmable adaptive compensators for large dynamic ranges have become a well-researched topic in recent years. Combined with the research work in the field of freeform surface metrology, this paper introduces the latest research progress in adaptive interferometry for optical freeform surfaces. Adaptive interferometers based on a deformable mirror (DM) or liquid crystal spatial light modulator (LC-SLM) are analyzed in detail. An adaptive controlling algorithm in the adaptive interferometer is introduced as well. Finally, the advantages and development bottleneck of the above two kinds of adaptive interferometry are summarized and prospects the future development of freeform surface adaptive interferometers are proposed.
Abstract(60) FullText HTML(29) PDF 3874KB(0)
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The signal intensity of laser-induced breakdown spectroscopy can be improved by increasing sample temperature and confining space confinement. The combination of the two techniques can further improve the spectral intensity of laser-induced breakdown spectroscopy. In this paper, the effects of increasing a sample’s temperature and spatial confinement on laser-induced breakdown spectroscopy (LIBS) are studied in air, and the time-resolved spectra of laser-induced aluminum plasma are measured. The experimental results show that increasing the sample’s temperature can increase the signal intensity of LIBS since a sample with a higher temperature can absorb more laser energy; when the cylindrical cavity is used to confine the plasma, the spectral emission is further improved. The effect of the combination of the two experimental conditions is that the signal intensity of LIBS is significantly stronger than that of either condition alone. The intensity of Al (I) 396.2 nm increases to 1.4 times at 200°C with higher temperature conditions alone, 1.3 times when spatial confinement is applied alone, and 2.1 times at 200°C with spatial confinement. The emission intensity with the combined effects is higher than the sum of that under the two individual conditions. The effect of the combination is mainly based on the fact that laser irradiation of the sample under a higher temperature generates stronger shock waves that can more effectively compress a larger-sized plasma plume, thereby further improving the spectral intensity of LIBS.
Abstract(103) FullText HTML(49) PDF 3845KB(19)
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Quasi-distributed fiber sensing systems play an important role in the fields of civil engineering, energy surveying, aerospace, national defense, chemicals, etc. Interrogation technology for quasi-distributed fiber sensing systems based on microwave photonics is widely used in high-speed and high-precision signal demodulation and sensor positioning in optical fiber multiplexing systems. Compared to conventional optical wavelength interrogation, this technology greatly improves system demodulation rate and compensates for the defects of traditional sensor positioning methods. This paper introduces the recent research progress of quasi-distributed fiber sensing interrogation technology based on microwave photonics; compares and analyzes the advantages and disadvantages of several existing microwave demodulation systems from the perspective of their fiber grating quasi-distributed sensing and fiber Fabry-Perot quasi-distributed sensing systems, respectively; and provides a summary of the prospective direction of future research in quasi-distributed fiber sensing interrogation technology based on microwave photonics.
Abstract(146) FullText HTML(23) PDF 4273KB(9)
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Abstract(110) FullText HTML(64) PDF 3945KB(14)
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Resolution in a confocal microscope is limited by the size of its pinhole,. Structured modulation has been proven to be able to achieve super-resolution in confocal microscopy, however, its limited speed in image acquisition limits its applicability in real-world applications. In order to improve its imaging speed, we attempt to introduce a method that achieves rapid super-resolution confocal microscopy using line-scanning and structured detection. A cylindrical lens was used to focus the light into a line, and a digital mask with a sinusoidal function was used to modulate the raw image in the light detection arm. Unlike the virtual structured method, there is no need for a subsequent frequency shift process. In order to improve the isotropic resolution of the system, a scanning angle of 0 ° and 90 ° was achieved by rotating the sample. Simulation and experiment results indicate that coherent transfer function expands and the resolution is 1.4 times as large as that of a conventional confocal microscope. This method increases the system’s imaging speed 104-fold when compared with a confocal structured modulation microscope that uses spot-scanning.
Abstract(80) FullText HTML(42) PDF 3406KB(8)
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In order to improve the accuracy of the projector calibration in 3D shape measurement using digital fringe projection, a new projector calibration method that combines secondary projection technology and cross-ratio invariance is proposed. The secondary projection technology is used to compensate for the mutual interference between the projection pattern and the pattern on the calibration board, and the cross-ratio invariance method is used to avoid introducing camera calibration error. A comparative experiment is carried out to verify the effectiveness of the proposed method. Compared with the traditional method of projector calibration that requires camera parameters and that using global homography, the RMS values of reprojection error of this method is reduced from (0.2275, 0.2264) and (0.1237, 0.1098) pixels to (0.0535, 0.0468) pixels, and the maximum value of the reprojection error is reduced from 1.222 pixels and 0.5667 pixels to 0.2389 pixels. In addition, this method allows the camera to be simultaneously calibrated during operation, and therefore the parameters of the entire 3D measurement system can be acquired. The above results show that the method proposed in this paper can prevent errors in transmission of camera calibration parameters and improve the calibration accuracy of a projector.
Abstract(115) FullText HTML(56) PDF 3791KB(10)
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In order to improve the spectral calibration accuracy of the Large Aperture Static Imaging Spectrometer when its field of view is increased, and to reduce the influence of radial distortion on its spectral accuracy, this paper proposes a corrective method for spectral calibration coefficients based on a spectral distortion correlation model. To begin the process, the wave number and wavelength correction formulas are given. Using 594.1 nm and 632.8 nm gas lasers, a spectroscopic imaging experiment was performed on the imaging spectrometer, and the data was processed and analyzed. The results show that when there is a barrel distortion of 0.3%, the inversion spectrum at the edge of the field of view shifts approximately 2 nm. After implementing the corrective method of this paper, the line shift is reduced to approximately 0.1 nm. This method only needs to be corrected according to the lens distortion parameters, which simplifies the laboratory spectral calibration process and improves work efficiency. It can also be applied to the orbit parameter correction of spaceborne interference spectral data.
Abstract(122) FullText HTML(39) PDF 3572KB(14)
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With its unique advantages, visible light communication (VLC) can compensate for limitations in radio frequency communication, allowing it to become a recent avid topic of research. Orthogonal Frequency Division Multiplexing (OFDM) has been widely used in VLC due to its high rate of data transfer and frequency selective fading resistance. We present a comparative performance evaluation of several OFDM modulation techniques in VLC, including unipolar schemes, enhanced schemes and hybrid schemes based on discrete Fourier transformation, as well as optical OFDM systems based on Hartley transform and LED index modulation. We perform these comparisons in terms of energy efficiency, spectral efficiency, bit error rate, and algorithm complexity. The principles of some kinds of optical OFDM systems are firstly illustrated and their spectrum efficiencies are theoretically analyzed and compared. We also provide research and analysis of the improved design of receivers in optical OFDM systems. The challenges and upcoming research of OFDM systems in VLC are summarized. We induce optical OFDM systems in this paper, providing a research reference and proposing more efficient unipolar modulation schemes to further improve the spectral efficiency and reliability of optical OFDM systems.
