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PDF 743KBLong-period fiber gratings have the advantages of small size, corrosion resistance, anti-electromagnetic interference, and high sensitivity, making them widely used in biomedicine, the power industry, and aerospace. This paper proposes a long-period fiber grating sensor based on periodic microchannels. First, a series of linear structures were etched in the cladding of a single-mode fiber by femtosecond laser micromachining. Then, the laser-modified region was selectively eroded by selective chemical etching to obtain the periodic microchannel structure. Finally, the channels were filled with polydimethylsiloxane (PDMS) to improve the spectral quality. The experimental results show that the sensor has good sensitivity in the measurement of various parameters such as temperature, stress, refractive index, and bending: it has a temperature sensitivity of −55.19 pm/°C, a strain sensitivity of −3.19 pm/με, a maximum refractive index sensitivity of 540.28 nm/RIU, and a bending sensitivity of 2.65 dB/m−1. All of the measurement parameters show good linear responses. The sensor has strong application prospects in the field of precision measurement and sensing.
Brain glioma is a typical and common brain tumor with low cure rate and high recurrence rate. Precise identification of tumor boundaries is an important prerequisite for reducing recurrence and improving prognosis. It has an important clinic significance for glioma to develop a rapid, high-sensitive and label-free diagnostic method. Raman spectroscopy can reflect the chemical and structural information of substance at the molecular level due to its fingerprint characteristics, which has already shown great prospects for the location and identification of glioma. Firstly, we introduce the different types of Raman spectroscopy technologies in this paper. Secondly, the research status of glioma based on Raman spectroscopy is reviewed. Finally, the future development of glioma through Raman spectroscopy is prospected.
To study the visible light polarization reflection characteristics of typical terrain target materials, an improved Blinn type shadow masking function is introduced according to traditional "V" surface structural defects. Additionally, the effects of mirror reflection, diffuse reflection, and volume scattering are comprehensively considered. A six-parameter two-dimensional reflection distribution function model for typical terrain target materials is established. Testing of polarization characteristics is conducted on target samples with different materials (polypropylene plastic sheet, 99 alumina ceramic sheet, iron sheet, green painted aluminum sheet) in the visible light 600 nm wavelength band. A genetic algorithm for parameter inversion is used. The experimental and simulation results show that compared with the traditional "V" shielding model, the polypropylene plastic plate model has the highest accuracy improvement and a 70.61% increase in RMSE percentage in the impact of observation angles on the polarization characteristics of the target material surface at an incidence angle of 50°, relative azimuth angle of 180°, and 0° to 60°. Compared with the two reference models, the DoLP model shows a significant improvement in accuracy at an incidence angle of 50°, observation angle of 50°, and relative azimuth angle of 90° to 270°. The model accuracy has improved by at least 24.73 percentage points. The minimum root mean square error of linear polarization is only 1.29%. For the material in this article, the polarization characteristics depend on the value of its complex refractive index. When the incident angle is determined, the observation angle is between 0° and 60°, and the relative azimuth angle is between 0° and 360°. The larger the
In the digital grating displacement measurement technique, the CMOS pixel array of the camera is regarded as a ‘digitized’ grating. The micron-scale grating images can realize nanoscale displacement measurement by constructing the period difference between optical grating and digital grating. Combined with the detection light path of oblique incidence, it can be applied to the focusing and leveling sensor of lithography machine to measure the wafer surface height accurately. In the actual measurement, the unexpected patterns on the wafer surface will interfere with the reflection imaging of the optical grating, then affect the results of image processing. In this paper, a process adaptability method for digital grating displacement measurement is proposed, which reconstructs the light intensity and recovers the light intensity curve from the CMOS image when interference patterns exist. It shows good stability when the large area pattern appears on the wafer substrate, which can adapt to multiple surface defects such as scratches, particles, stains and grooves. The experimental results show that the mean square error of the light intensity curve is greatly reduced and the Z-direction error correction by the method is within ±33 nm(±3
The study of the radial structure and optical radiation characteristics of the cloud-ground lightning channel can provide a reference for the revealing the microphysical mechanism of the formation and development of the cloud-ground lightning channel, and provide scientific guidance for the lightning protection. The research team carried out field observation experiments in the Qinghai Plateau region using a slit-less high-speed spectrograph. The clearly visible channel core was recorded in a cloud-ground lightning, and a weak luminescent region was found between the outer edge of the channel core and the external luminescent channel. Based on the spectral observation, the optical radiation characteristics of the first return stroke and the third subsequent return stroke are compared and analyzed. The corona sheath model of the lightning channel is verified experimentally, the location of the connection point is determined, and the estimated striking distance of the two return strokes is 57 m and 53 m respectively, and the strongest point of the return discharge is confirmed at the connection point. It can be inferred that in the initial stage of the return stroke, the cloud ground lightning return stroke channel consists of the channel core , the weak luminescence region and the outer corona sheath from the inside to the outside, that is, the charge distribution along the radial direction of the lightning channel is uneven. The light emission characteristics of lightning channel are closely related to the intensity and duration of discharge.
