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Abstract(167) FullText HTML(60) PDF 1246KB(13)
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Owing to the strong penetrating ability in the atmosphere, 532 nm-wavelength green laser has wide applications including free-space optical communications and laser three-dimensional mapping. A spectral filter, with a half-power bandwidth of less than 100 pm, is an important optical element to suppress the interference of background light. Therefore, an ultra-narrow band-pass filter based on optical interference film is designed and fabricated in this paper. The high and low refractive index film materials are Tantalum pentoxide (Ta2O5) and Silicon dioxide (SiO2), respectively. The designed optical thin films are deposited on a fused quartz substrate by double-ion-beam sputtering deposition method. The transmission spectrums of the filters are measured by a tunable laser and a power meter. The half-power bandwidths of the filters are 60±2 pm, and the transmittance reaches 62.6%.
Abstract(20) FullText HTML(9) PDF 1216KB(0)
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Averaged intensity and spectral shift of partially coherent chirped optical coherence vortex lattices (PCCOCVLs) in biological tissue turbulence are investigated, where optical lattice structures in monochromatic optical field and spectral rapid transitions in polychromatic optical field are stressed. It is found that the beam profile evolves from annular structure with vortex core into a periodic array of lobes with dark zone, and it finally present a Gaussian-like pattern in biological tissue. Although lattice parameter modulates beam profile, it cannot affect spectral behavior in biological tissue turbulence. The analysis of spectral shift also shows that a smaller distance is beneficial to spectral rapid transition, where the transverse coordinate decreases with an increase of chirp parameter and a decrease of pulse duration. The accumulated turbulences in a longer distance can suppress not only spectral transition, but spectral shift. The reduction of spectral shift is accompanied by a stronger biological tissue turbulence. The results have the application possibility in image recognition, medical device and noninvasive optical diagnose in biological tissue.
Abstract(12) FullText HTML(3) PDF 1251KB(0)
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In present manuscript, we introduce the prepared Ag@SiO2 nanostructure directly into tellurite luminescence glass 70TeO2-25ZnO-5La2O3-0.5Er2O3. We find that the maximum enhancement of visible and infrared excitation spectra intensity of (A) Ag(1.6×10−6 mol /L)@SiO2(40 nm) @Er3+(0.5%):tellurite glass relative to (B) Er3+(0.5%):tellurite glass is about 149.0% and 161.5% respectively. Their maximum enhancement of visible and infrared luminescence spectra intensity is 155.2% and 151.6%, respectively. We also find that sample (A) has a large increase for lifetime compared with sample (B). Because surface plasmon absorption peak of Ag@SiO2 is located just at 546.0 nm, it completely resonates with the luminescence peak of erbium ion at 546.0 nm. Therefore, the resonance enhancement action of Ag@SiO2 on the luminescence of erbium-doped tellurite luminescence glass is obvious. The Ag@SiO2 nano core-shell structure studied in present paper is pre-fabricated in advance. Thanks to advantages of the step-by-step realization of the silver nano core-shell structure and the production of glass: it can successfully smoothly control the size of Ag@SiO2, it also has the advantage of strong operability in the manufacturing process of Ag@SiO2@Er:telluride luminescence glass. It also has the advantages of low price and minor cost. Moreover, it can not only ensure that the silver is not oxidized, but also it can successfully control the distance between the rare earth ion luminescence center and the silver surface plasma, and it can also successfully reduce the back energy transfer, therefore which promotes the silver surface plasma to more effectively enhance the intensity of photo-luminescence. These results are of great significance for enhancing the luminescence intensity of rare earth luminescent materials and promoting their wider application prospects.
Abstract(21) FullText HTML(6) PDF 4758KB(3)
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With the development of optoelectronic countermeasures and ultrashort pulse laser technology, the study of the interaction between ultrashort pulse laser and monocrystalline silicon has very important theoretical and practical significance. However, there are few reports about the damage effect of 532 nm picosecond pulse laser on monocrystalline silicon. Therefore, in order to further clarify the damage mechanism of 532 nm picosecond pulsed laser to monocrystalline silicon, we have carried out an experimental study to measure the damage threshold, clarify the damage mechanism, and discuss the pulse accumulation effect at low flux. Firstly, using a laser with a wavelength of 532 nm, a pulse width of 30 ps and a metallurgical microscope, based on the 1-on-1 laser damage test method, the zero damage probability threshold is determined to be 0.52 J/cm2.Secondly, the damage effect of picosecond laser irradiated monocrystalline silicon was studied under different laser flux, and it was found that the damage of 532 nm picosecond laser to monocrystalline silicon is manifested as heated-effect damage and plasma impact damage. The increase of energy density can be divided into three stages according to the main damage mechanism: thermal effect (0.52~3 J/cm2), thermal ablation (3~50 J/cm2) and plasma effect (>50 J/cm2), and the damage areas are corresponded to different growth laws with the laser energy density, respectively. Finally, an experiment of multi-pulse cumulative effect was carried out at low laser flux, and it was found that at a laser energy density of 0.52 J/cm2, the surface was irradiated continuously for 16 shots.The formation of a heat-affected zone confirms that the cumulative effect of multiple pulses can lower the laser damage threshold of monocrystalline silicon.
Abstract(164) FullText HTML(70) PDF 4336KB(9)
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The technology of enhancing fluorescence emission can increase the sensitivity of fluorescence detection and the brightness of LEDs, and is of great significance in improving the performance of light-emitting devices. Since the metal structure has a good effect in enhancing the local field and enhancing the fluorescence emission, and the flexible dielectric material has flexible bendability characteristics, for the enhancement of the fluorescence emission, this paper proposes a flexible structure composed of metal-dielectric-metal (MDM). The influence of the structure on the directional emission enhancement of quantum dots is systematically studied by using the finite difference time domain method. Theoretical calculations show that the local undulations and arcs of the flexible MDM structure promote fluorescence enhancement, and can increase the quantum efficiency of the quantum dots located at the center of the structure by about 7 times. And the refractive index and thickness of the dielectric can be changed to achieve the tunability of the target wavelength. At the same time, the experimental verification shows that the flexible MDM structure does have a positive effect on the fluorescence enhancement. This discovery is useful for future display technologies and flexible light-emitting devices. It is of great value and has certain guiding significance for the development and application of high-efficiency flexible devices.
Abstract(35) FullText HTML(16) PDF 4728KB(9)
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With the advantages such as simple structure, simple process and easy interface control, the photoelectric devices based on carbon nanomaterial/bulk semiconductor van der Waals (vdW) heterojunctions can fully utilize the ultrahigh carrier mobility of carbon nanomaterials and the excellent photoelectric properties of bulk semiconductors. Especially, the novel mixed-dimensional vdW heterojunctions with atomic-level interfaces, whose bandgaps are matched with those of bulk semiconductors, can be formed by controlling the diameter/chirality and Fermi level of single-walled carbon nanotubes (SWCNTs). Here, we reported a self-powered broadband photodetector based on the p/n vdW heterojunctions by combining (6, 5)-enriched semiconducting SWCNT film with n-type GaAs, and used graphene to reduce the probability of carrier recombination in SWCNT film and to promote the carrier transport. The experimental results suggest that the self-powered device exhibits high-sensitivity photoelectric response toward the incident photons in the 405−1064 nm range, and that the max photoelectric responsivity of 1.214 A/W and the specific detectivity of 2 × 1012 Jones could be achieved at zero bias.
Abstract(272) FullText HTML(98) PDF 7268KB(36)
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Helmholtz-Kohlrausch effect (H-K effect) described the influence of color purity on the perceived brightness of a color object. Quantum dots (QD) based backlights can enhance the color quality of liquid crystal display (LCD) display with improved perceived brightness due to the well-known H-K effect. However, the H-K effect of QD embedded TV (also known as QLED TV) has not been fully demonstrated. In this paper, we investigated the H-K effect of QLED TV through a comparative study between QLED backlights and YAG-LED backlights. By comparing the viewers’ experimental results with the Kaiser and Nayatani model, we demonstrate that QLED TV shows significant H-K effect. To achieve the same perceived brightness with YAG-LED TV, the physical brightness of QLED TV was greatly decreased to 75% for pure red color, 86% for pure green color, and 74-88% for bright colorful images. Moreover, QLED TV is much preferred than the YAG-LED TV even when both QLED TV and YAG-LED TV show the same perceived brightness. The results imply the bright future of QLED TV toward health display.
Abstract(49) FullText HTML(7) PDF 4690KB(20)
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Adaptive optical correction technology can effectively improve the beam quality of solid slab lasers, but with the increase of laser output power, the output beam aperture and the system volume gradually increase, which makes the design of adaptive optical correction systems difficult. Therefore, under the premise of meeting the requirements of conjugate detection in the adaptive optical correction system, it is of certain research significance to optimize the size parameters of the detection system as a whole, and realize the detection of multiple parameters such as wavefront phase and beam quality. In this paper, we achieve the multi-parameter detection of a 160 mm×120 mm rectangular beam emitted by a slab laser when the overall size of the system is 350 mm×180 mm×220 mm (length × width × height). According to the technical requirements of large detection apertures, there are limitations in tube length and long exit pupil distance. Firstly, the dual-Gaussian initial structure was used to eliminate the aberration. Combined with the aspheric surface technology, the design scheme of splitting detection after high-ratio beam compression was adopted to achieve the simultaneous detection and evaluation of multiple parameters. Secondly, the initial parameters of the system were determined based on the principles of telephoto imaging and conjugate imaging. Thirdly, the simulation model of the detection system was established to analyze the imaging quality and the tolerance of the system, which were carried out to provide the basis for the construction of the experiment. Finally, the experiments were built to verify the design results. Results indicate that the conjugate wavefront detection, light intensity uniformity detection and beam quality evaluation of a 160 mm × 120 mm rectangular beam can be realized under the object-image conjugation and size constraint conditions. In the experiment, the β factor of the measured beam is 1.24 times the diffraction limit, and the uniformity is 73.8 %, which meets the technical requirements.