Abstract(150) FullText HTML(54) PDF 3432KB(18)
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Polarization modulation technology using electro-optic crystals is playing an increasingly important role in the field of three-dimensional laser imaging. Due to the low field of view and high half-wave voltage of LN materials, it is difficult for traditional electro-optic modulation technology to further improve 3D imaging performance. With perovskite-structured electro-optical materials becoming more and more mature, electro-optic modulation technology using new materials will become an excellent means to create a breakthrough in the detection accuracy of laser 3D imaging. PMNT, PLZT and KTN three typical materials have excellent electro-optical properties and dielectric properties that might surpass the field of view and half-wave voltage limitation. However, their applications in electro-optic modulation has lead to difficulties such as a low PMNT modulation bandwidth, poor PLZT transmission performance, and low KTN practical application bandwidth. Future research will focus on the practicality of this modulation technology. The technology’s electro-optic modulation performance can be improved with doping and the signal-to-noise ratio of the system can be optimized by establishing performance characterization models.
Abstract(141) FullText HTML(58) PDF 1988KB(6)
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Objective  In order to achieve the quantitative evaluation of the stray light attenuation in optical systems, we demonstrate a point source transmission test facility with 10−9-order sensitivity in this paper.  Method  We employed a pulsed source and measured the pulse to obtain the weak signal at the image plane, as well as to simplify the detection system. Using this scheme, we constructed a test facility with a maximum aperture of 600 mm and a test wavelength of 527 nm, and conducted the test with a 250 mm aperture optical system.  Result  Experimental results showed that the point transmission at a 60-degree incident angle is 1.68×10−9.  Conclusion  The results prove that the test error of this facility is in the order of 10−9 or below, and the test facility has the ability to test 10−9-order point source transmissions. This technology can provide quantitative evaluation for various optical systems with strict stray light requirements, like astronomical telescopes, star sensors and spaced target monitor payloads.
Column
2020, 13(6): 1171-1181.   doi: 10.37188/CO.2020-0033
[Abstract](498) [FullText HTML](161) [PDF 7413KB](91)
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With its high speed, small size, light-weight and low power consumption, space laser communication has become an indispensable and effective means of high-speed communication between satellites, especially in micro-satellite applications, which can benefit more strongly from the advantages of laser communication. This paper provides a detailed introduction of the latest research progress in the field of micro-satellite laser communication technology. On this basis, key techniques such as light miniaturization of identical orbital terminals, light miniaturization of different orbital terminals and turbulence mitigation technologies are summarized, and the development trends of the technology’s applications, duplex communication, single-point to multi-point, localization and batch production capacity are concluded.
2020, 13(6): 1182-1193.   doi: 10.37188/CO.2020-0049
[Abstract](344) [FullText HTML](89) [PDF 3630KB](90)
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Target detection technology based on laser speckles is a kind of laser detection technology that has been ignored for a long time. In this technology, the laser speckle, which is regarded as noise in the traditional laser detection technology, is used as a new source of information. By analyzing the formation mechanism of a laser speckle pattern, the relationship between the statistical characteristics and the physical characteristics of the target is explored, and the effective analysis and inversion methods are combined to obtain the target’s shape, size, surface roughness and dynamic parameters. Compared with traditional laser detection technology, target detection technology based on laser speckles has a simple structure, has low optical system requirements, is sensitive to the physical and fretting characteristics of the target’s surface, and has been widely used in aerospace, medicine, industry, military and other fields. This paper classifies and summarizes the various kinds of speckle-based target detection technologies from recent years, compares and analyzes their applications, advantages and disadvantages, as well as the environmental restrictions. Finally, this paper prospects the trend for the future development of target detection methods based on laser speckles.
2020, 13(6): 1194-1208.   doi: 10.37188/CO.2020-0032
[Abstract](185) [FullText HTML](65) [PDF 3727KB](36)
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Segmented mirror technology is one of the three ways to realize optical synthetic aperture telescope, and it is an important area of development for future large aperture telescopes. A telescope’s active control system of its segmented mirrors directly determines its large aperture mirror’s optical performance. This paper focuses on the active control technology of large aperture ground telescopes with segmented mirrors. In this paper, we introduce the development process of a segmented mirror telescope and the main structure of the segmented mirror active control system, then summarize and analyze the domestic and foreign development of active control systems of segmented mirrors. In this paper, the key technologies of segmented mirror active control systems and how they achieve active adjustment and active maintenance are summarized. Their applications and the direction of their development are also proposed with respect to deep learning theory in closed-loop control, co-phase detection and correction, system-level simulation modeling technology. This paper provides guidance for the design of a segmented mirror control system in the next generation of ground-based large aperture telescopes in China.
2020, 13(6): 1209-1223.   doi: 10.37188/CO.2020-0131
[Abstract](150) [FullText HTML](79) [PDF 4987KB](42)
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The development of ultrafast laser technology has continuously injected new impetus into fundamental research and production, promoted the emergence of new disciplines and technologies. As a new materials welding and joining technique developed in recent years, ultrafast laser welding has attracted extensive attention due to the potential application in the fields of aerospace, precision machinery, optoelectronics, biomedical, etc.. Based on the intrinsic characteristic of non-linear space-selective energy deposition, ultrafast laser welding possesses extremely high material applicability and spatial selectivity, and can realize high-quality space-selective welding involving transparent materials with no need inserting an absorption layer. In this paper, we firstly give an overview on the progress of this field. Then, the physical mechanism, key influencing factors, and application scope of ultrafast laser welding are elaborated. At last, the future development and key challenges of ultrafast laser welding are discussed.
2020, 13(6): 1224-1238.   doi: 10.37188/CO.2020-0237
[Abstract](237) [FullText HTML](49) [PDF 6952KB](58)
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Ultra-precision displacement measurement technology is not only the basis of precision machining, but also plays a decisive role in the chip manufacturing industry that is rapidly developing in Moore's Law. The grating displacement measurement system based on the grating pitch is widely used in multidimensional measurement system. Compared with the laser displacement measurement system, grating displacement measurement system greatly reduces the environmental requirements for humidity, temperature and pressure. In this paper, the development status of the optical structure of displacement sensing system based on two-dimensional grating in recent years is introduced. The principles of zero-difference and heterodyne grating interferometrys are introduced. The optical structure based on single-block two-dimensional grating is reviewed. The development history of the optical structure in single-block two-dimensional grating to coupling designs of multi-block two-dimensional gratings is summarized, the advantages and disadvantages of several two-dimensional grating displacement measurement systems are compared and analyzed, and the development trend of two-dimensional grating displacement measurement system is prospected. The engineering process of two-dimensional grating displacement measurement system is summarized.