Fourier transform spectroscopy (FTS) is an effective method for gas composition analysis and accurate measurement of concentration. However, in the process of analysis, the saturated absorption and weak absorption of the measured gas make the transmittance of some bands deviate from the stable range, which leads to the decrease of spectral signal-to-noise ratio and the nonlinear response of the instrument, and reduces the accuracy of concentration inversion.
In this paper, an adaptive multi-band joint concentration inversion algorithm is proposed, which combines the transmittance stable range and the spectral width threshold to adaptively select the effective band of the measured gas. The nonlinear least squares fitting method is used to invert the concentration of each effective band and the residual analysis is carried out to obtain the concentration inversion results and their weights of each effective band. The accurate quantitative analysis of the measured gas is realized by weighted average.
: The algorithm verification experiment is designed and carried out; the results show that the stability coefficient of the adaptive multi-band joint concentration inversion algorithm is 0.9976. Compared with the traditional single-band and multi-band concentration inversion algorithms, the root mean square error of the inversion results is reduced by 64.44% and 41.52%, the mean relative error is reduced by 65.97% and 46.72%, and the mean absolute error is reduced by 66.32% and 47.74% respectively,
the inversion accuracy and stability are significantly improved.
In order to solve the problems of low image exposure, low contrast, and difficulty of feature extraction in real-time animal monitoring at night, this paper studies the use of a lightweight self-supervised deep neural network Zero-Denoise and an improved YOLOv8 model for image enhancement and accurate recognition of nocturnal animal targets.
The first stage of rapid enhancement was performed by lightweight PDCE-Net. A new lighting loss function was proposed, and the second stage of re-enhancement was carried out in PRED Net based on the Retinex principle and the maximum entropy theory, using the original image and fast enhancement image corrected by the parameter adjustable Gamma. Then, the YOLOv8 model was improved to recognize the re-enhanced image. Finally, experimental analysis was conducted on the LOL dataset and the self-built animal dataset to verify the improvement of the Zero-Denoise network and YOLOv8 model for nocturnal animal target monitoring.
The experimental results show that the PSNR, SSIM, and MAE indicators of the Zero-Denoise network on the LOL dataset reached 28.53, 0.76, and 26.15, respectively. Combined with the improved YOLOv8, the mAP value of the baseline model on the self-built animal dataset increased by 7.1% compared to YOLOv8.
Zero-Denoise and improved YOLOv8 can achieve good quality images of nocturnal animal targets, which can be helpful in further study of accurate methods of monitoring these targets.
In order to enhance the continuous tunable range of a self-injection-locked laser frequency, a study is conducted on the variation relationship of the injected locking phase of the FP microcavity during the frequency-thermal tuning process.
Building upon traditional frequency thermotuning methods, this study explores the characteristics of frequency and phase parameters of a self-injection locked laser. We proposed an improved algorithm that integrates injection locking phase compensation and DFB chip current compensation during frequency thermotuning. Experimental validation of this algorithm was conducted on a Fabry-Perot (FP) micro-cavity self-injection locked laser. The laser operates at a wavelength of 1550nm with a 3dB linewidth of 785Hz, achieving frequency thermotuning of the FP micro-cavity using a pair of heating resistors.
The enhanced algorithm is implemented within the microcontroller program of the laser's original drive control circuit. No modifications are made to the hardware components of the laser. Ultimately, this implementation achieves a continuous frequency tuning range of 6 GHz.
This work provides a simple, efficient, and stable frequency tuning solution for self-injection-locked lasers, demonstrating high practicality and promising market prospects.
To mitigate reliance on operators during fundus imaging, an automated rapid localization and alignment method for the human pupil was proposed for visible light pupil imaging.
Initially, the pupil alignment device was constructed on the laboratory fundus imaging system using a visible light camera module and a three-axis motorized displacement stage.Subsequently, the effective area of the image was extracted using the Hough gradient method to determine the center of the fundus imaging system. The pupil region was identified through the maximum inter-class variance method and image histogram feature, while the center of the pupil was ascertained via the minimum circle fitting method. Ultimately, the electric displacement stage's movement is regulated through feedback mechanisms, ensuring that the center of the fundus imaging system aligns precisely with the pupil's center.
The experimental results show that the average recognition speed of human pupil is 0.11s, the average recognition accuracy of the pupil center is 98.7%, and the average Euclidean distance of the center deviation is 4.3 pixels.
It can satisfy the system requirements of the real-time and accuracy, and provides an efficient automatic pupil alignment solution for fundus imaging system.