Abstract(21) FullText HTML(8) PDF 3751KB(2)
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To improve the accuracy and efficiency of dynamic speckle metric for nondestructive detecting the far-field target hit-spot intensity in target-in-the-loop (TIL) system, a multi-channel cooperative detection system for acquiring speckle signals is established. And the theory of dynamic speckles, the simulation model of this system and the spatial-temporal spectral fusion characteristics are investigated. As a first step, the power spectrum is obtained by filtering, auto-correlating and Fourier transforming the intensity fluctuations of dynamic speckle detected by the point detector. Then, the feasibility of speckle-metric, obtained by multiplying the spectrum with weights, is explored to monitor the target-focused spot. As a second step, the approach of splicing the temporal signals obtained from different spatial locations on the receiving plane is proposed. Moreover, the prerequisites of this approach are listed. Finally, the effectiveness of the proposed speckle metric obtained by fusing spectrum is verified through simulations and experiments. The results show that speckle metric decreases with the increase of the hit-spot size, and four-channel space-averaging metric can improve the accuracy by 2 times when each group of signals is uncorrelated. Besides, the metric obtained by spatial-temporal fusion spectrum not only guarantees accuracy but also increases the system bandwidth by 4 times. Therefore, the multi-channel cooperative acquisition of speckle metric can monitor the hit-spot change of far-field moving target more rapidly.
Abstract(45) FullText HTML(17) PDF 3948KB(4)
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Dual-wavelength retinal imaging adaptive optics systems are suitable for high contrast and resolution imaging of retinal capillaries. The compensation of the longitudinal chromatic aberrations (LCAs) is considered. The LCA is measured, the measured wavefronts are analyzed, and the arbitrary wavefront LCA compensation method is given. An adaptive correction experiment is done, and the root mean square error of the wavefront is reduced to 0.16 λ (λ=589 nm) and the retinal capillary resolution is improved to 6 μm. This work may be used for the clinical applications of retinal imaging.
Abstract(46) FullText HTML(11) PDF 4370KB(10)
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Accurate measurement of three-dimensional attitude Angle is widely used in aviation, aerospace, national defense and other fields. In order to realize the measurement of three-dimensional attitude Angle conveniently and accurately, an optical system based on lens array is designed and an analysis model of micro-three-dimensional attitude Angle measurement is established in this paper. In the system, the collimated parallel beam passes through four array lenses arranged in a pyramid shape to form regular array spots on the CCD. By analyzing the distance between the spots of CCD imaging, the distance between the adjacent aperture on the lens array and the inclination Angle between the lens array and CCD, the beam pitch Angle and azimuth Angle relative to the receiving system can be obtained. By using the Angle between the lines of the array spots relative to the horizontal or vertical plane, the roll Angle about the Z axis can also be obtained. Compared with the measurement results of the high-precision autocollimator, the measurement accuracy of the proposed method is verified to be RMS≤0.1 ", and the results show that the proposed method can realize the measurement of three-dimensional attitude Angle.
Abstract(38) FullText HTML(21) PDF 4075KB(3)
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Objetive   In order to allow subjects to detect various physiological parameters under non-contactconditions in daily life.  Method  A method based on imaging photoplethysmography has been proposed to estimate physiological parameters from face videos recorded by mobile phone in this paper. First, the "wavelet transform-principal component analysis-blind source separation" algorithm is proposed to extract the RGB three-channel pulse wave signal with high signal-to-noise ratio. Then, the green channel signal is processed separately in the frequency domain and the time domain to estimate the heart rate and respiration rate;the pulse wave signals of the red and blue channels are processed, and then combined with the oxygen saturation detected by the oximeter to perform data fitting, and the best linear equation for estimating the oxygen saturation value from the facial video is found. Finally, the error of the estimation results of various physiological parameters under natural light is compared, and the estimation results of each parameter under three lighting environments are analyzed.  Result  The results show that under the three lighting environments, the average error of heart rate is 0.5512 bpm, the average error of respiration rate is −0.6321 brpm, and the average error of oxygen saturation is −0.2743%.   Conclusion  In summary, the non-contact physiological parameter estimation method proposed in this paper has high accuracy, universality and stability, and the estimation result is highly consistent with the measurement result of the standard instrument, which can meet the needs of daily physiological parameter measurement.
Abstract(127) FullText HTML(52) PDF 3651KB(7)
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A high-sensitivity surface plasmon resonance (SPR) sensor comprising an eccentric core ten-fold photonic quasi-crystal fiber (PQF) with a D-shaped structure and coated with indium tin oxide (ITO) is designed and analyzed numerically. The eccentric core D-shaped structure makes analysis of liquids more convenient and also strengthens the coupling between the core mode and SPP mode to improve the sensing sensitivity. The characteristics of the sensor are investigated by the finite element method (FEM). The wavelength sensitivity increases with increasing refractive indexes (RIs) and the maximum wavelength sensitivity and resolution are 60000 nm/RIU and 1.67×10−6 RIU, respectively. The sensor delivers excellent performance and has large potential applications in measurement of liquid refractive indexes.
Abstract(73) FullText HTML(28) PDF 5699KB(16)
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Optical Systems using aspheric components (especially for free-form ones) have remarkable advantages over traditional spherical systems that they can realize complicated requirements with simple optical-mechanical structure relying on abundant optional design parameters. Surface testing is an essential process for the ensurance of accuracy in manufacture. Therefore, plenty of testing methods have been developed to meet varying testing demands of different types of surface or different stages in manufacture. This paper retrospects the history of aspheric surface testing technology, classifies available techniques by the criterion of the using interferometry or not, then introduces corresponding technical indexes, applicable conditions, research progress as well as application cases.This paper highlights the high-precision interferometric methods, illustrate basic principles, optical layouts as well as testing performances of every method classified into Null and Non-null testing. The pros and cons of each method are compared, some relative algorithms are explained and precise adjustment methods of testing path are discussed.
Abstract(90) FullText HTML(36) PDF 5337KB(8)
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Objetive   In order to obtain the true optical characteristics of the Digital Micro-mirror Device (DMD), a test method for the stray light distribution of the micro-mirror unit was proposed, and an experimental device was built to test the stray light distribution of the micro-mirror unit in the 2×2 array area.   Method  First, a stray light test method is proposed. Then, in view of the small size of the micro-mirror unit and the flexible configuration mode, an illumination system with continuously adjustable convergent spot size and an imaging system that can clearly image the micro-mirror unit were designed. Finally, the stray light distribution of the micro-mirror unit in the 2×2 array area is obtained through experiments.   Result   The test results show that the reflection energy near the center channel of a single micro-mirror unit is strong, while the reflection energy near the edge is relatively weak. In addition, the micro-mirror unit also reflects part of the energy outside the test area. The maximum absolute stray light intensity of the micro-mirror unit in the test area appears near the central channel, and its gray value is 6.86. The maximum absolute stray light intensity of the micro-mirror unit close to the test area also appears near the central channel, and its gray value is 4.01, which indicates that the stray light near the central channel is strong. The relative intensity of stray light in the test area is relatively weak, which increases sharply from the edge of the test area and reaches the peak value of 293.5% after about two micro-mirror units, and then decreases sharply.   Conclusion  The above research results can play a certain guiding role for the development of various instruments using DMD in the future.
Abstract(53) FullText HTML(25) PDF 4496KB(2)
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In order to correct the measurement error caused by glass medium in high temperature deformation measurement, this paper takes glass medium as a part of camera calibration model. Based on photogrammetry technology and digital image correlation method, a binocular camera calibration method in complex environment is proposed and applied to high temperature deformation measurement. Firstly, aiming at the calibration difficulty caused by the poor image quality in complex environment, the camera imaging model with distortion correction is adopted to complete the binocular camera calibration by bundle adjustment camera calibration method, which improves the success rate and stability of calibration. Secondly, aiming at the problem of low calibration accuracy of binocular camera in complex environment, the influence of lens focal length, ambient light interference and the distance between glass and camera on the calibration results is analyzed, and the optimal calibration parameters are given, so that the calibration reprojection error is reduced from 0.832 pixels to 0.132 pixels. Finally, the measurement error of calibration with and without glass is compared by using the measurement environment with glass medium, which proves that this method can greatly reduce the measurement error. The test results show that this method can effectively reduce the measurement error of displacement field caused by glass medium in high temperature environment. The maximum decrease of measurement error of displacement field in X, Y and Z axes is 76.26 %, 75.02 % and 42.02%, respectively. The method in this paper can achieve high-precision camera calibration in complex environments, and has good calibration stability. It is an effective way to realize accurate measurement of high temperature deformation.