2020, 13(6): 1239-1248.   doi: 10.37188/CO.2020-0112
[Abstract](62) [FullText HTML](16) [PDF 3783KB](19)
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Composition analysis of the surface and depth distribution of bronze artifacts excavated from the Chu Tomb in Guozhuang Shangcai, Henan Province and ceramic tiles of Lingzhaoxuan from the Palace Museum are carried out by laser-induced breakdown spectroscopy and laser scanning confocal microscopy. Studies have shown that the elemental distribution of the corroded layer on the surface of bronze is uneven. This corrosion might originate from the surrounding soil environment and surrounding artifacts or ion migration from the artifacts’ insides to their outsides. Luckily, the composition of bronze is relatively simple. The corrosion mechanism of the corroded layer can be understood by analyzing the depth distribution of the composition in bronze, thereby providing a scientific method for its protection. The elemental distribution of ceramic is homogeneous in transparent and colored glaze. Colored glaze includes Boron (B), which could effectively reduce its melting temperature range and surface tension, but there is no boron (B) in transparent glaze. Furthermore, confocal microscope tests of the depth of erosion combined with its spectra can be used to estimate the approximate thickness of different glaze layers.
2020, 13(6): 1249-1256.   doi: 10.37188/CO.2020-0249
[Abstract](143) [FullText HTML](62) [PDF 2239KB](26)
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In this paper, a narrow linewidth laser with an external grating cavity of 638 nm is described, wherein a reflection holographic grating was used as its external feedback element. The spectrum of the diode lasers with the grating external cavity arranged in a Littrow configuration were measured using a high-resolution monochromator and the characteristics of the threshold and tuning properties were investigated. In the experiment, reflection holographic gratings with 2400 l/mm and 1800 l/mm groove density were studied. At 120 mA injection current, the output power of the external cavity laser was 45.2 mW when the groove density was 2400 l/mm, and the threshold current of the LD was reduced from 60 mA to 51 mA and the descent rate was 11%. When the groove density was 1800 l/mm, the output power was 38.7 mW, the threshold current of the LD was reduced from 60 mA to 47 mA, and the descent rate was 24%. Furthermore, the linewidths were suppressed to within 3.5 pm, and the tuning ranges were 9.4 nm and 10.5 nm in wavelength. The experimental results showed that the performance of semiconductor lasers was improved greatly using the Littrow configuration with a reflective holographic grating.
2020, 13(6): 1257-1266.   doi: 10.37188/CO.2020-0075
[Abstract](141) [FullText HTML](75) [PDF 3625KB](10)
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In order to achieve the implantation of the ZnO nanorod arrays in the nanostructured solar cells, it is necessary to tailor and control the nanorods’ morphology, optical and electrical properties. ZnO nanorods arrays were fabricated by electrodeposition. The physical properties such as the crystalline quality, diameter, density, distance, Al doping concentration, optical band gap energy, near band emission and stokes shift can be adjusted by using Al(NO3)3 and NH4NO3. The ZnO nanorods’ diameter can be adjusted from 28 nm to 102 nm. The nanorod arrays’ density can be reduced to 2.7×109 /cm2 by using NH4NO3, resulting in an increase in the distance between nanorods to 164 nm. The Al/Zn weight ratio was increased to 2.92% by using NH4NO3, indicating that NH4NO3 can boost Al doping in ZnO nanorods. The ZnO nanorods’ optical band gap energy can be tailored from 3.36 eV to 3.55 eV by using Al(NO3)3 and NH4NO3 and the near band edge emission can also be adjusted. The use of Al(NO3)3 led to the increase of the Stokes shift to 200 meV, but it can be greatly reduced to 26 meV as a result of the NH4NO3. The use of Al(NO3)3 and NH4NO3 resulted in the fabrication of high-quality ZnO nanorod arrays with effectively tailored morphology and optical properties.
2020, 13(6): 1267-1275.   doi: 10.37188/CO.2020-0053
[Abstract](176) [FullText HTML](72) [PDF 3425KB](9)
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To obtain the energy coupling characteristic of materials under strong explosive thermal radiation, a physical model for calculating radiation source parameters and atmospheric transmission is constructed, and the characteristics of the radiation spectrum at the target location under different conditions are obtained. The energy coupling coefficients of several kinds of materials are produced by spectral reflectance measurement and by calculating the average absorption coefficient of thermal radiation. The coupling coefficients of metal and ceramic materials are relatively small while it can be as high as 0.92 for carbon fiber epoxy composites. The coupling coefficient calculated from the actual thermal radiation spectrum is higher than that calculated from 6000 K blackbody radiation spectrum, and the maximum difference is about 14%. Taking aluminum material as an example, the coupling coefficient of thermal radiation decreases gradually with the increase of explosion yield and distance, but the overall variation is small.
2020, 13(6): 1276-1284.   doi: 10.37188/CO.2020-0089
[Abstract](169) [FullText HTML](68) [PDF 3486KB](20)
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According to the imaging principles and characteristics of a shutter CMOS image sensor, the shutter effect introduced by a shutter CMOS image detector operating on a star map is analyzed, and an image shift compensation method is proposed to rectify the image distortion introduced by this kind of imaging method. With the known frame frequency of the star images and the exposure time interval of the adjacent rows of the CMOS graphic sensor, this method can achieve high-speed calculation of star motion by extracting and matching the centroid of the star points in an adjacent star map. The centroid of the star points in a global image is calculated by combining the speed value with the row exposure time interval of the CMOS image sensor. The effect of the algorithm is tested on actual star images. The experimental results show that with the compensated star map, angle errors between the star sensors are smaller than 0.5″ when a satellite is in non-maneuver mode, and angle errors between either of the star sensors are about 0.6″ when the satellite is in maneuver mode. The experimental results not only prove the effectiveness of the algorithm, but also broaden the applications of shutter CMOS detectors to some extent, especially in aerospace engineering.
2020, 13(6): 1285-1292.   doi: 10.37188/CO.2020-0054
[Abstract](287) [FullText HTML](113) [PDF 4292KB](26)
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In view of the complex design of light sources and the poor illumination uniformity in cylinder block transverse hole detection by using machine vision, a double light source method is provided for the detection of transverse holes. In this method, an integrating sphere is used as the background light source and an LED is used as the direct light source. To achieve uniformity of illumination on the cylinder transverse hole, a mathematical model of the light source radiation response is established in this paper. Using this imaging method, a relationship between the size of the light source, its distance and the position of the reflection point and illumination uniformity is proposed. Finally, a controlled experiment was performed to reveal the illumination uniformity developed in different light sources: an optical fiber source, an LED source, and an LED + integrating sphere source. The results of the experiment show that the non-uniformity is up to 10% with an LED light source emitting from outside the hole, and it becomes 5% when the LED light is moved to the inside of the hole; the non-uniformity of an internal optical fiber light source is 4.6%. In particular, the double light source, wherein the integrating sphere is used as a background light outside the cylinder block and the LED is used as a direct light inside the cylinder block has a non-uniformity of 0.6%. The uniformity illumination surpasses 99%, which can be obtained by using an integrating sphere and LED dual light source, meeting our requirements for machine vision detection.