Solar glint is a significant factor influencing sea surface target detection. For land observation platforms, a sea surface glint suppression method based on the reconstruction of common characteristics of linearly polarized images is proposed using the polarization characteristics of glints. The proposed method uses a focal plane polarization camera to obtain four-channel linear polarized images, calculates the scene’s polarization information, and generates a glint suppression image. Based on suppressing scene glint with polarization information combined with the characteristics of linear polarization images, the light intensity components of the glint suppression image are decomposed into common and characteristic components, and new weight factors are given to obtain the reconstructed glint suppression image. The results of field polarization experiments show that the maximum relative decrease in the proportion of saturated pixels in the reconstructed glint suppression image compared to the intensity image was 79.07%, and the maximum relative increase in spatial frequency and contrast were 73.77% and 172.73%, respectively. The method proposed in this paper effectively suppresses the glint noise in the sea scene and performs well in restoring background detail information.
The development of third-generation infrared focal plane detectors allows them to respond simultaneously to two different bands of infrared radiation, and the dual-band image brings great benefits to target detection and identification. In this paper, for aerial detection applications, adopting 320×256 dual-color infrared cooled detector, a large-magnification-ratio cooled infrared dual-band zoom optical system with operating bands of 3.7−4.8 μm in the midwave and 7.7−9.5 μm in the longwave has been designed for infrared detection of targets. The optical system adopts a combination of transmissive and refractive structures to realize an optical four-field-of-view switching wide-range zoom, and in order to meet the 100% cold diaphragm efficiency, a secondary imaging mode is adopted. The four-field focal lengths of the optical system are 32 mm, 200 mm, 800 mm, and 1600 mm, and the zoom ratio is 50×. The experimental results show that the optical system is close to the diffraction limit at a modulation transfer function eigenfrequency of 17 lp/mm in each of the dual-band zoom states. The optical system has the characteristics of dual-band, large zoom ratio, large zoom range, fast switching of multiple fields of view, simple and compact structure, and high-quality imaging, which will be widely used in the security fields such as searching, reconnaissance, and so on.
The anamorphic optical system is a relatively special optical system with bi-planar symmetry, whose structure gives rise to non-rotationally symmetric polarization aberrations. This thesis constructs a foldback anamorphic optical system. It also systematically analyzes the polarization aberration of this system and its effect on the point spread function, with the aim of providing a reference for the design of subsequent anamorphic optical systems.
Simulations of a folded-reversal anamorphic optical system based on a three-dimensional polarized light trace were performed to obtain detailed data on the polarization aberration and to compute the two-way attenuation and phase delay distribution characteristics of individual surfaces, as well as the Jones pupil, the amplitude response matrix, the point spread function, and the polarization crosstalk contrast of the system.
The maximum two-way attenuation is 0.145, and the maximum phase delay is 1.46×10−2 rad, both occurring at the secondary mirror position. The amplitude response function of the optical system with a 2∶1 anamorphic ratio has a 40.6% difference between the polarization crosstalk term in the long and short focal end directions, and the polarization crosstalk is limited by an order of magnitude of 10-6 for this anamorphic optical system contrast.
Polarization aberration in high-precision anamorphic optical systems is not negligible. The effects of polarization aberration can be reduced by film layer design and folded-back structure. The conclusions of this study can serve as a reference for designing anamorphic optical systems in deep space exploration and coherent communication systems.
In order to realize the industrial application of high-current pulsed electron beam on material surface modification, real-time tiny perturbation monitoring of the electron beam action process is needed. The electric field strength is one of the key parameters to reflect the characteristics of electron beam. The laser induced fluorescence-dip spectroscopy method based on Stark effect can realize the tiny perturbation measurement of electric field. Therefore, study the influence of laser power density on the electric field has important theoretical and application value for the parameter setting and result interpretation of similar electric field measurement methods.
By the theoretical analysis and calculation, the relationship model between excitation laser power density and the parameters of the test environment in the tiny perturbation state of electric field measurement is obtained; Then, based on the above relationship model and theoretical calculation, the influence of excitation laser power density on electric field measurement is verified experimentally.
The experimental results show that under the conditions that the tracer gas xenon pressure is 1.0×10-4 mbar and the electric field strength is 2 kV/cm or below, the excitation laser power density of tiny perturbations on the electric field measurement is 5 MW/cm2, which is basically consistent with the theoretical calculation value.
The research results provides the quantitative analysis method of the influence of laser power density on electric field in the laser induced fluorescence-dip spectroscopy method, and can be applied in the same kind of electric field measurement methods, providing the way for the setting of laser power density and experimental parameters, support the development of electric field measurement experiments, and effectively improve the accuracy of electric field measurement.