Abstract(74) FullText HTML(77) PDF 3743KB(37)
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Electro-optic modulators based on lithium niobate (LiNbO3, LN)thin film platform have the advantages of small volume, high bandwidth and low half wave voltage. They have important application prospects in the field of optical fiber communication and optical fiber sensing, and thus become a heavily researched topic in recent years. In this paper, the research progress of waveguide structure, coupling structure and electrode structure of LN thin film modulator is reviewed in detail.The fabrication process of LN thin film waveguide is summarized, and the performance of different modulator structures is analyzed. Based on SOI and LNOI platform modulator is realized VπL<2 V∙cm, bilayer inversely tapered coupling scheme achieves coupling loss <0.5 dB/facet, traveling wave electrode structure achieves modulation bandwidth >100 GHz. Thin film LN modulators are better than that commercial LN modulators in most aspects. It can be predicted that in the near future, with the further improvement ofwaveguide technology, thinfilmLN will become a popular scheme of LN modulators. Furthermore, the potential directions for the future of their research are proposed.
Abstract(21) FullText HTML(13) PDF 5919KB(3)
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In order to improve the detection efficiency of micro array electrodes (MAE) and reduce the production cost, a technology combining digital micromirror device (DMD) maskless projection lithography with electrochemical deposition was proposed. Firstly, a user-defined micro structure array was fabricated by using the advantages of PZS high resolution motion and DMD flexibility. And a uniform Au micro array electrode (Au/MAE)was fabricated by electrodeposition. Then, the electrochemical properties of Au/MAE with different structures were compared by cyclic voltammetry, and the optimized structural parameters were obtained. Finally, the current response of optimized Au/MAE to glucose with different concentrations and pH values were studied, and the anti-interference of Au/MAE in glucose detection was tested by chronoamperometry. Electrochemical analysis shows that the simple Au/MAE has a significant amperometric response and strong anti-interference ability for the electrochemical detection of glucose with a sensitivity of 101 μA·cm−2·mM−1. This method has the advantages of high resolution, high consistency, simple process and low cost, which provides a feasible operation scheme for the fabrication of biosensor array.
Abstract(214) FullText HTML(94) PDF 4455KB(13)
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When a micro-milling tool has a clamping angle on its spindle, the wear of the tool edge will accelerate and shorten the tool’s lifespan. In order to accurately observe the inclination state of the micro-milling tool on the machine, a three-dimensional pose reconstruction method based on the depth of field of a micro-milling tool is proposed. The laser coaxial digital holographic experimental device is used to obtain the micro-milling tool hologram, and the reconstruction image is obtained through the Fresnel reconstruction algorithm. The tool edge points are extracted as the key points in the reconstruction image, the wavelet transform local variance operator is used to obtain the degree of focus of the key points, and then the axial position corresponding to the milling tool is determined. The least square method is used to fit the key points and correct the reconstruction error, from which the three-dimensional pose reconstruction of the micro-milling tool is realized. The experimental results show that the reconstruction error of the micro-milling tool obtained by the three-dimensional pose reconstruction method is better than 0.1. This method can accurately measure a three-dimensional pose of a micro-milling tool, which can provide a reference for the subsequent correction of micro-milling tool clamping accuracy.
Abstract(90) FullText HTML(38) PDF 3720KB(9)
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Objetive  Ultraviolet detection technology has been widely used in various fields of human production and life. It is of great significance to study the system of ultraviolet (UV) imager with wide spectrum.  Method  Based on the theoretical formula of chromatic aberration, a scheme of correcting the chromatic aberration of the optical system of the wide-band UV imager with a single material was proposed. Combined with the performance index of the high-sensitivity dynamic UV imaging detector, the optical system of the 210−400 nm wide-band UV imager with only one lens material and all lenses being spherical was designed. The optical design software CODE V was used to optimize the system and evaluate the image quality.  Result  The results demonstrate that the modulation transfer function (MTF) in total fields of view and all waveband of the system is better than 0.6 at the Nyquist frequency of 40lp/mm and RMS<7.8 μm, the system has good imaging quality.  Conclusion  The system does not contain aspheric optical elements, which is not only easy to be processed and assembled, but also reduces the developing cost, and lays a technical foundation for the development of a wide spectrum UV imaging spectrometer.
Abstract(104) FullText HTML(41) PDF 4097KB(9)
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Objective  Haze at night has the characteristics of low contrast, non-uniform illumination, color cast and much noise. These cause nighttime haze removal from single image to be an ill-posed problem with challenges. In this paper, we put forward a method which can be properly applied to remove nighttime haze and improve image quality.   Method  The input image is first decomposed into glow layer and haze layer with a modified color channel transformation for glow artifacts and color correction. A new light segmentation function is proposed next by using gamma correction of channel difference and setting threshold levels as the probability of the pixel which belongs to light source regions. Then we estimate the ambient illuminance map combining maximum reflectance prior with the above probability and compute atmosphere light in the light and non-light regions. Finally, we establish a novel linear model to build the connection between the image depth map and three image features including luminance, saturation and gradient map for the light source regions while using the dark channel prior for the non-light source regions.   Result   The result of the light segmentation is 0.07, and the parameters of the linear depth estimation are 1.0267, −0.5966, 0.6735 and 0.004135.   Conclusion  Experimental results show our proposed method is reliable for removing nighttime haze and glow of active light sources, reducing much noise and improving the visibility.
Abstract(172) FullText HTML(84) PDF 5328KB(13)
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A visible/near-infrared real-time imaging spectrometer is designed for hyperspectral imaging. The spectrometer is designed on the basis of an acousto-optic tunable filter (AOTF). Its operating band range is 1.3 μm, in which the visible light camera works in the 400 nm−1000 nm band and the near-infrared camera works in 1000 nm−1700 nm band. A field-programmable gate array (FPGA) is used as the core processing unit of the spectrometer control system. The Cameralink interface is used to collect camera data, the AOTF frequency is controlled by the serial port. Through the organic combination of AOTF synchronization signal and the trigger signal outside the camera, the one-to-one correspondence between a continuous image and multi-wavelength cyclic acquisition is realized. Finally, the image data is transmitted to the upper computer through the USB3.0 interface for real-time display. The field test shows that the imaging quality of the spectrometer is good and the system works stably. For images with a 1024*1024 resolution, the real-time transmission rate of the image can reach up to 120 frame/s, which meets the design requirements. In practical engineering applications, the control system has a rich interface, high reliability, flexible interface and strong expansibility.
Abstract(155) FullText HTML(29) PDF 3675KB(26)
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The diffraction of optical fields is a universal phenomenon that can cause beams to spread during propagation in free space. Ideal non-diffracting (spatially stable) structured beams can propagate in free space without changing their initial field distribution at any plane orthogonal to the direction of propagation. Moreover, the non-diffracting structured beams also have the ability for self-recovery after encountering obstacles. Hence generating non-diffracting beams or structured beams is a very important field of research for overcoming the diffraction behavior of beams during propagation in free space. Any non-diffracting structured beams with a certain intensity, phase distribution, and propagation properties have special applications in the field of optics. Lately, some non-diffracting beams with complex structures are introduced one after another, such as Mathieu beams, parabolic beams, Lommel beams, asymmetric Bessel beams, and so on. The complex amplitude modulation is necessary to produce the nondiffracting beams with abundant structures. At present, no commercial optical modulator can modulate the phase and amplitude of light waves simultaneously. Based on binary computer-generated holography that can encode the two-dimensional transmission function distribution, a binary real amplitude computer-generated hologram with complex amplitude modulation functionality is designed and constructed. Binary real amplitude computer-generated holograms, which are a kind of binary optical diffracting element that generate non-diffracting beams with complex optical morphology, are designed and constructed by encoding the complex optical filed information by using the Lohmann-type detour phase coding method. For the Lohmann-type detour phase coding method, the coding principle is mainly that the complex field distribution information is transformed into amplitude and phase information. The complex field distribution is sampled, and one can obtain a matrix of point sources. Here, we extract the amplitude and phase information as input information to generate two 2D real value matrices for detour phase coding. By using the homemade projection imaging lithography system, the silver salt halide plate was exposed, developed and fixed, and then a binary mask is precisely machined. The homemade projection imaging lithography system can machine holograms with an ultrahigh resolution of 79, 874 × 79, 874 dpi and a maximum output of 156 mm × 156 mm. Using the mask, the non-diffracting beams with abundant structures can be produced accurately. Taking the nondiffracting Mathieu beam as an example, two kinds of binary real amplitude computer-generated holograms for generating Mathieu beams are constructed by using the Roman type detour phase coding method. In the process of the machine, the photolithography file is firstly divided into 47 unit patterns of 600 × 600 pixels, where each unit pattern is automatically inputted into a DMD (Digital micromirror) in proper sequence, and then subsequently scanned line-by-line for projection exposure. When the lithography is complete, the silver halide plate is processed to obtain the mask. In this experiment, the calculated CGH is 28, 000×28, 000 pixels, and the size of a pixel is 318 nm×318 nm. The size of the produced binary masks is 8.9 mm × 8.9 mm. The non-diffracting Mathieu beams with elliptic coefficient q=10 and topological charge number m=0, 1 are generated, which belong to the even type Mathieu beams of the first kind. Undoubtedly, the classes of nondiffracting Mathieu beams, including the even type Mathieu beams of the second kind, odd type Mathieu beams of the first kind, and odd-type Mathieu beams of the second kind can also be generated using the same encoding method and experimental setup. Since one can encode both the amplitude information and the phase information of optical field in sole spatial light modulation, the experimental system is simple in structure. The experimental results show that the coding method of binary computer-generated holography is an accurate, convenient and efficient way to generate high-quality non-diffracting beams with abundant structures.