2020, 13(6): 1293-1301.   doi: 10.37188/CO.2020-0041
[Abstract](201) [FullText HTML](83) [PDF 3856KB](28)
Abstract:
In pavement detection, the small sample of road crack image data makes it difficult for neural networks to extract useful features from images. To solve this problem, this paper proposes a Gabor Filter Convolutional Neural Network (GF-CNN) model. The GF-CNN model first inputs a road surface image into a small parameter prediction network, adaptively selects the parameters of the Gabor filter bank according to the input, and constructs a filter bank according to the predicted parameters, and then filters the initial road surface image to obtain the Gabor texture feature map. The texture feature map is inputted into a feature classification network constructed by the residual network to extract deep features, at the same time, to judge whether a crack exists. Test results on the GAPs pavement image dataset show that the F1 score of the GF-CNN model reaches 0.7137, which is superior to other pavement image detection methods. This model improves the feature extraction ability of CNNs by fusing texture features, and reduces the sensitivity of Gabor filter parameters to improve its ability to make generalizations. It has good applicability to pavement crack image detection.
2020, 13(6): 1302-1313.   doi: 10.37188/CO.2020-0057
[Abstract](162) [FullText HTML](65) [PDF 4929KB](11)
Abstract:
To improve the detection accuracy and reduce the complexity of optical remote sensing of target images with a complex background, a global context detection model based on optical remote sensing of targets is proposed. First, a feature encoder-feature decoder network is used for feature extraction. Then, to improve the positioning ability of multi-scale targets, a method that combines global-contextual features and target center local features is used to generate high-resolution heat maps. The global features are used to achieve the pre-classification of targets. Finally, a positioning loss function at different scales is proposed to enhance the regression ability of the model. Experimental results show that the mean average precision of the proposed model reaches 97.6% AP50 and 83.4% AP75 on the NWPU VHR-10 public remote sensing data set, and the speed reaches 16 PFS. This design can achieve an effective balance between accuracy and speed. It facilitates subsequent porting and application of the algorithm on the mobile device side, which meets design requirements.
2020, 13(6): 1314-1323.   doi: 10.37188/CO.2020-0021
[Abstract](211) [FullText HTML](82) [PDF 3692KB](15)
Abstract:
In this paper, an identification method based on an improved differential evolution algorithm is proposed for laser communication fine tracking systems. Firstly, the basic principle and calculation steps of the traditional differential evolution algorithm are introduced. Based on this, an improved algorithm is proposed, and the algorithm’s parameters are optimized . Then, the dynamic characteristics of a controlled object in the fine tracking system are simulated by a sweep signal, and the positional feed back information of the camera is collected. Finally, based on the experimental data, the differential evolution algorithm is used to identify the system, and the control model of the fine tracking system is obtained. The experimental results show that the improved differential evolution algorithm has faster convergence speed and accurate identification results. In general, this method has engineering value in the field of optoelectronic tracking.
2020, 13(6): 1324-1331.   doi: 10.37188/CO.2020-0058
[Abstract](191) [FullText HTML](94) [PDF 3312KB](28)
Abstract:
Offner imaging spectrometers consist of a convex grating and two concave mirrors. The concentric characteristics of the optical structure allow it to have a large relative aperture, small distortion and a compact structure. In order to reduce the difficulty of aligning an Offner imaging spectrometer and improve its efficiency, this paper presents a fast alignment method for Offner imaging spectrometers based on the concentric characteristic and spherical autostigmatic method. Firstly, a spherical autostigmatic device is built, which can generate a point source. When the point source is located at the spherical mirror’s center of curvature (CoC), its reflection image point and the point source coincide. By measuring the distance between the reflection image point and the point source, the positional deviation of the spherical mirror’s CoC can be determined. The Offner imaging spectrometer is completed by locating the CoC of its primary mirror, convex grating and tertiary mirror. The results show that the location error of the two off-axis concave mirrors’ CoC can be controlled within 10 μm, and our imaging performance requirements for the imaging spectral system are satisfied. Compared with pre-existing methods, this method is easier to operate, lower in cost and has faster alignment capabilities.
2020, 13(6): 1332-1342.   doi: 10.37188/CO.2020-0043
[Abstract](180) [FullText HTML](69) [PDF 5073KB](32)
Abstract:
At present, it is difficult to obtain target distance information in image guidance. In order to apply modern guidance laws to image guidance technology and improve its performance, a target ranging algorithm using light field imaging is proposed. The algorithm decodes and tunes light field data to extract sub-aperture images from an original image. Bilinear interpolation is then performed on the two sub-aperture images to improve the image’s spatial resolution, and two sub-aperture images are selected as calibration data to obtain the corresponding internal and external parameters. The parameters are used to correct the sub-aperture images, which aligns them and makes them coplanar. Finally, a semi-global matching method is used to match the images to obtain the disparity value of the target. Then, 3D transformation of parallax can be used to get the target distance. The experimental results show that the average measurement errors of the algorithm are 28.54 mm and 14.96 mm, respectively, before and after improvement. This algorithm can effectively extract target distance information in complex scenes, which has value in theoretical and real-world applications.
2020, 13(6): 1343-1351.   doi: 10.37188/CO.2020-0024
[Abstract](140) [FullText HTML](57) [PDF 3778KB](25)
Abstract:
In order to achieve high-precision ground calibration of star sensors and meet the needs of a high-precision multi-star simulator with a wide field of view, a high-precision star simulator which can accurately simulate the position and magnitude of 65 stars in the 20° × 40° field of view was developed. Based on the principles of star simulators and the transformation of the space coordinate systems of star simulators, a simulation star bracket was designed. By the analysis and calculation of errors that affect the pointing error of star simulations, the high-precision simulation star system was designed using key technologies such as "integrated installation of primary and secondary mirrors", "all-aluminum simulation star systems" and "star point position compensation". A space-position model of each simulation star in the o-x'y'z' coordinate system was established, and the mathematical models of pitch, yaw, single star direction and star angular distance were derived. Also, the theoretical errors in single-star direction and star angular distance, which were used as the theoretical basis for adjustment and testing, were calculated. The single-star direction error of all simulated stars was better than 1.914", and the angular distance error of any two simulated stars was better than 4.3". The accuracy of the designed high-precision wide-field-of-view multi-star simulator meets the requirements. It can be used as an important piece of equipment for ground calibration of high-precision star sensors.
2020, 13(6): 1352-1361.   doi: 10.37188/CO.2019-0201
[Abstract](122) [FullText HTML](36) [PDF 5075KB](27)
Abstract:
To meet the performance requirements of ultra-lightweight Φ500 mm-reflector optical system in near diffraction limit, the structure of the reflector is studied using advanced CAE simulation and modern high-performance SiC fabrication technology. Firstly, mirror materials were selected by comparing the common materials and manufacturing processes of existing mirrors. Then, with regards to the structural characteristics of circular symmetrical reflectors, the structure of proposed reflector was designed based on integrated optimization of the full stiffness method. Finally, the reflector assembly was designed with a back-support structure. The simulation results show that the mass of proposed primary mirror is less than 5 kg and the surface density is less than 20 kg/m2. The surface errors (RMS value) of the three directions of dead weight deformation at 4 ℃ temperature rise are less than λ/50. The first-order resonance frequency of the primary mirror assembly is no less than 120 Hz and the stress at the weakest point as measured by dynamic response analysis is less than 100 MPa. The structural optimization of the mirror meets its design requirements, with a remarkable lightweight effect and a structure that is both stable and reliable.