Phase delay mirrors were designed and prepared to regulate femtosecond laser systems’ group-delay dispersion (GDD). This paper systematically investigates the principle of compensating group-delay dispersion by phase-delay mirrors. Nb2O5 and SiO2 were used as the materials with high and low refractive indices. The group-delay dispersion curves were smoothed out by pairing the phase-delay mirrors with their complementary mirrors. The phase-delayed mirrors with phase modulation data of −800 GDD were prepared, and the reflectivity reached more than 99% in the range of 900 nm−1100 nm. The bandwidth adjustment problem of femtosecond laser systems is solved to meet the requirements of femtosecond lasers
Visual detection of sonar image is one of the important technologies in the field of resource exploration in complex waters and underwater foreign object target detection. Aiming at the problem of weak features and background information interference of small targets in sonar images, this paper proposes a weak feature confocal channel modulation algorithm for underwater sonar target detection. Firstly, in order to improve the model's ability to capture and characterize the information of weak targets, we design a weak target-specific activation strategy and introduce an a priori frame scale calibration mechanism to match the underlying semantic feature detection branch to improve the accuracy of small target detection; secondly, we apply the global information aggregation module to deeply excavate the global features of weak targets to avoid the redundant information from covering the small target's weak key features; lastly, in order to solve the problem of the traditional space pyramid Finally, in order to solve the problem of traditional spatial pyramid pooling which is easy to ignore the channel information, the confocal channel regulation pooling module is proposed to retain the effective channel domain small target information and overcome the interference of complex background information. Experiments show that the model in this paper achieves an average detection accuracy of 83.3% on nine types of weak targets in the underwater sonar dataset, which is 5.5% higher than the benchmark, among which the detection accuracy of iron bucket, human body model and cube is significantly improved by 24%, 8.6% and 7.3%, respectively, which effectively improves the problem of leakage and misdetection of weak targets in the underwater complex environment.
The rich blood flow information contained in the pulse is becoming a hot spot in research to detect the pulse and derive the health status of the human cardiovascular system. In this study, PbS quantum dots with a size of 3 nm were synthesized using the hot injection method, and a PbS quantum dot photodetector was constructed on the surface of gold forked fingers electrode through spin coating. Based on the prepared PbS quantum dot photodetector, a data visualization pulse detection system was developed. Using the optoelectronic capacitance pulse wave recording method, we measured the same tester under different exercise states and different testers under the same exercise state, and displayed the measured data on the electronic display screen through circuit processing. The results show that under the illumination of 15.2 μW cm−2 light intensity, its responsivity (R) and light detection rate (D*) are 0.33 A/W and 1.33×1012 Jones under −3 V bias voltage, respectively. When used in the pulse measurement circuit, the system can effectively receive and measure the human pulse signal, proving that the pulse detection system based on the PbS quantum dot photodetector meets the application requirements in terms of sensitivity, stability, and reliability.
Aiming at the low accuracy of existing non-contact blood oxygen saturation measurement methods in dynamic head scenes, a denoising method based on improved adaptive noise complete set empirical mode decomposition and wavelet threshold is proposed to extract pulse wave signals with high signal-to-noise ratio. Firstly, in order to solve the problem of false components and mode aliasing in the early stage of decomposition and reconstruction, white Gaussian noise is added to the decomposition process to make it become an improved ICEEMDAN (ICEEMDAN), so as to reduce the residual noise in the modal components. Then, ICEEMDAN was used for mode decomposition of pulse wave signals of red and blue channels, and db8 wavelet basis function was used for 3-stage decomposition and reconstruction of components conforming to the spectrum range of blood oxygen, and the reconstructed signals were used for subsequent calculation of blood oxygen value. Finally, the experimental comparison and analysis of the blood oxygen saturation results measured in different dynamic head scenes show that the average error of blood oxygen saturation obtained in different head scenes is 0.73%, which is 1.93% lower than the average error of other algorithms. The denoising method proposed in this paper has good stability in different head scenes and can meet the needs of daily blood oxygen saturation measurement.
The teaching scan is cumbersome and has poor versatility when performing scan reconstruction. The current focus of viewpoint planning is still to automatically obtain the minimum set of viewpoints covering the model. To realize automated 3D scanning and reconstruction of parts of different complexity levels, this paper studies issues such as viewpoint redundancy, viewpoint occlusion, and binocular reconstruction constraints that may occur during viewpoint planning. First, given the problem that it is difficult to completely scan the model with existing viewpoint planning, Lloyd's algorithm was improved by analyzing the characteristics of surface structured light scanning and proposed using the energy function of Euclidean distance and normal vector deviation to perform Voronoi partitioning of the model to generate Initial scanning viewpoint. Then, to address the viewpoint redundancy problem, an iterative algorithm for splitting the initial scanning viewpoints is proposed. Finally, given the problem that the generated viewpoints are prone to occlusion, a line-of-sight de-occlusion strategy is proposed, and to improve the model coverage, a method of using panning viewpoints is proposed. The experimental results show that: under the optimal number of viewpoints, the coverage rate of automobile castings and transmission housing reaches more than 94%, the coverage rate of simple curved automobile sheet metal reaches more than 99.5%, and the automatic steering knuckle of the automobile is realized. Planning scanning meets the coverage and efficiency requirements of automatic viewpoint planning and the adaptability requirements for parts of different complexity.