Abstract(176) FullText HTML(69) PDF 5885KB(6)
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In order to realize the high-precision surface measurement of large-diameter elliptical optical flat mirrors and improve the image quality of large-aperture telescope systems, the absolute measurement algorithm for flat elliptical mirrors is studied in this paper. Firstly, the orthogonal polynomials fitting of an elliptical optical flat mirror is studied. Then, the absolute testing algorithm is studied theoretically. The orthogonal absolute testing algorithm can effectively separate the face error of the reference mirror from the mirror to be measured, which can realize the high-precision surface reconstruction of the elliptical flat mirror to be measured. To prove the actual testing accuracy of the above method, we carried out an absolute testing simulation and experiment on a 250 mm*300 mm mirror. In the simulation, the possibility that the reference surface error is high was considered. In the experiment, a 250 mm*300 mm elliptical testing area was selected in the Zygo300 mm standard flat surface. The above-mentioned elliptical area was tested by the 150 mm Zygo interferometer, and the surface reconstruction was realized based on the above-mentioned orthogonal absolute testing algorithm. The experimental results show that the surface error separation between the reference mirror and the elliptical mirror can be achieved by using the method described in this paper, and the residual RMS (Root-mean square) value of the absolute testing result is 0.29 nm, which proves the feasibility and accuracy of the method described in this paper. The high-precision surface reconstruction of the elliptical flat mirror can be achieved using the above method.
Abstract(127) FullText HTML(47) PDF 3916KB(14)
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Objective  Aiming at 640×512 long-wavelength infrared cooler detectors, a cooled long-wavelength infrared optical system was designed to track and detect an infrared target.  Method  The optical system adopts the secondary imaging structure pattern to ensure the system has 100% cold-shielding efficiency, and adopts a combination of optical material Ge and ZnS to achieve aberration correction and an achromatic design. By introducing the high-order aspheric surface, the high aberration of the system is well-corrected, thus the system structure is simplified. The optical system is composed of 6 lenses. The focal length is 400 mm, the working bands are 7.7 μm~9.3 μm, the field of view is 1.37°×1.10°, and the F-number is 2. The system adopts the secondary imaging structure to place the system’s exit pupil at the cold screen to ensure the system has 100% cold-shielding efficiency, and introduces the high-order aspheric surface to optimize and balance the aberration of the system.  Result  The design results show that at a spatial frequency of 33 lp/mm, the off-axis field of view MTF>0.24, which approaches the diffraction limit and has high imaging quality.  Conclusion  In the operating temperature range of −35 ℃~+55 ℃, the focusing lens is used to ensure the imaging quality under high and low temperature environments, which can be used for infrared tracking detection over a wide range of temperatures.
Abstract(198) FullText HTML(65) PDF 4599KB(16)
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To address the difficulty in measuring the strain limit of pliable composite film forming tests, a measurement method based on binocular stereo vision combined with digital image correlation is proposed. Firstly, to address the image matching problem in large deformations or cracks in thin films, a weak-correlation step-by-step matching method based on adaptive updating of image matching benchmarks is proposed according to the continuity of adjacent state deformation of series images. Then, according to the differences in the surface strain distribution of the film material is that of the steel parts, a strain field is proposed to fit the limit strain curve of the film material. The software and hardware system of visual measurement is built, and the limit strain curve of a Q235 steel specimen is measured and compared to results from the coordinate grid method. The limit strain accuracy can be improved by 0.02%, which proves the feasibility and accuracy of this method. The pliable composite film specimens prepared by PET, Nylon, Al foil, PP were each measured. The method and system successfully completed the measurement of the forming limit curve of the pliable composite film. The comparative experiments show that the proposed method can quickly and accurately measure the surface strain distribution of pliable composite film during forming. Compared with the coordinate grid method, it has obvious advantages and provides a highly reliable and highly precise method for solving the forming limit strain curve of film materials.
Abstract(181) FullText HTML(62) PDF 4131KB(11)
Abstract:
In order to further improve the calculation accuracy and reduce the calculation time of the inverse algorithm in the Risley-prism structure, a new algorithm is proposed. It combines the forward iterative method is with the equivalent vector model of the Risley-prism to produce an equivalent vector iterative method of calculation. Firstly, the equivalent vector model of the wedge is established according to its deflection. Then, the vector coordinates of the light emitted from the Risley-prism are solved through vector superposition. The equivalent vector model is then substituted into the two-step inverse solution algorithm to calculate the approximate value of the rotation angle of the Risley-prism. Finally, the inverse equivalent vector iteration algorithm is proposed by using forward iteration and gradual approximation, and by calculating the rotation angle of Risley-prism. The experimental results show that the accuracy of the algorithm reaches 10 μm and the calculation time is less than 0.1 ms. The algorithm can effectively improve calculation accuracy, reduce calculation time, and has application prospects in the field of high-precision beams.
Abstract(146) FullText HTML(85) PDF 1147KB(10)
Abstract:
With the development of underwater optical communication, it is very important to study the propagation characteristics of light beams in ocean turbulence. In order to get closer to the actual situation, we build a device which can control both the salinity and the intensity of underwater turbulence to study the propagation characteristics of vortex beams and a Gaussian beam in underwater turbulence. The results show that compared with the underwater turbulence without sea salt, the light spot will be more diffuse and the light intensity will be weaker in the underwater turbulence with sea salt. The scintillation index of the vortex beam with topological charge m=2 in the underwater turbulence with salinity of 4.35‰ is larger than that in the underwater turbulence with salinity of 2.42‰, no matter it is strong turbulence or weak turbulence. When the vortex beam with m=2 propagates to the same distance, the scintillation index increases with the increment of the salinity and the intensity of underwater turbulence. Under different salinity conditions, the radial scintillation index of the vortex beam with m=2 decreases firstly and then increases with the increase of the radial distance. In addition, we set up another experimental device which can transmit a longer distance. The scintillation index of the vortex beam with m=2 is much higher than that of the Gaussian beam in the underwater turbulence within 20 meters, and the scintillation indices of both the vortex beam with m=2 and the Gaussian beam increase with the increase of the propagation distance.
Abstract(149) FullText HTML(84) PDF 3743KB(7)
Abstract:
The single wedge compensation test method, as a testing method for large convex aspheric surface, has good applicability, robustness, and flexibility. However, various errors are coupled with one another during the test process and these errors are difficult to decouple; this affects the accuracy and reliability of the test process. To address this, a method is developed to calibrate the system error of single optical wedge test path using computer generation hologram (CGH). This study first analysed the source of the system error in the optical path of single optical wedge compensation test as well as the feasibility of using CGH for the calibration of an optical wedge compensation test system. In combination with engineering examples, a CGH is designed for optical wedge compensators with a diameter of 150 mm. Based on the analysis results, the calibration accuracy of the CGH is 1.98 nm RMS, and after calibration the test accuracy of single wedge compensation is 3.43 nmRMS, thereby meeting the high-precision test requirements of large convex aspheric mirrors. This shows that CGH can accurately calibrate the pose of single optical wedge compensators and test system errors of optical paths, address the problem of error decoupling in test optical paths, and improve the accuracy and reliability of the single optical wedge compensation method. Meanwhile, using CGH calibration, the system errors of the test optical paths, Tap#2 and Tap#3, are 0.023 and 0.011 λ RMS, respectively.
2021, 14(6): 1305-1316.   doi: 10.37188/CO.2021-0135
[Abstract](167) [FullText HTML](68) [PDF 5353KB](34)
Abstract:
The extinction-to-backscatter ratio is an important optical parameter of aerosols, which is dependent on the type of aerosol. In addition, it is an important source of error in the retrieval of Mie-scattering Lidar. Nowadays, with the rapid development of Lidar in atmospheric aerosol detection, it has become a focus of research. Therefore, it is of great significance to investigate the retrieval methods of the extinction-to-backscatter ratio for aerosol detection and research. According to the choice of instruments and the retrieval principles, this paper summarizes various methods and compares them in terms of optical and microphysical properties. Among them, the light scattering model method, passive optical remote sensing method and Lidar method are closely related and widely used, which provide important support for the detection and research of atmospheric aerosols. This paper mainly introduces these three kinds of relatively mainstream retrieval methods and summarizes the development of related methods. The application, advantages and disadvantages of these methods are analyzed, and their future trends of development are forecasted.