2020, 13(6): 1362-1384.   doi: 10.37188/CO.2020-0056
[Abstract](228) [FullText HTML](83) [PDF 4683KB](26)
Abstract:
To enhance the blue light absorption of silicon, an array of silver nanoparticles(Ag-NPs) was designed so that they create Localized Surface Plasmon Resonance(LSPR) near the surface of silicon(Si). The properties of the enhanced optical absorption of silicon in the blue band were then observed and researched. The blue-light absorption characteristic of silicon in the Ag-NPs/Silicon composite structure were calculated using the Finite-Difference-Time-Domain (FDTD) method. The results indicated that the metallic nanoparticles' extinction capability was related to its geometric parameters and the resonance intensity and peak wavelength can be tuned according to different geometric parameters of Ag-NPs including radius, height and period. At a resonance peak wavelength of 465 nm, the optical absorption of Si in the composite structure (Ag-NPs/Si) rises from 59% to 94% with an array of radius r = 18.5 nm, a height H = 45.0 nm and a period P = 49.0 nm. It concluded that the light absorption gain was 0.57 and photogenerated carriers had a gain factor of 0.53 due to the enhanced light absorption of Si via LSPR in blue band. The results provide a significant reference for the enhancement of the blue-light absorption properties in silicon based on the LSPR effect and the design of a silicon-photodetector with a visible wide spectral resoponse.
2020, 13(6): 1385-1400.   doi: 10.37188/CO.2020-0071
[Abstract](161) [FullText HTML](82) [PDF 3198KB](18)
Abstract:
In order to obtain the first ionization threshold of Sm atom, the photoionization signal, autoionization signal and field ionization signal generated by the Sm atom under multi-step excitation were distinguished, and the influence of the Rydberg state of the Sm atom with different magnetic quantum numbers on the first ionization threshold was studied. At first, by use of multi-step resonance excitation combined with polarization technology, the rare-earth Sm atoms were excited to the autoionization or bound Rydberg state with a specific magnetic quantum number near the first ionization threshold. Then the ions generated by photoionization and autoionization were pushed out of the action zone by the reverse electrostatic field, and a delayed pulsed electric field was applied to detect the Sm atoms of bound Rydberg state. Finally, the relationship between the first ionization threshold of Sm atom and the varying intensity of electrostatic field was acquired, and the first ionization threshold of the Sm atom with different magnetic quantum numbers under zero field was determined by fitting. The experimental results show that the first ionization threshold of Sm atom is 45519.69±0.17 cm−1, which has been compared with the results obtained by other methods. The effectiveness of the delayed field ionization technique in measuring the first ionization threshold of Sm atom has been verified.
2020, 13(6): 1401-1410.   doi: 10.37188/CO.2020-0059
[Abstract](124) [FullText HTML](32) [PDF 3523KB](25)
Abstract:
Laser-Induced Fluorescence(LIF) has become a powerful technology for quantitative analysis of Polycyclic Aromatic Hydrocarbons(PAHs) in soils due to its fast detection speed and low operational cost, without sample preparation. However, there are many types of PAHs in soils, and their similar structures lead to overlapped issues in their laser-induced fluorescence spectra. It is challenging to quantify a single PAH in complicated soil without the chemical separation. In this paper, fluorescence spectra of PAHs in agricultural soil are obtained by a 266 nm mobile LIF system, and quantification methods are investigated for PAHs, based on univariate linear regression, weighted non-negative least squares Multivariate Linear Regression(MRL) and Support Vector Regression(SVR). The results show that the correlation coefficients of anthracene and phenanthrene are both less than 0.90, and the average relative errors are both more than 20% by using univariate linear regression. Compared with univariate linear regression, MLR improves the prediction accuracy of anthracene and phenanthrene in the soil contaminated with bi-component PAHs. However, the average relative errors are still over 20% in the soil contaminated with multicomponent PAHs. Finally, a SVR model optimized by grey wolf optimization combined with differential evolution(GWO-DE) is applied for concentration measurement of anthracene and phenanthrene in agricultural soil contaminated with multicomponent PAHs. The average relative error of anthracene decreases from 23.1% (MLR) to 5.02%, while in the case of phenanthrene decreases from 20.8% (MLR) to 4.83%. This study provides an efficient method to improve the accuracy of LIF in quantifying multicomponent PAHs in soils.
2020, 13(6): 1171-1181.   doi: 10.37188/CO.2020-0033
Abstract(498) FullText HTML(161) PDF 7413KB(91)
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With its high speed, small size, light-weight and low power consumption, space laser communication has become an indispensable and effective means of high-speed communication between satellites, especially in micro-satellite applications, which can benefit more strongly from the advantages of laser communication. This paper provides a detailed introduction of the latest research progress in the field of micro-satellite laser communication technology. On this basis, key techniques such as light miniaturization of identical orbital terminals, light miniaturization of different orbital terminals and turbulence mitigation technologies are summarized, and the development trends of the technology’s applications, duplex communication, single-point to multi-point, localization and batch production capacity are concluded.
2020, 13(6): 1182-1193.   doi: 10.37188/CO.2020-0049
Abstract(344) FullText HTML(89) PDF 3630KB(90)
Abstract:
Target detection technology based on laser speckles is a kind of laser detection technology that has been ignored for a long time. In this technology, the laser speckle, which is regarded as noise in the traditional laser detection technology, is used as a new source of information. By analyzing the formation mechanism of a laser speckle pattern, the relationship between the statistical characteristics and the physical characteristics of the target is explored, and the effective analysis and inversion methods are combined to obtain the target’s shape, size, surface roughness and dynamic parameters. Compared with traditional laser detection technology, target detection technology based on laser speckles has a simple structure, has low optical system requirements, is sensitive to the physical and fretting characteristics of the target’s surface, and has been widely used in aerospace, medicine, industry, military and other fields. This paper classifies and summarizes the various kinds of speckle-based target detection technologies from recent years, compares and analyzes their applications, advantages and disadvantages, as well as the environmental restrictions. Finally, this paper prospects the trend for the future development of target detection methods based on laser speckles.
2020, 13(6): 1194-1208.   doi: 10.37188/CO.2020-0032
Abstract(185) FullText HTML(65) PDF 3727KB(36)
Abstract:
Segmented mirror technology is one of the three ways to realize optical synthetic aperture telescope, and it is an important area of development for future large aperture telescopes. A telescope’s active control system of its segmented mirrors directly determines its large aperture mirror’s optical performance. This paper focuses on the active control technology of large aperture ground telescopes with segmented mirrors. In this paper, we introduce the development process of a segmented mirror telescope and the main structure of the segmented mirror active control system, then summarize and analyze the domestic and foreign development of active control systems of segmented mirrors. In this paper, the key technologies of segmented mirror active control systems and how they achieve active adjustment and active maintenance are summarized. Their applications and the direction of their development are also proposed with respect to deep learning theory in closed-loop control, co-phase detection and correction, system-level simulation modeling technology. This paper provides guidance for the design of a segmented mirror control system in the next generation of ground-based large aperture telescopes in China.