Triangular mesh model registration is an important part of industrial automation detection software. The registration accuracy has an important influence on the shape and position tolerance of mechanical parts. Aiming at the problems of low accuracy and poor robustness of automatic registration of triangular mesh models, this paper proposes a segmentation method for enhanced features in automatic registration of triangular mesh models for mechanical parts. Firstly, the K value of the feature segmentation of the triangular mesh model is determined, and the seed points are determined by the Laplacian matrix for iterative initialization. Secondly, this paper uses the appropriate region shape agent and cost function to accelerate the process, and performs multi-source iterative clustering to obtain the feature segmentation results. Finally, based on the feature segmentation results of the triangular mesh model, the coarse registration based on the singular value decomposition method is performed, and the fine registration is performed according to the EM-ICP. Compared with the traditional feature descriptor coarse registration and ICP fine registration method, the experimental results show that the registration error of the proposed method is reduced by 25.2 %, and the automatic registration time is shortened by 62.6 %, which effectively improves the accuracy and efficiency of the automatic registration of the triangular mesh model.
In the article, we report a 4.7 μm mid wave infrared quantum cascade laser based on double active regions, with a ridge width of 9.5 μm, It can achieve continuous single transverse mode operation at room temperature. By inserting 0.8 μm InP, the original single active region is transformed into a double active region structure, it can significantly reduce the peak temperature of the device's active region and suppress the generation of higher-order transverse modes. At a temperature of 288 K, the device with a double active region structure with a cavity length of 5 mm has a threshold current density of 1.14 kA/cm2, the continuous output power of 0.706 W, the fast axis divergence angle of 27.3°, and the slow axis divergence angle of 18.1°. Compared with conventional devices with a single active region structure, the devices with a double active region structure have no degradation in their maximum optical output power, and the beam quality in the slow axis direction of the device has been significantly improved. This work provides another solution for improving the slow axis beam quality of high-power medium wave quantum cascade lasers.
Monocentric multiscale systems offer the advantages of miniaturization and large field of view. In order to further realize the miniaturization and lightweight of the large-field-of-view system, this paper adopts the Galileo-type monocentric multiscale system form and designs a monocentric multiscale system operating in the visible spectrum.The modulation transfer function curve of the system is greater than 0.3 at a frequency of 208 lp/mm, and the root-mean-square radius of the full-field diffuse spot is smaller than the detector pixel size of 2.4
Narrow linewidth lasers are the basic components of spectroscopy and precision metrology and other experiments. Because semiconductor laser is very sensitive to external optical feedback, the phase noise of semiconductor laser can be suppressed by using the high bandwidth of optical feedback, and then the linewidth can be narrowed. So we use fiber Bragg grating as feedback element and build a long external cavity feedback loop. In order to reduce the influence of external environment temperature fluctuation and air flow disturbance, we control the temperature of the fiber of the feedback optical path. Then the maximum temperature fluctuation within 1 hour is reduced from 0.039 °C to 0.003 °C, and the variance of temperature fluctuation is reduced by two orders of magnitude. In addition, we also test the effect of feedback bandwidth on laser linewidth. Although the bandwidth of the fiber Bragg grating used in our experiment is much larger than the free-running laser linewidth, we still observe that the laser linewidth is narrowed, and the smaller the bandwidth of the fiber Bragg grating, the narrower the laser linewidth. For this phenomenon, we believe that there should be a negative feedback mechanism in the feedback loop, which can stabilize the laser linewidth to a certain slope of the feedback spectrum, so the narrower the feedback bandwidth of the fiber grating, the larger the slope of the feedback spectrum, the more sensitive the feedback. In addition, by changing the feedback power of FBG in the range of 0~1 mW, we observed that at the reflected power of 0.8 mW, the optical feedback narrowed the laser linewidth from the free-running 100.5 kHz to the narrowest 11.5 kHz, and at the reflected power of 1 mW, phase noise in the range of 0.2 kHz to 2 MHz is suppressed by about 22 dB.