2021, 14(6): 1317-1326.   doi: 10.37188/CO.2021-0067
[Abstract](293) [FullText HTML](82) [PDF 7507KB](46)
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In response to the need for the automated and rapid urine detection, microfluidic technology and biochemical analysis technology are adopted to design and fabricate a disc microfluidic chip used for urine biochemical detection. The chip consisted of microfluidic channels, capillary valve, siphon valve and ferrowax valve which can realize the sequential transportation of the sample and reagent, mixing and detection. COMSOL multiphysics software is used to model the structure of capillary valve and siphon valve and optimize the rotary frequency. Next a fully automatic urine biochemical detection system is generated based on a disc microfluidic chip. The effects of light source fluctuations and background interference on test results are reduced by dual optical path and dual wavelength detection. The detection system is characterized by urinary Retinol Binding Protein (RBP). The results demonstrate the Coefficient of Variation (CV) of the system is 1.3%−2.46%, indicating that the system has good repeatability. The calibration curve shows the linear correlation between urinary RBP concentration and the absorbance (R2=0.995). The four identical unit on the chip could perform a multi-sample or multi-parameter detection in parallel, in which it has a potential to be applied for the rapid detection of urinary protein.
2021, 14(6): 1327-1340.   doi: 10.37188/CO.2021-0075
[Abstract](148) [FullText HTML](69) [PDF 4896KB](15)
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In order to reduce the manufacturing cost of the narrow-bandwidth Metamaterial Absorber (MA) and broaden its application field, a dual-wavelength dielectric narrow-bandwidth MA, composed of Au substrate, SiO2 dielectric layer and Si dielectric asymmetric grating, is designed based on the finite-difference time-domain method using dielectric materials. It is found by simulation that the proposed narrow-bandwidth MA has ultra-high absorption efficiency at λ1 = 1.20852 μm and λ2 = 1.23821 μm, and the FWHM is only 0.735 nm and 0.077 nm, respectively. The main principle that MA achieves the narrow-bandwidth absorption at λ1 is mainly due to the formation of Fabry-Pérot (FP) cavity resonance in the SiO2 layer, while the narrow-bandwidth absorption of MA at λ2 is mainly due to the guided mode resonance effect of the incident light in the asymmetric grating. The theoretical calculations show that the absorption characteristics can be affected more significantly by changing the structural parameters of the MA.
2021, 14(6): 1341-1347.   doi: 10.37188/CO.2021-0013
[Abstract](154) [FullText HTML](66) [PDF 3406KB](11)
Abstract:
In order to improve the luminescent properties of rare earth ions, precious metal nanoparticles were doped into rare earth luminescent materials. Metal plasma resonance can produce local electric field, which acts on the luminescence process of rare earth ions, and can achieve the luminescence enhancement. Ag@SiO2 core-shell nanoparticles can effectively control the distance between metal Ag and rare earth ions, which can not only enhance the plasmonic resonance effect, but also avoid the fluorescence quenching caused by non-radiation energy transfer when they are too close to the emission center. Firstly, the Ag@SiO2 nanoparticles with different concentrations were dropped on the quartz wafers by drop-casting method. Then, the Eu(dbm)3Phen:PMMA: dichloromethane mixed solution was spin-coated to prepare the Eu-PMMA composite film. The morphology characterization and luminescence measurement of the samples showed that the luminescence intensity of the film doped with Ag@SiO2 nanoparticles was enhanced, and the maximum enhancement factor of the measured excitation spectrum was 2.50 times, and the maximum enhancement factor of the emission spectrum was 2.15 times. The results of the fluorescence lifetime measurement of the sample indicated that the luminescence lifetime of the film containing Ag@SiO2 nanoparticles was also prolonged. The doping of Ag@SiO2 nanoparticles in the rare earth luminescent materials shows a good enhancement, and the experimental method is highly operable. It is a promising method to enhance the luminescent intensity of rare earth luminescent materials.
2021, 14(6): 1348-1354.   doi: 10.37188/CO.2021-0107
[Abstract](195) [FullText HTML](91) [PDF 3550KB](11)
Abstract:
The quick fabrication of ring-shaped colloidal photonic crystal was demonstrated on the circle-patterned photoresist substrate by spin-coating, which is promising for practical application. Latex spheres were designed with a hydrophobic core and a hydrophilic shell of poly(styrene-methyl methacrylate-acrylic acid). Scanning Electron Microscopy (SEM) images and reflectance spectra of the as-prepared ring-shaped colloidal photonic crystals were acquired. The influences of spinning speed, latex sphere concentration and different circle-patterned photoresist substrates on the morphology of the ring-shaped colloidal photonic crystal were investigated. The results indicate that the optimal parameters for preparing a ring-shaped colloidal photonic crystal are achieved with a spinning speed of 2000 r/min, a latex sphere concentration of 7.5% and a circle-patterned photoresist structure (diameter: 22.8 µm). The SEM images showed that the latex spheres were almost all deposited at the periphery of the ring and were dispersed with relative order, which was attributed to fast evaporation. This fast self-assembly method for preparing ring-shaped colloidal photonic crystals was achieved by spin-coating and relied on the physical confinement of patterned photoresist substrates and their wettability difference. It will have important applications in optical devices, sensing materials and anti-counterfeiting.
2021, 14(6): 1355-1361.   doi: 10.37188/CO.2021-0054
[Abstract](287) [FullText HTML](108) [PDF 4730KB](28)
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Traditional temperature detection has certain limitations in terms of sensing accuracy and response time. Chip-level photoelectric sensors based on the thermo-optic effect recently aroused widespread interest not only because they can improve measurement sensitivity and speed, but also because they can help reduce system complexity and cost. State-of-art integrated optical temperature sensors mostly measure the optical interference of broadband light sources or tunable light sources in the micro-resonators to provide accurate and fast measurement solutions. However, these solutions based on wide-spectrum detection cannot achieve real-time processing, are costly with complicated signal post-processing, and are difficult to implement in highly integrated systems. To solve the above problems, we show a fast and high-precision temperature measurement method using a silicon-based integrated micro-ring array. The different responses of the cascaded micro-ring array are measured by a single-frequency laser at different temperatures. The results are utilized to model the relationship between the electrical response of the detector array and the real temperature, thereby realizing real-time high-precision temperature measurement. In addition, to enlarge the temperature detection range under a fixed-wavelength light source, a cascaded micro-ring structure is adopted. Based on the proposed structure, a silicon-based integrated temperature sensing system including a light source, a micro-ring array, a detector array, a signal post-processing unit and an output data unit is designed. Depending on the requirement of actual applications, the system can change the temperature measurement range and resolution by separately designing the number of cascaded micro-rings, the center resonance wavelength, and the half-width of the resonance peak while ensuring low system power consumption and cost. Through the optimized design of the micro-ring array, a temperature sensor with a response range covering −20~105°C, accuracy better than 60 mK, and a response time as quick as 20 μs is demonstrated.
2021, 14(6): 1362-1367.   doi: 10.37188/CO.2021-0103
[Abstract](525) [FullText HTML](158) [PDF 3808KB](42)
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Ultra-high quality optical elements are demanded by beamlimes on fourth-generation synchrotron facilities and free-electron laser facilities. A bimorph mirror is effectively used to achieve ultra-high-precision surface profile control and wavefront correction, yet it’s one of the bottlenecks of domestic techniques and must be overcome. In order to accomplish this, a 200 mm long bimorph mirror with 36 elements of piezoelectric actuators was developed. The structure parameters of the bimorph mirror were optimized by numerical simulation, and the bimorph mirror was fabricated by domestic technology. The test results show that the surface profile error and slope error of the bimorph mirror can be reduced to 1.38 nm (rms) and 240 nrad (rms), thus the nanoscale control of the mirror surface profile was realized.
2021, 14(6): 1368-1377.   doi: 10.37188/CO.2021-0051
[Abstract](304) [FullText HTML](61) [PDF 3370KB](41)
Abstract:
In order to overcome the problems where traditional star trackers’ directional accuracy, field of view, volume, weight and other factors are difficult to balance, we studied a highly accurate interferometric star tracker structure based on a diffraction grating. By using the angular spectrum theory, the mathematical models between the incident angle of starlight, the centroid position of spots, and the relative intensity of spots on the detector were established. Secondly, the methods that estimate a relative coarse position of the target star from a centriod of the spots on the detector, and estimate a relative fine position of the target star from the relative intensity of the spots were determined. Therefore, the relative incident angle of star light was obtained by using successive estimates of the coarse and fine positions. Then, we drew a conclusion that the angle resolution for a single star is affected by the grating period, the distance between the two gratings and the electric subdivision of the intensity signal. Finally, a computer simulation was used to confirm the feasibility of this relative fine positioning technique and this combination technique of coarse positioning and fine positioning. The results show that this measure is praticable, and the angle resolution for a single star can reach 0.1 arc-seconds when the grating period is 50 μm, the distance between two gratings is 50 mm and the intensity signal of each period is subdivided by 1024 times. Compared with traditional star trackers, the accuracy is improved significantly.