2020, 13(6): 1209-1223.   doi: 10.37188/CO.2020-0131
Abstract(150) FullText HTML(79) PDF 4987KB(42)
Abstract:
The development of ultrafast laser technology has continuously injected new impetus into fundamental research and production, promoted the emergence of new disciplines and technologies. As a new materials welding and joining technique developed in recent years, ultrafast laser welding has attracted extensive attention due to the potential application in the fields of aerospace, precision machinery, optoelectronics, biomedical, etc.. Based on the intrinsic characteristic of non-linear space-selective energy deposition, ultrafast laser welding possesses extremely high material applicability and spatial selectivity, and can realize high-quality space-selective welding involving transparent materials with no need inserting an absorption layer. In this paper, we firstly give an overview on the progress of this field. Then, the physical mechanism, key influencing factors, and application scope of ultrafast laser welding are elaborated. At last, the future development and key challenges of ultrafast laser welding are discussed.
2020, 13(6): 1224-1238.   doi: 10.37188/CO.2020-0237
Abstract(237) FullText HTML(49) PDF 6952KB(58)
Abstract:
Ultra-precision displacement measurement technology is not only the basis of precision machining, but also plays a decisive role in the chip manufacturing industry that is rapidly developing in Moore's Law. The grating displacement measurement system based on the grating pitch is widely used in multidimensional measurement system. Compared with the laser displacement measurement system, grating displacement measurement system greatly reduces the environmental requirements for humidity, temperature and pressure. In this paper, the development status of the optical structure of displacement sensing system based on two-dimensional grating in recent years is introduced. The principles of zero-difference and heterodyne grating interferometrys are introduced. The optical structure based on single-block two-dimensional grating is reviewed. The development history of the optical structure in single-block two-dimensional grating to coupling designs of multi-block two-dimensional gratings is summarized, the advantages and disadvantages of several two-dimensional grating displacement measurement systems are compared and analyzed, and the development trend of two-dimensional grating displacement measurement system is prospected. The engineering process of two-dimensional grating displacement measurement system is summarized.
2020, 13(5): 899-918.   doi: 10.37188/CO.2020-0035
Abstract(470) FullText HTML(155) PDF 2407KB(84)
Abstract:
In recent years, carbon nanodot (CDs) have been widely researched due to their unique luminescent properties, good biocompatibility, low toxicity and high photostability. These characteristics invite potential applications in optoelectronic devices, visible light communication, tumor therapy, biological imaging and other fields. There are a variety of CDs according to the different starting materials and synthesis routes. In this paper, we will systematically review nitrogen-doped CDs synthesized from citric acid and urea as the main precursor materials in our group in recent years, discuss their physicochemical properties, explore the methods and principles of CDs energy band regulation, and introduce the application progress of CDs.
2020, 13(5): 919-935.   doi: 10.37188/CO.2020-0037
Abstract(391) FullText HTML(152) PDF 4616KB(104)
Abstract:
Optical Coherence Tomography (OCT) is a new imaging technique that uses interference in low coherent light by measuring the delay and magnitude of backscattered or reflected signals from the sample. OCT technology can provide real-time structural information with one-dimensional depth and two- and three-dimensional tomography at micron-scale resolution. Besides its high spatial resolution, OCT imaging is beneficial for its non-contact and non-invasive methodology. The system is also easy to operate and relatively portable. OCT technology is mainly applied in the biomedical imaging field for diagnoses, making up for the shortcomings of the low penetration depth in confocal microscopes and the low resolution in ultrasonic imaging. At present, OCT technology has been used as the clinical standard for the diagnosis of retinal diseases, and the combination of OCT technology and endoscope technology has become an important tool for the clinical diagnosis of cardiovascular and gastrointestinal diseases. It also provides references for early cancer diagnosis, surgical guidance and postoperative rehabilitation of musculoskeletal diseases. To broaden the application of OCT technology and improve its medical detection capabilities, researchers are committed to increasing the penetration depth of OCT imaging in biological tissue, improving the system's resolution and signal-to-noise ratio, and optimizing its overall performance. This review introduces the principle and classification of OCT systems, their applications and their recent progress in various biomedical fields.
2020, 13(5): 936-964.   doi: 10.37188/CO.2020-0010
Abstract(305) FullText HTML(114) PDF 4187KB(53)
Abstract:
This paper comprehensively discusses all kinds of modern scientific and technological detection methods for paper raw materials, inks, inkpads, and pigments used in ancient paper cultural relics, including imaging and spectrometric technologies. Relevant imaging methods include photography, tomography and microscopic imaging methods. Photographic methods include light transmission, infrared, ultraviolet, X-ray and neutron activation photography to display macroscopic information on a sample’s surface or inside. Tomography methods include X-ray, terahertz, and optical coherence tomographic methods to display layered information beneath the sample’s surface. Microscopic imaging methods include optical, scanning electron, transmission electron and atomic force microscopic imaging methods to display the sample’s microscopic information. Spectroscopy methods with fingerprint characteristics based on the principles of wave-matter interactions include chromatography, mass spectrometry, electron paramagnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, X-ray fluorescence spectrum, molecular fluorescence spectrum, Raman spectrum, UV-Vis-NIR-MID-THz absorption spectrum and hyperspectral methods. It shows that the comprehensive applications, complementary advantages and mutual confirmations of the above technologies are powerful means to reveal important traits of paper cultural relics, such as one’s manufacturing process, artistic features, preservation history, disease status, authenticity, method of reparation, etc.
2020, 13(4): 647-659.   doi: 10.37188/CO.2019-0241
Abstract(1052) FullText HTML(367) PDF 1212KB(116)
Abstract:
Ultrafast laser technology is one of the most active research frontiers in lasers, physics and information science. It is widely applied in industrial processing, biomedicine, lidar and other fields. Because of their unique physical structure and excellent photoelectric properties, two-dimensional materials have a wide operating band, controllable modulation depth and short recovery time when they are employed as saturable absorbers in ultrafast lasers. Among them, transition metal dichalcogenides have become a focus of research because their band-gap is continuously adjustable. In this paper, we introduce the characteristics of transition metal dichalcogenides and the fabrication methods of saturable absorber devices. The research progress of ultrafast lasers based on emerging transition metal dichalcogenides is reviewed, and the development trend is highlighted.
2020, 13(4): 660-675.   doi: 10.37188/CO.2019-0231
Abstract(672) FullText HTML(322) PDF 8130KB(72)
Abstract:
The advanced light source represented by the new generation of the diffraction limit synchrotron radiation source and the full-coherent X-ray free-electron laser has become an indispensable research tool in many fields. The continuous development of advanced light sources drives the rapid progress of ultra-precision optical manufacturing. The surface precision of a K-B mirror, a key focusing optical element in advanced light sources, is an important factor, which should be less than tens of nano radians. However, high precision K-B mirror surface metrology still has great technical challenges and is now a research hotspot in the scientific community. This paper introduces typical K-B mirror surface metrology, including reflection profile measuring technology such as the Long Trace Profiler (LTP), the Nanometer Optical component Measuring (NOM), and stitching interference metrology. Current K-B mirror surface shape technologies are summarized and the upcoming research progress is prospected.