In order to improve the detection accuracy of Doppler asymmetric spatial heterodyne (DASH) interferometer in harsh temperatures, an Opto-mechanical-thermal integration analysis was carried out. Firstly, the correlation between the interference phase and temperature is established according to the working principle and the phase algorithm of the interferometer. Secondly, the optical mechanical thermal analysis model and thermal deformation data acquisition model are designed. The deformation data of the interference module and the imaging optical system at different temperatures are given by temperature load simulation analysis, and the phase error caused by thermal deformation is obtained by fitting. Finally, based on the wind speed error caused by thermal deformation of each component, a reasonable temperature control scheme is proposed. The results show that the interference module occupies the main cause, the temperature must be controlled within 20±0.05 °C, and the temperature control should be carried out for the temperature sensitive parts, and the wind speed error caused by the part is 3.8 m/s. The thermal drift of the magnification of the imaging optical system and the thermal drift of the relative position of the imaging optical system and the detector should occupy the secondary cause, which should be controlled within 20±2 °C, and the wind speed error caused by the part is 3.05 m/s. In summary, the wind measurement error caused by interference module, imaging optical system, imaging optical system and relative position of detector can be controlled within 6.85 m/s. The analysis scheme and temperature control measures presented in this paper can provide theoretical basis for DASH interferometer engineering applications.
为了提高压电定位系统（Piezo-positioning system）的控制性能，对迟滞特性产生的影响及其补偿控制方法进行了研究。利用Hammerstein模型表征压电陶瓷定位器的动态迟滞非线性特性，分别以Prandtl-Ishlinskii（P-I）模型和Hankel矩阵系统辨识法求得的模型表示Hammerstein模型的静态非线性部分和动态线性部分。此模型对于200 Hz以内的典型输入频率具有较好的泛化能力。提出了基于P-I逆模型与积分增广的滑模逆补偿跟踪控制策略，实验结果表明，相较于PID逆补偿控制和无逆补偿的滑模控制，滑模逆补偿控制具有更加理想的阶跃响应，无超调且调节时间仅为6.2 ms，在频域内系统闭环跟踪带宽达到119.9 Hz，且扰动抑制带宽达到86.2 Hz。所提控制策略实现了迟滞非线性的有效补偿，提高了压电定位系统的跟踪精度与抗扰性能。
Laser beam quality is one of the key indicators considered when measuring the performance of laser applications. To meet the application requirements of long-distance optoelectronic countermeasures, this paper researches the design of unstable resonators and beam quality improvement techniques for non-chain DF lasers. Three sets of positive branch confocal unstable resonators with different magnifications are designed. An experimental setup for an unstable inner cavity resonator is constructed with two convex mirror structures: transverse support and longitudinal support. The transverse support structure is equipped with a circulating water-cooling channel. Using 86.5% surrounding energy to define laser beam diameter, the laser beam quality is evaluated with beam quality factor β, and the energy and beam divergence for two support types of convex mirrors are compared. Research has found that, under the same conditions, the laser energy of unstable resonators with longitudinal support is 6% higher than that of the transverse support structure. Still, the far-field divergence angle is 9% larger than that of the transverse support structure. Although the water-cooled transverse support structure has energy shielding, its high thermal stability significantly improves the quality of the laser beam. A beam divergence of θ0.865 = 0.63 mrad with beam quality factor β=1.83 is obtained at M=2.25 with a transverse support unstable resonator. The laser energy under this condition is 2.34 J, the laser pulse width is 88.2 ns, and the peak power reaches 26.5 MW.
Shared secret-key extraction from random channel characteristics is an effective approach to ensuring the physical layer security of atmospheric optical channels. The secret-key generation rate and disagreement rate are two issues that attract a lot of attention. Using the random characteristics of atmospheric turbulent optical channels as a shared source of randomness, a secret-key extraction scheme for multiple-input multiple-output (MIMO) atmospheric optical channels is proposed. The alternative singular value decomposition is used to decompose the channel matrix; the correlation between the two channel characteristic sequences obtained by the two legitimate parties is enhanced by carrying out a simple moving average; a channel quantization alternating scheme with a single threshold is used to quantize the resultant channel characteristic sequences. The two legitimate parties generate random controlling sequences for coding mapping based on differential diversity values, which are used in performing coding mapping of the quantized bits of the channel characteristic sequences generated by the channel quantization alternating scheme with a single threshold. The experimental results show that our scheme’s initial key disagreement rate can reach 5.2×10−4 at a signal-to-noise ratio of 30 dB, and that the generated random bit sequences have passed the National Institute of Standards and Technology (NIST) randomness test. This paper’s results are useful in the implementation of secret-key extraction from atmospheric MIMO optical channels.
There is nonradiative recombination in waveguide region owing carrier leakage, which in turn reduces output power and wall-plug efficiency. In this paper, we designed a novel epitaxial structure, which suppresses carrier leakage by inserting n-Ga0.55In0.45P and p-GaAs0.6P0.4 between barriers and waveguide layers, respectively, to modulate the energy band structure and to increase the height of barriers. The results showed that leakage current density reduced by 87.71%, compared to traditional structure. The output power reached 12.80 W with wall-plug efficiency of 78.24% at an injection current density 5 A/cm2 at room temperature. In addition, temperature drift coefficient of center wavelength was 0.206 nm/°C at the temperature range from 5 to 65 °C. The novel epitaxial structure provides a theoretical basis for achieving high-power laser diode.