2021, 14(6): 1378-1386.   doi: 10.37188/CO.2021-0064
[Abstract](280) [FullText HTML](122) [PDF 2582KB](28)
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Ultra-low emission standards of flue gas emitted from stationary sources have been proposed, which creates a new challenge for Continuous Emission Monitoring (CEM). Peak carbon dioxide emissions and carbon neutrality are frequently-mentioned concepts, which means the monitoring of CO2 will eventually be necessary. It is difficult to satisfy the strict limits of ultra-low emission standards with conventional CEM systems. A multi-component trace gas analysis system based on non-dispersive infrared is promoted in this paper to monitor trace gases of continuous emission. A Gas Filter Correlation (GFC) model and Interference Filter Correlation (IFC) model were established, which can describe the relationship of optical length, center wavelength, bandwidth of the filters and gas concentration with measure and reference signals. To confirm the measurement technique of gases, the GFC technique combines with the IFC technique to achieve a double-beam path. With the help of white cells, a small-scale, and the detection limit better than 0.5 mg/m3 can be realized. Zero and span drift are no more than ±2% of the full scale. SO2, NO, NO2, CO and CO2 can be simultenously and continuously monitored to satisfy the requirements of ultra-low and carbon emission monitoring. This technique is helpful for obtaining factual, accurate and comprehensive CEM data.
2021, 14(6): 1387-1394.   doi: 10.37188/CO.2021-0128
[Abstract](125) [FullText HTML](59) [PDF 7236KB](16)
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In order to obtain the 1.6 μm-band mode-locked pulse based on the soliton self-frequency shift effect, an erbium-doped fiber laser with nonlinear polarization rotation is designed, whose pulse is detected by a dual-output structure. At a pump power of 350 mW, the noise-like pulses with the central wavelength of 1560 nm are detected at the two outputs at the same time by properly adjusting the polarization controller. The 3 dB bandwidth is 17.5 nm, and the pulse duration is 968 fs. When the pump power is further increased to 550 mW, and the 1-port noise-like pulse remains fixed, the central wavelength of the 2-port noise-like pulse redshifts to 1614 nm, the 3 dB bandwidth increases to 64.4 nm, and the pulse duration decreases to 302 fs. The maximum output power of the resonant cavity is 11.4 mW. The experiment also analyzes the influence of the length of dispersion shifted fiber on soliton self-frequency shift. The results show that within a certain range, as the length of the dispersion shifted fiber increases, the frequency shift distance of the soliton self-frequency shift decreases. This 1.6-μm band fiber laser has potential applications in the field of optical communications.
2021, 14(6): 1395-1399.   doi: 10.37188/CO.2021-0077
[Abstract](202) [FullText HTML](169) [PDF 3504KB](17)
Abstract:
In order to explore the continuous deep ultraviolet laser output within the wavelength of 200~280 nm, a 5 mm long domestic Pr∶YLF crystal was pumped by the combine of 1.4 W blue laser diode at 444 nm and 1.5 W blue laser diode at 469 nm, and the BBO with a length of 7 mm was used as the frequency doubling crystal. By optimizing the resonator mirror coating and inserting a full wave plate for wavelength competition, it makes the output of weak spectra of Pr∶YLF possible. At last, the continuous deep ultraviolet laser with a maximum power of 8.37 mW and center wavelength of 268.89 nm was achieved.
2021, 14(6): 1400-1409.   doi: 10.37188/CO.2021-0105
[Abstract](188) [FullText HTML](82) [PDF 5215KB](15)
Abstract:
To solve the real-time change of the camera poses caused by the rotation of cameras in free binocular stereo vision, a method for estimating the poses of free binocular cameras based on reprojection error optimization is proposed. The movement paraments of cameras are estimated by decomposing the homography matrix between two adjacent images. Then, the reprojection error of feature points in the overlapping area is calculated, and the objective function is constructed by using the movement parameters as initial values. Finally, the objective function is optimized by the nonlinear optimization algorithm, and the current camera poses are calculated by combining with the optimal movement parameters and the camera poses before rotation. Simulations indicate that the pose estimation error declines with a decrease in reprojection error and the proposed method can converge to a globally optimal solution both rapidly and stably. An experiment of 3D reconstruction of cement models indicates that 3D point clouds of models are generated effectively with the proposed method, the adjacent point clouds are stitched accurately, and the average error of distance between any two points on the stitched point clouds is 1.68%.
2021, 14(6): 1410-1416.   doi: 10.37188/CO.2021-0065
[Abstract](185) [FullText HTML](79) [PDF 4343KB](20)
Abstract:
The dual Mach-Zehnder interferometer system has received extensive attention and applications due to its unique advantages such as simple optical path, high sensitivity and wide frequency response. However, it is very susceptible to external environmental noise and direct cross-correlation calculation method will lead to a large error. This paper proposes a data signal processing scheme based on Hilbert-Huang Transform (HHT) to realize high-precision distributed optical fiber vibration position detection. In this method, the eigenmode function is obtained by the empirical mode decomposition of the two received optical signals. The Hilbert transform and superposition of all eigenmode functions are performed to obtain the Hilbert spectrum, which can be clearly and intuitively extracted. It can accurately calculate the vibration position information by calculating the time delay caused by the vibration signal through cross-correlation. Compared with the traditional direct cross-correlation calculations, this method can effectively identify and extract the characteristic information caused by the vibration signal in the dual M-Z system. Thereby it can effectively reduce the impact of external environmental noise on the system and reduce the positioning error. This paper analyzes the related theory of the proposed method and builds a dual M-Z system for related experimental verification. The experimental results show that, compared with the traditional direct cross-correlation method, this method can effectively reduce the amount of calculation of cross-correlation data. At the same time, it can effectively improve the positioning accuracy of the vibration position. Under 10 MHz sampling rate, the positioning accuracy can reach 10 m. Therefore, the distributed optical fiber sensing technology based on the dual Mach-Zehnder interferometer system proposed in this paper has high application value.
2021, 14(6): 1417-1425.   doi: 10.37188/CO.2021-0078
[Abstract](313) [FullText HTML](132) [PDF 3958KB](41)
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In response to the complex backgrounds of X-ray security images, serious overlap and occlusion phenomena, and the large differences in the placement and shape of dangerous goods, this paper improves the network structure of YOLOv4 for dangerous objects detection by combining atrous convolution with the Atrous Space Pyramid Pooling (ASPP) model to increase receptive field and aggregate multi-scale context information. Then, the K-means clustering method is used to generate an initial candidate frame that is more suitable for dangerous goods detection in X-ray inspection images. Cosine annealing is used to optimize the learning rate in model training to further accelerate model convergence and improve model detection accuracy. The experimental results show that the proposed ASPP-YOLOv4 in this paper can obtain an mAP of 85.23% on the SIXRay dataset. The model can effectively reduce the false detection rate of dangerous goods in X-ray security images and improve the detection ability of small targets.
2021, 14(6): 1426-1434.   doi: 10.37188/CO.2021-0045
[Abstract](210) [FullText HTML](67) [PDF 4844KB](16)
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In the “Taiji mission”, the laser jitter noise caused by satellite jitter is one of the main noise sources that affect the accuracy of laser interferometer. In order to ensure the measurement accuracy, the noise must be suppressed to 10 nrad/\begin{document}$\sqrt{{\rm{Hz}}}$\end{document}@10 mHz. Firstly, an angle sensor composed of a four-quadrant photodetector and a phase meter was used to measure the angle signal, and a Mach-Zehnder interferometer combined with proportional-integral-derivative control technology was used to build a ground-based laser jitter noise suppression system. Secondly, the feedback control capability of the system and the effectiveness of the system to suppress laser jitter noise were analyzed. The experimental results showed that the system could effectively suppress the laser jitter noise, and the laser jitter noise was <4 nrad/\begin{document}$\sqrt{{\rm{Hz}}}$\end{document}@10 mHz. The experiment advanced the study of the “Taiji mission” on the level of laser jitter noise suppression, which laid a physical experimental foundation for laser interferometry.
2021, 14(6): 1435-1450.   doi: 10.37188/CO.2021-0087
[Abstract](168) [FullText HTML](71) [PDF 3990KB](12)
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An initial construction satisfying aberration balance and multi-constraint control is essential for the design of an off-axis multi-reflective optical system with minimal aberration. In this paper, a mathematical model for calculating the initial structure of off-axis multi-reflective is established based on the grouping design method combining spatial ray tracing and aberration correction, and an improved Particle Swarm Optimization (PSO) is proposed to solve the initial structure problem of an off-axis multi-reflective optical system. The PSO of natural selection with shrinkage factor is applied to improve calculation accuracy and design efficiency, so as to obtain the initial structure of the off-axis multi-reflection optical system. In the last part of this paper, taking an Extreme UltraViolet (EUV) lithography projection objective with six-mirror reflective aspheric mirrors as an example, the reliability and effectiveness of this method are verified. A 0.33 numerical aperture EUV lithographic objective with wave-front error better than 1/80λ (λ=13.5 nm) RMS is achieved.
2021, 14(6): 1451-1458.   doi: 10.37188/CO.2020-0190
[Abstract](164) [FullText HTML](61) [PDF 3589KB](14)
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In pure seawater, the transmission window is in the blue-green light band, and blue light has good transmission characteristics. This paper proposes an underwater wireless optical communication system that uses a 470 nm LED array stitching structure, increasing the diverging angle. At the same time, we use Fresnel lens as the optical antenna realizing the wide field of view receiving. At an underwater distance of 20 m, this system could successfully achieve reliable communication at a rate of 5 Mbit/s (data rate) and a BER of 10−6, which lays a foundation for subsequent underwater dynamic laser communication systems.