2020, 13(4): 676-694.   doi: 10.37188/CO.2019-0208
Abstract(640) FullText HTML(311) PDF 4354KB(77)
Abstract:
High power continuous-wave ytterbium-doped fiber lasers have unique advantages such as high electro-optical efficiency, excellent beam quality and good thermal management. For these reasons, these fiber lasers are widely used in industrial processing, national defense and military, and scientific research. However, their non-linear and thermal effects at high-power conditions limit the further improvement of their output power. In this paper, the formation mechanism and corresponding suppression methods of stimulated raman scattering and thermally induced mode instability are analyzed. We hope that these analyses can provide some reference for the design and integration of high-power fiber laser systems. The research results for overcoming these limited factors introduced since 2015 are then discussed in detail. This paper is concluded by predicting the development prospects of high-power continuous-wave ytterbium-doped fiber lasers.
2020, 13(4): 695-704.   doi: 10.37188/CO.2020-0052
Abstract(349) FullText HTML(171) PDF 1380KB(41)
Abstract:
Fiber-reinforced silicon carbide composites with excellent mechanical and thermal properties are widely used in aerospace, nuclear energy, automobile, chemical industry and many other fields, especially in optical mirrors. This paper introduces the characteristics of fiber-reinforced silicon carbide composites. The advantages and disadvantages of different preparation processes of fiber-reinforced silicon carbide composites are compared. The protective effects of different interface layers on fibers and composites are expounded. The application progress of fiber-reinforced silicon carbide composites in the field of optical mirrors at home and abroad is summarized. Finally, the research direction to be carried out for realizing large-scale application of fiber-reinforced silicon carbide mirror blanks is analyzed.
2020, 13(3): 427-441.   doi: 10.3788/CO.2020-0028
Abstract(1891) FullText HTML(797) PDF 2774KB(155)
Abstract:
All-solid-state deep ultraviolet coherent light sources have important applications in frontier science, high technology and many other fields. An effective and feasible technical approach is to use commercially available visible and near-infrared all-solid-state lasers as the fundamental frequency light source to generate a deep ultraviolet laser through cascaded frequency conversion using nonlinear optical crystals. This paper reviews the research progress of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet coherent light sources. Taking KBBF crystals as the representative example, their discovery, crystal growth, corresponding prism-coupled device technology, main optical properties, and ability to generate deep ultraviolet coherent light are each introduced. It was proven that KBBF crystals are excellent nonlinear optical crystals that can achieve deep ultraviolet laser output through direct frequency doubling. The applications of deep ultraviolet coherent light sources based on KBBF crystals and prism-coupled technology are discussed, with special focus given to ultra-high resolution photoelectron spectrometers. Finally, the future direction of the development of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet laser technology are given.
2020, 13(2): 217-228.   doi: 10.3788/CO.20201302.0217
Abstract(1515) FullText HTML(826) PDF 3187KB(193)
Abstract:
In recent years, OLED(Organic Light Emitting Diode) devices have been widely used in small-and medium-sized displays, and have gradually been popularized in large area display applications, such as in TVs and lighting. With the continuous development of organic light-emitting technology, higher requirements drive research on the color and pattern of OLED devices. Compared with the traditional vacuum evaporation process, inkjet printing technology easily colors large-area devices and patterns composite functional materials. It is also simple to implement, low in cost and has a more flexible process. In this paper, the current progress of inkjet-printed OLED devices is reviewed. Furthermore, this paper systematically introduces the development of inkjet printing equipment, by optimizing bank structures to improve the resolution of their display screens, by optimizing the ink formulation and composition ratio to suppress the coffee ring effect of inkjet droplets, and improves the uniformity of display luminescence. Finally, this paper summarizes and provides prospects for the future development of this technology at home and abroad.
2020, 13(2): 229-248.   doi: 10.3788/CO.20201302.0229
Abstract(1462) FullText HTML(735) PDF 4890KB(72)
Abstract:
Laser technology in rock removal is an important research direction in the field of applied optics. It is a complex, high-temperature and high-pressure physical and chemical process with multi-phase, multi-coupling and multi-scale applications. In order to clarify the core difficulties in laser-rock interaction research and to provide an effective theory reference and trend information for researchers, an overview of research on laser rock removal technology is summarized. Firstly, the mechanism of rock removal using lasers is clarified. Then, existing research of laser rock removal is summarized and analyzed from different perspectives, including laser equipment for petroleum drilling and completion, its influencing factors, the phase-change heat transfer of temperature fields, its physical and mechanical properties, and its feasibility in the oil and gas industry. Finally, the advantages of rock removal by laser technology compared with traditional drilling and completion methods are elaborated. In view of the existing problems in laser-rock interaction research, the future development trend of rock removal by laser technology is predicted. The research results show that rock removal by laser technology can lead to research breakthroughs in field-supporting facilities, multi-factor evaluation, multi-field coupling mechanisms and theoretical systems of underground applicability.
2020, 13(1): 1-13.   doi: 10.3788/CO.20201301.0001
Abstract(1007) FullText HTML(501) PDF 2481KB(43)
Abstract:
In order to improve the responsivity and reduce the noise equivalent power of Field-Effect Transistor (FET) THz detectors, a suitable planar antenna structure is necessary.In this paper, we investigate the research progress of FET THz detectors integrated with planar antenna structures. Firstly, we analyze the working principle of FET THz detectors and clarify that an integrated planar antenna could effectively improve the detector's performance by enhancing its coupling efficiency with terahertz waves. Secondly, we present some typical planar antennas and discuss their pros and cons. These include the dipole antenna, the patch antenna, the slot antenna, the grating-gate, and others, which are each compared with respect to responsivity for the detectors. Finally, we find that the responsivity of the FET THz detectors can be greatly improved when applying planar antenna structure and that each type of antennas contributes uniquely. This work introduces several planar antennas integrated into FET THz detectors, including the performance and research progress of various antennas.Some existing problems are described and some predictions of the future development trends for this technology are summarized.
2020, 13(1): 14-27.   doi: 10.3788/CO.20201301.0014
Abstract(1325) FullText HTML(745) PDF 4222KB(80)
Abstract:
Quantum dots (QDs) have received widespread attention because of their adjustable emitted wavelength of light, color purity and high quantum efficiency, which have great potential in applications requiring high-color-quality displays with photoluminescence. In this paper, the progress of QD backlights based on each QDs on-chip, QDs on-surface and QDs on-edge are reviewed, including their principle, structures and current applications. Then, several other novel QD backlight structures are also introduced, prompting a proposal for two novel QD backlight technologies. One is the QDs scattering diffusion plate, which is prepared by injecting molding with a mixture of QDs and polymer at a low temperature. The other is a QD microstructure light guide plate, which is fabricated by transferring QDs on the surface of a light guide plate through screen printing or inkjet printing. Both of these two QD plates can achieve high color gamut while being simple to process, being low in cost and holding high production efficiency. These have wide applications in high color gamut liquid crystal displays.