The coal-fired boiler combustion process's economic, safety, and environmental performance holds great significance when constructing smart power plants. In coal-fired boiler combustion, H2S and CO are the two main high-temperature corrosive gases. They not only corrode the boiler near the wall surface but also pose severe harm to the atmospheric environment through their exhaust gases. Based on the near-infrared tunable diode laser absorption spectroscopy technology, combined with wavelength modulation spectroscopy and frequency division multiplexing technology, an unstaffed online real-time monitoring instrument for H2S and CO gas concentrations in the main combustion zone of coal-fired boilers was developed. Gas absorption spectroscopy in the 6335−6341 cm−1 range was simulated, and two near-infrared lasers near 1.5 μm were selected as the laser source. A high-temperature and corrosion-resistant Herriott-type multi-pass cell was developed to attain an effective optical path length of 15 m for the interaction between laser and gas. Hardware circuits and corresponding firmware programs were developed to attain secondary demodulation of the absorption spectroscopy signals of H2S and CO and concentration inversion. The linearity and Allan variance experiments showed linear fitting correlation coefficients of 0.9998 and 0.9995. At 73 s and 53 s integration times, the minimum detection limits for H2S and CO were 0.2×10−6 mol/mol and 0.344×10−6 mol/mol, respectively. Finally, the developed instrument was applied in the combustion atmosphere of the main combustion zone of a 300 MW coal-fired boiler under a four-corner tangential firing system, and synchronous measurements of H2S and CO near the water-cooled wall were conducted. The results indicated a positive correlation between the concentrations of H2S and CO in the boiler, with anaerobic combustion leading to an increase in the content of these gases and causing corrosion to the water-cooled wall.
The photonic integrated interferometric imaging system generally adds single-mode fiber arrays at the focal plane of the subaperture, and completes the large-field-of-view splicing imaging by receiving beams with different field-of-view angles, but the direct use of fiber arrays leads to the discontinuity of the imaging field-of-view, the focal length of the subaperture becomes longer, and the thickness is increased substantially. To address the above problems, this paper proposes a combination of microlens arrays and fiber optic arrays to subdivide the subaperture image plane to achieve a seamless splicing of the field of view, and through the combination of the telephoto objective lens and the three-lens spatial compression plate significantly reduces the overall thickness of the subaperture array. The design results show that by adding 65*65 microlens array in front of the fiber array to focus the beam twice to achieve the system field of view seamless splicing, the field of view is expanded 65 times, the full field of view is 0.0489 °, the efficiency of spatial optical coupling in the center of each fiber in the single-mode fiber array is not less than 40% when the visible light is incident, and after adding the spatial compression plate to compress the free-space light path, the overall thickness of the system achieves one order of magnitude compression. The system in the realization of photonic integrated interference imaging system large field of view seamless splicing imaging at the same time, for the solution of the problem of ultra-long focal length lens thickness is too large to provide a new way of thinking.
The study systematically analyzes the impact of various parameters such as laser repetition frequency, pulse duration, average power, water jet pressure, repeat times, nozzle offset, focal position, offset distance between grooves, and processing speed on the surface morphology of stainless steel. The findings reveal that micro-groove depth increases with higher laser power but decreases with increasing jet pressure and processing speed. Interestingly, repeat times have minimal effect on depth. On the other hand, micro-groove width increases with higher laser power and repeat times but decreases with processing speed. By optimizing these parameters, the researchers achieved high-quality pound sign-shaped trap structures with consistent dimensions. We tested the secondary electron emission coefficient of the "well" structure. The coefficient is reduced by 0.5 at most compared to before processing, effectively suppressing secondary electron emission.
To address the bottleneck that makes the conventional polarization spectral imaging method difficult to apply to the ballistic platform, a fast multi-dimensional imaging guidance optical scheme based on array optics is proposed. The correlation model between channel resolution and telescopic magnification is constructed. The precise matching and efficient utilization of the parameters of the microlens array, spectral filter array, and micro-nano-polarization array detector are realized. Based on the conventional guidance head and commercial polarization detector, a multi-dimensional imaging guidance optical system including spherical is designed. The system adopts a 4×4 optical field segmentation layout, forming 16 spectral channels through the visible light band with a spectral resolution of 16 nm. A polarization spectral data cube in four polarization directions, such as 0°, 45°, 90°, and 135° is acquired efficiently under the conditions of a single optical path and a single detector. The system has an effective focal length of 150 mm and a structure length of 145 mm. Simulation results show that the full-field modulation transfer function of the system is close to the diffraction limit at the Nyquist frequency for 16 channels. The imaging quality meets the requirements of bullet-loaded target multi-dimensional detection and identification.