2021, 14(6): 1459-1467.   doi: 10.37188/CO.2021-0073
[Abstract](232) [FullText HTML](112) [PDF 5629KB](16)
Abstract:
To monitor crop growth more efficiently, various kinds of hyperspectral spectrometers have been designed to detect chlorophyll fluorescence. In this paper, the traditional Offner spectrometer system is improved, and a structure with a higher spectral resolution is obtained. The double-reflection telescope system is selected, and the spectrometer adopts a highly dense linear reflective convex grating to achieve higher spectral resolution. On this basis, an amplifying lens is added to meet the need for a long slit. An Offner structure is obtained with a slit and image plane on the same side of the grating. The initial structure of the telescope system and the spectrometer are optimized by codeV software. The results show that the spectral resolution is 0.3 nm in the range of 670~780 nm, the overall Modulation Transfer Function (MTF) is greater than 0.75 at the cut-off frequency of 17 lp/mm, and the Root Mean Square radius (RMS) of the speckle is less than 15 μm. The proposed system can meet the requirements of highly precise real-time monitoring in crop growth chlorophyll detection.
2021, 14(6): 1468-1475.   doi: 10.37188/CO.2020-0221
[Abstract](214) [FullText HTML](57) [PDF 3927KB](30)
Abstract:
The large field-of-view (FOV) star simulator provides wider star maps but the existing star simulator is limited by the size of the display chip, and the maximum FOV is not more than 30°. In order to increase the FOV of the star simulator, a splicing method is proposed. In order to reduce the cost, the overall weight and complexity of the system, and to achieve the largest splice FOV with the least amount of splicing, we carry out detailed calculation and analysis of the overlapping area of the field of view and propose a simplified splicing model based on plane splicing. Three typical splicing methods are produced including a regular triangle, a regular quadrilateral and a regular hexagon, and the calculation of the FOV utilization is deduced. This paper also provides a coordinate calculation method, determining the center position of each FOV and obtaining an accurate number of the stitching. The final comparison result shows that the regular hexagon splicing method has the outstanding advantages of a higher utilization of the FOV and fewer splicing numbers, which provides a basis for the design of a large FOV star simulator.
2021, 14(6): 1476-1485.   doi: 10.37188/CO.2021-0052
[Abstract](186) [FullText HTML](94) [PDF 4077KB](16)
Abstract:
Ultraviolet radiation of characteristic free radicals and blackbody radiation in combustion flames is essential to the quantitative analysis of flame temperature and fuel composition. An aperture-divided ultraviolet multiband imaging optical system is designed, which consists of an aperture-divided system and an image-combined system. The lens materials are fused silica and calcium fluoride. By placing multiband ultraviolet filters in each divided channel, the combustion flame can be imaged on the detector’s four regions with four ultraviolet bands, including 240~280 nm, 308 nm, 300~360 nm, and 390 nm. The parameters of the system are: a 2.85 F-number, a 10° field-of-view, and a 277.2 mm total length. The entrance pupil diameter of the aperture-divided system is 10 mm, and the single-channel focal length is 43.88 mm. The Modulation Transfer Function (MTF) is close to the diffraction limit. The MTF value of the object surface at the edge of the image-combined system reaches 0.45 at 45 lp/mm. After optimizing the combination of the two parts, the MTF value of the total system surpassed 0.5 at 45 lp/mm in Nyquist frequency. Monte Carlo analysis on the tolerances gives a yield rate of more than 20%. The results show that this system is suitable for research and has practical value.
2021, 14(6): 1486-1494.   doi: 10.37188/CO.2021-0040
[Abstract](145) [FullText HTML](66) [PDF 3977KB](20)
Abstract:
To apply hyperspectral technology to the field of microscopic imaging more conveniently, we designed and built a fully automatic push-broom hyperspectral microscopic imaging system. In this system, an inverted microscope was designed as the main body, a prism-grating component was used for spectrum splitting, a high precision two-dimensional motorized stage was applied for a push-broom. A motor focus module was used to control the focus, and a hyperspectral microscopic image was collected through a highly sensitive sCMOS scientific camera. The system has the advantages of low cost, easy installation and adjustment, real-time focusing and large-field-of-view imaging. The spectral range of the system is from 420 nm to 800 nm to meet the spectrum detection requirements of most biological samples. The spectral resolution was better than 3.5 nm, and the spatial resolution was better than 0.87 μm through the monochromatic collimated light scanning calibration method. Then, the HE-stained breast cancer pathological slices was as the research object. The samples were investigated and compared using passive and active focusing for push-broom imaging. The advantages and disadvantages of the two focusing methods were analyzed and summarized. The results showed that both methods can meet the needs of large-field-of-view imaging, but active focus imaging is faster and clearer, and is more suitable for push-broom hyperspectral microscopy imaging systems. Through the design and research of a fully automatic push-broom hyperspectral microscopy imaging system, real-time focusing in hyperspectral microscopic imaging was realized and 3.25 mm×3.25 mm field of view imaging of biological samples with a 40X objective lens was achieved. This system could be beneficial for promoting the application of hyperspectral technology in the biomedical field.
2021, 14(6): 1495-1503.   doi: 10.37188/CO.2019-0255
[Abstract](583) [FullText HTML](240) [PDF 6836KB](40)
Abstract:
Due to the excessive data transmission of the geostationary orbit array staring spectrometer, the data transmission is difficulty and signal acquisition and processing time is long. According to the characteristic that geostationary orbit platform can stay over the fixed area for a long time, a scheme of large aperture visual and infrared snapshot spectrometer based on compressive sensing was proposed. The physical model of compressive sensing spectral imaging was analyzed, the structure of the optical system was designed, and the relevant parameters were calculated. A coaxial three-mirror afocal optical system was used in objective lens, and dichroic films were used to split the spectrum. After optimization, the optical system was shown with a width of 400 km×400 km, 50 m Ground Sample Distance (GSD) in visible part, 400 m GSD in Middle Wave Infrared (MWIR) part and 625 m GSD in Long Wave Infrared (LWIR) part. The results show that the MTF in the visible part is higher than 0.455 at 78.125 lp/mm, the MTF in mid-wave infrared region is higher than 0.518 at 33.3 lp/mm, and the MTF is higher than 0.498 at 20.8 lp/mm in long-wave infrared region. The spectral resolutions are 20 nm, 50 nm, and 150 nm in the visible part, the mid-wave infrared region, and the long-wave infrared region, respectively. The second-order spectrum of the visual part 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.
2021, 14(5): 1039-1055.   doi: 10.37188/CO.2021-0003
Abstract(1066) FullText HTML(278) PDF 10280KB(325)
Abstract:
Two-dimensional (2D) materials provide new development opportunities for silicon-based integrated optoelectronic devices due to their unique structure and excellent electronic and optoelectronic properties. In recent years, 2D material-based photodetectors for hybrid-integrated silicon photonics have been widely studied. Based on the basic characteristics of several 2D materials and the photodetection mechanisms, this paper reviews the research progress of silicon photonic integrated photodetectors based on 2D materials and summarizes existing device structure and performance. Finally, prospects for strategies to obtain high-performance silicon photonic integrated 2D material photodetectors and their commercial applicability are presented with considerations for large-scale 2D material integrations, device structure, and metal-semiconductor interface optimizations, as well as emerging 2D materials.
2021, 14(5): 1056-1068.   doi: 10.37188/CO.2021-0071
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Optical Frequency Comb (OFC) possesses unique time(frequency) domain characteristics such as narrow pulse width, high frequency precision, stable frequency comb teeth and well-defined optical coherence, etc. Therefore, it has become a hot research topic in various fields including ultra-fast laser technology and metrology science in recent years. Meanwhile, OFC has also been developed into an important scientific research instrument. Recently, a novel light source based on the coherent synthesis of OFCs has been developed, which can realize the periodical, high-speed (up to radio frequency) and stable modulation of the polarization or the orbital angular momentum of light. In this review, we try to introduce recent developments on the fundamental principles, experimental techniques and characterization methods of the novel light source based on the coherent synthesis of OFCs, starting from the basic concepts of OFC and mainly covering two aspects: polarization modulation and orbital angular momentum modulation respectively. We also try to provide some perspectives on the applications of OFC based on the coherent synthesis techniques in the fields of solid-state spectroscopy, optical manipulation and the interaction between light and matter, etc.
2021, 14(5): 1069-1088.   doi: 10.37188/CO.2021-0044
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Because of the large size and immobility working modes, traditional spectral imaging systems struggle to meet increasingly complex practical needs. Tunable micro-nano filtering structures show unique advantages for their lighter weight and greater flexibility, so they are promising candidates for achieving adaptive and intelligent operation in the future. This article summarizes a variety of tunable filtering methodologies and their operational principles both in domestic and foreign research within the last several years. It illustrates static tunable methods such as utilizing liquid crystal and phase-change materials, some dynamic tunable filtering structures such as Fabry-Pérot cavity, micro-nano tunable grating as well as some driving approaches like mechanical stretching, electrostatic driving, optical driving, etc. Meanwhile, this article also introduces some frontier researches based on microfluidic chips and graphene. In the end, it discusses the barriers, challenges and future trends of development for tunable micro-nano filtering structures.