2020, 13(1): 28-42.   doi: 10.3788/CO.20201301.0028
Abstract(1905) FullText HTML(1150) PDF 2768KB(169)
Abstract:
The semiconductor industry is the backbone of the high-tech and information age. Lithography technology, one of the core technology of the semiconductor industry, has become a key research subject all around the world. This article mainly discusses the light source of 13.5 nm Extreme Ultraviolet Lithography (EUVL) by using Laser-Produced Plasma (LPP). It makes a brief introduction to the principles behind this technology and the development history of this field at home and abroad. The introductions include the materials used in the multilayer mirror, and rationale for the selection of materials, the shape and design of the target and the type of laser. At the same time, this article points out that the main problems for the EUVL are light debris reduction and the conversion efficiency improvement of EUV light.This paper also gives special analysis of the light source output devices of 13.5 nm EUVL machines produced by international famous companies——Gigaphoton of Japan and ASML of the Netherlands, which can generate more than 100 W level EUV power. Finally, this article summarizes and forecasts future research related to this technology.
2020, 13(1): 43-61.   doi: 10.3788/CO.20201301.0043
Abstract(1052) FullText HTML(611) PDF 8834KB(101)
Abstract:
Emerging optical devices demand miniaturized, integrated and intelligent optical zoom systems, thus stimulating development in nano-optoelectronics. Metalenses are two-dimensional planar structures with lens function composed of arrays arranged specifically to equally focus wavelengths of light. Due to their ultrathin and lightweight properties and their ease of integration, it is expected that they will revolutionize optics by replacing the conventional bulky, curved lenses used that pervade optical devices. However, once the micro/nano-structures of a metalens are fabricated, their shape and size cannot be modified, which can not realize the real-time adjustment of focusing and will limit the further development of metalenses' functions and applications. Currently, substantial effort is being devoted to solving this problem. One of the most attractive aspects of metalenses is in the way they combine metasurface lenses with smart materials. In this article, we first provide an overview of novel tunable metalenses. Then, we elaborate and analyze their regulatory principles and device performance, respectively. Finally, we summarize the current problems and difficulties facing the development of tunable metalenses and describe the direction of their future development.
2020, 13(1): 62-74.   doi: 10.3788/CO.20201301.0062
Abstract(1247) FullText HTML(649) PDF 6598KB(71)
Abstract:
Silicon-based photodetectors have been widely investigated due to their high reliability, easy integration and low cost. With the development of artificial intelligence and autonomous vehicles, research and performance enhancement of silicon-based photodetectors is an important field of research. Quantum dots are excellent light-conversion and light-modulation materials due to their superior absorption coefficient, tunable spectra, high photoluminescence quantum yield and simple integration. The tunable light absorption and phototuminesence properties of quantum dots make them suitable materials for enhancing the detection. Quantum dots enhanced silicon-based photodetectors are emerging as a new technique to advance the performance of detection and imaging. In particular, they show potential to expand the functionality of CCD and CMOS devices and further satisfy increasing demands for detection. In this review, we summarized the progress of quantum dot-enhanced silicon-based photodetectors in the field of ultraviolet detection, infrared imaging, polarization detection and spectral detection, hoping to attract the attentions of domestic colleagues.
2019, 12(4): 731-740.   doi: 10.3788/CO.20191204.0731
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Abstract:
Optical coherence tomography(OCT) has become a hot research topic in the field of clinical medicine due to its features including micron-level high resolution, non-invasive imaging and instantaneity, which has developed rapidly and made much progress and break throughs in recent years. In this paper we briefly review the applications of OCT in ophthalmology, discuss the methods of speckle noise reduction in the spatial and frequency domains of OCT images, and summarize the precise positioning and stratification method of each layer of tissue in the OCT anterior segment and retina image. The advantages and disadvantages of the segmentation methods based on gray value search, active contour model, graph and pattern recognition algorithms are analyzed and compared. In addition, the existing problems with segmentation methods are discussed and the corresponding solutions and feasible optimization schemes are proposed. Analysis and evaluation of clinical diagnostic indicators of ophthalmic diseases are discussed. According to the needs in ophthalmology and the current status of OCT image processing, the development trends and level of OCT image processing are discussed and analyzed.
2019, 12(4): 719-730.   doi: 10.3788/CO.20191204.0719
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Abstract:
Different kinds of modulation methods are usually adopted when physical quantities, such as temperature, forces and deformation, are measured in interference. Fringe patterns carry measurement information of those quantities and are usually later analyzed for its retrieval. Single closed fringes are generally what is recorded by CCD. When the experimental conditions are not conducive to phase shifting, loading wave and other modulation means, the regularized phase tracking(RPT) technique can retrieve a continuous phase map directly from a single interferogram, making it the most effective method. In recent years, RPT technique has been improved to achieve higher processing power, algorithm robustness and retrieval accuracy for complex fringe patterns, ultimately making it more practical. In this paper, we introduce the basic algorithm principle and how the RPT technique is applied in the retrieval of single interferograms, review the technique's relevant modifications and developments in recent years, cite some examples used for phase retrieval and speculate the direction of its future development.
2019, 12(4): 701-718.   doi: 10.3788/CO.20191204.0701
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Abstract:
In order to meet the demand for single-photon Rydberg excitation of cesium atoms in the field of atomic physics, we investigated the key technolgies of single-frequency continuous wave(CW) tunable ultraviolet(UV) laser at 318.6 nm. Combining the fiber lasers, fiber amplifiers and the nonlinear crystals, we achieved 318.6 nm UV laser over 2 Watt output with cavity-enhanced second-harmonic generation following the sum-frequency generation of two infrared lasers at 1 560.5 nm and 1 076.9 nm in PPLN crystal. The typical root-mean-square fluctuation of UV laser power was less than 0.87% within 30 minutes. The electronic side-band locking scheme based on a temperature controlled hyper-fine ultra-stable ultra-low-expansion cavity placed in an ultra-high vacuum chamber was used to achieve the continuously tuning of UV laser in a wide range while still keeping it locked. The continuously tunable range was larger than 4 GHz and the residual frequency fluctuation of UV laser was about 16 kHz. We employed this high-power single-frequency continuously tunable UV laser system for the direct 6S1/2nP3/2(n=70-100) Rydberg excitation of cesium atoms with atomic vapor cells in experiments. After that, relevant theoretical analysis and research have been done. With a magneto-optical trapped cesium atomic ensemble, single-photon Rydberg excitation using the UV laser system was achieved with a pure optical detection scheme.

Sponsors: the Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP), CAS and Chinese Optical Society (COS)

ISSN 2095-1531

CN 22-1400/O4

CODEN ZGHUC8