2021, 14(5): 1089-1103.   doi: 10.37188/CO.2021-0022
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The requirements of modern optical engineering in fields such as deep ultraviolet lithography, extreme ultraviolet lithography and advanced light sources drive the continuous development of advanced optical manufacturing technology. Modern optical engineering requires the surface roughness of ultra-smooth optical components to reach the atomic level and the surface shape profile error in the full spatial frequency to reach RMS(Root Mean Square) sub-nanometer or even a few dozen picometers. This drives the manufacturing requirements of ultra-smooth optical components to approach the processing limits. At present, there are still technical challenges to achieve the ultra-smooth polishing technology and equipment required for the above ultra-high precision needs. Atomic level ultra-smooth polishing of complex surfaces such as cylinders, ellipsoids and toroids is still a primary direction of research at both domestically and abroad. Elastic emission machining is an atomic-level ultra-smooth processing method with stable removal functionality and ultra-low subsurface defect creation, which can be used for manufacturing optical components with the above-mentioned accuracy requirements. We summarize the research progress of elastic emission machining and equipment at both domestically and abroad, the principles of elastic emission machining which contains fluid characteristics, the movement characteristics of polishing particles and chemical characteristics, the equipment of elastic emission machining, and the factors affecting the improvement of surface roughness and material removal rate of elastic emission machining. Then we analyze the problems faced by elastic emission machining and equipment and look forward to their prospects. It is expected that this paper will provide a reference for the further development and application of elastic emission machining.
2021, 14(5): 1104-1119.   doi: 10.37188/CO.2021-0033
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As the technology node of large-scale integrated circuits continues to shrink, the focus control of the lithographic tools becomes particularly difficult. In order to ensure the exposure quality of wafers, it is necessary to quickly and accurately adjust the wafer in the Depth of Focus (DOF) to a degree as small as few dozen of nanometers. For this reason, people need to carefully analyze the various factors that cause defocusing or process window changes in the lithographic process, make a reasonable focus control budget, and control the various error factors within a certain range. This paper focuses on Extreme Ultraviolet (EUV) lithography, reviews the factors that affect focus control in the optical path of an advanced EUV lithographic tool and summarizes their principles, simulation and experimental results. It can provide a reference when conducting advanced lithography focus control budget research.
2021, 14(5): 1120-1132.   doi: 10.37188/CO.2021-0125
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Tunable fiber light sources with wavelength near 1 μm are widely used in optical fiber sensing, laser cooling, photochemical, spectroscopy and medical fields. They have thus become an area of focus in fiber light source research in recent years. The development history of fiber light sources with wavelength tuning ability is firstly summarized systematically. Then, their problems and possible solutions are analyzed. Finally, the future developments of tunable fiber light sources near 1 μm are prospected.
2021, 14(5): 1133-1145.   doi: 10.37188/CO.2020-0216
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Chaotic lasers are widely used in secure communication, lidar, optical detection and other applications due to their noise-like randomness, excellent anti-interference and other advantages. Moreover, as semiconductor lasers have small size, stable structure and other advantages, it has become one of the main lasers to produce optical chaos. However, the chaotic laser output from conventional optical feedback semiconductor lasers has the problems of narrow signal bandwidth and delay characteristics, which seriously affect their applications. With consideration for these problems, a comprehensive introduction to reduce the delay characteristics and optimize the chaotic laser bandwidth are reviewed based on recent literatures. This paper also summarizes the research progresses of chaotic secret communication, which is very important in the synchronization of chaotic lasers. The chaotic output of semiconductor lasers and the applications of chaotic lasers are also summarized, and then their development and potential future applications are discussed.
2021, 14(5): 1146-1161.   doi: 10.37188/CO.2021-0032
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Augmented reality (AR) display technology has developed rapidly in recent years, and has become a research hotspot and development focus of the global information technology industry. It has the potential to revolutionize the ways we perceive and interact with various digital information. Recent advances in micro-displays and optical technologies offer new development directions to further advance AR display technology. This review analyzes the optical requirements of human visual systems for AR head-mounted displays and compares them with current specifications of AR head-mounted displays to demonstrate their current levels of development and main challenge. The basic principles and parameters of various micro-displays and optical combiners in AR head-mounted displays are introduced to explain their advantages and practicability, and their development trends are summarized.
2021, 14(3): 447-457.   doi: 10.37188/CO.2020-0199
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Intelligent manufacturing has become more precise, miniaturized and integrated. Representative integrated circuit technology and its derived miniature sensors such as Micro-Electro-Mechanical System (MEMS) have become widely used. Therefore, it is important for intelligent manufacturing development to accurately obtain the surface morphology information of micro-devices and implement rapid detection of device surface defects. Fringe Projection Profilometry (FPP) based on structural light projection has the advantages of being non-contact, highly precise, highly efficient and having full-field measurement, which plays an important role in the field of precision measurement. Microscopic Fringe Projection Profilometry (MFPP) has been developed rapidly during recent decades. In recent years, MFPP has made great progress in many aspects, including its optical system structures, corresponding system calibration methods, phase extraction algorithms, and 3D coordinate reconstruction methods. In this paper, the structure and principle of a three-dimensional measurement system of microscopic fringe projection are reviewed, and the calibration problem of a small field-of-view system that is different from the traditional projection model is analyzed. After that, the development and improvement process of the micro-projection system structure is introduced, and the reflection in the measurment caused by the system structure and metal material is analyzed. On this basis, the prospects of the development of microscopic fringe projection of 3D measurement system are discussed.
2021, 14(3): 458-469.   doi: 10.37188/CO.2020-0180
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Mid-infrared lasers with emission spectrums located in the 3~5 μm atmospheric window have a wide range of possible applications in medical treatment, industrial processing, atmospheric remote sensing, space communication, infrared countermeasures and other fields. Transition Metal (TM) doped Ⅱ~Ⅵ group sulfide crystals can be used as the gain medium to achieve mid-infrared laser output. Among them, Fe2 +:ZnSe lasers are advantageous for their high conversion efficiency, their wide tunable range in the mid-infrared band and their compact structure. They are one of the most effective ways of achieving a short pulse with high power and high energy in the mid-infrared band. With the development of material technology in recent years, Fe2 +:ZnSe lasers have begun developing rapidly and have become a heavily researched topic. This paper reviews the development of a TM2+:Ⅱ~Ⅵ laser represented by a Fe2 +:ZnSe laser. The preparation methods of a Fe2 +:ZnSe gain medium are introduced and analyzed. The pump sources and factors affecting the performance of Fe2 +:ZnSe lasers are discussed. The output characteristics of the Fe2 +:ZnSe laser are reviewed. The latest development of Fe2 +:ZnSe lasers in room temperature and ultrashort pulse directions is summarized and prospected. The possible future development direction of Fe2 +:ZnSe lasers is discussed.
2021, 14(3): 470-486.   doi: 10.37188/CO.2020-0093
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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.
2021, 14(3): 487-502.   doi: 10.37188/CO.2020-0134
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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 analyzed.
2021, 14(3): 503-515.   doi: 10.37188/CO.2020-0039
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Abstract:
Polarization modulation technology based on 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 LiNiO3 (LN) materials, it is difficult for traditional electro-optic modulation technology to further improve 3D imaging performance. As the preparation technology of perovskite-structured electro-optical materials becomes more mature, electro-optic modulation technology based on new materials will become an excellent means to create a breakthrough in the detection accuracy of laser 3D imaging. PMNT, PLZT and KTaxNb1-xO3 (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 modulation bandwidth for PMNT, poor transmission performance for PLZT, and low practical application bandwidth for KTN. Future research will focus on the practicality of this modulation technology. The electro-optic modulation performance can be improved by doping and the signal-to-noise ratio of the system can be optimized by establishing performance characterization models.
2021, 14(3): 516-527.   doi: 10.37188/CO.2020-0051
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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 compare the performance 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 research and analysis the improved design of receivers in optical OFDM systems. The challenges and upcoming research of OFDM systems in VLC are summarized. The research in this paper can provide a research reference and propose more efficient unipolar modulation schemes to further improve the spectral efficiency and reliability of optical OFDM systems.
2021, 14(2): 227-244.   doi: 10.37188/CO.2020-0126
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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, we introduce 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 the prospects for the future development of freeform surface adaptive interferometers are proposed.
2021, 14(2): 245-263.   doi: 10.37188/CO.2020-0121
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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.
2021, 14(2): 264-274.   doi: 10.37188/CO.2020-0193
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Near-infrared continuous-wave fiber lasers with wavelengths of 0.9~1.0 μm have important application prospects in the fields of high-power blue and ultraviolet laser generation, high-power single-mode pump sources, biomedicine and lidars. They have thus become a heavily researched topic in recent years. At present, their gain mechanisms mainly include a rare earth ion gain or a nonlinear effect gain. In this paper, the research progress of 0.9~1.0 μm fiber lasers based on these two kinds of gain mechanisms are reviewed in detail, and the technical bottlenecks and solutions of these lasers are analyzed. Furthermore, the potential directions for the future of their research are proposed.
2021, 14(2): 275-288.   doi: 10.37188/CO.2020-0098
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The Time-delay Interferometry (TDI) technique is of important value for China’s gravitational wave detection program and other space-based laser interferometry missions. 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, TDI technique is used to remove laser noise and displacement noise of optical platform 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 GHz clock signals are added on inter-satellite laser links by phase modulation. 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 5.8×104, respectively.
2020, 13(6): 1171-1181.   doi: 10.37188/CO.2020-0033
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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
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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.

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