Traditional cleaning methods can not clean small pollution particles on the surface of cultural relics. It can easily cause irreversible damage to the surface of cultural relics. In order to improve the ability to clean pollutants, laser cleaning technology is gradually applied to clean different types of cultural relics. This paper develop a nanosecond laser cleaning system to clean the fragments of stone artifacts in the Palace Museum. The object of the cleanout is black crust pollutants. To avoid the yellowing effect, a dual wavelength combination of 1064 nm near-infrared and 355 nm ultraviolet was used for laser cleaning of simulated marble samples. When the energy density range of these two wavelengths is 3∶2, the system of the real-time observation microstructure photos shows good cleaning effect. This ratio 3∶2 is applied for the sample of marble fragments. The micro-Raman is utilized to evaluate the cleaning effect. The above experimental results confirm the advantages of laser cleaning and also provide the reference of laser cleaning parameters and evaluation methods for laser cleaning of surface pollutants on stone cultural relics. At the same time, it also provides reference for the laser cleaning technology to clean the surface of other stone cultural relics.
In order to solve the problem of wavefront detection without ideal point beacon in adaptive optical system under strong turbulent environment, this paper proposes a method to detect the optical field information of extended beacons by using a Plenoptic sensor. The optical field imaging principle, wavefront phase reconstruction algorithm and error influence rule of extended beacons are studied. The imaging process of the extended beacon on the optical field sensor is simplified by using the equivalence method, and the optical field images are rearranged in a specific way. The wavefront reconstruction of 0° field of view is realized by image cross-correlation method and Zernike mode method. Simulation studies were carried out on error influencing factors such as different input aberration coefficients, the number of single-row microlens elements and noise. The results show that: When the input aberration is less than 6.5λ, the wavefront reconstruction accuracy is about 0.08λ. For the image detector with image resolution of 1080×1080 and pixel size of 5.5 μm, the wavefront reconstruction accuracy is the highest when the number of single row microlens units is between 40 and 50, and the system noise hardly affects the accuracy. Finally, an extended beacon wavefront detection system is built to reconstruct the four aberration wavefronts of 0° field of view by detecting the extended beacon. The wavefront reconstruction accuracy of the experimental system is about 0.04λ, which basically meets the wavefront detection requirements of the adaptive optical system.
Hydroxyl (OH) is a widely existing product in the combustion reaction process. In the combustion diagnosis technology, the two-dimensional spatial distribution based on hydroxyl is commonly used to characterize the structure of the flame front, while hydroxyl is an important parameter to characterize features such as the flame temperature, flame surface density, and heat release rate. The effective detection of hydroxyl in combustion flame is an important support for exploring the evolution of combustion dynamics and revealing the mechanism of random flame events. Planar laser-induced fluorescence (PLIF), as an optical measurement method, has the advantages of high spatial and temporal resolution, nonintrusive nature, and selection of components, and has successfully observed the structure of various combustion flames, such as Bunsen burner flame, turbulent flame, swirl flame and supersonic flame, which provides an important reference for the establishment of combustion models. This paper starts with the basic principle of PLIF detection, reviews the development history and research status of PLIF technology in the field of combustion diagnosis, introduces the PLIF ultraviolet light source technology based on dye laser, optical parametric oscillation and Ti:sapphire tripling-frequency, and discusses the characteristics of different technical routes. Finally, the development of UV laser technology for OH-PLIF is prospected.
In order to adapt to the complex dynamic changing wake bubble field environment, the detection signal-to-noise ratio and detection rate of ship wake weak signal are improved, and the detection range is expanded.
In this paper, a detection method of ship wake weak signals based on synchronous accumulation method is proposed. By taking advantage of the repeatability of periodic signals and the randomness of noise, cumulative normalization is performed on successive periodic signals, which can effectively improve the detection signal-to-noise ratio and reduce the interference of random signals on detection performance. In order to evaluate the detection performance of the algorithm under multi-parameter coupling, a multi-time scale detection capability evaluation model for ship wake weak signals is established.
By conducting a large number of simulated ship wake detection experiments in indoor large pools and outdoor typical lakes, it is verified that the algorithm is suitable for the detection of sparse and discrete tiny far-field wake bubbles to large-scale near-field bubbles under high turbulence disturbance, thus realizing the full-time ship wake tracking and detection and effectively improving the underwater weapon strike capability.
It can provide support for ship wake laser detection and identification engineering practice.
In order to accurately measure the three-dimensional surface shape of object, the influence of sampling on it was studied. Firstly, on the basis of deriving spectra expressions through Fourier transform, the generation of CCD pixels was analyzed and its expression was given. Then, basing on the discrete expression of deformation fringes obtained after sampling, its Fourier spectrum expression was derived, resulting in an infinitely repeated "spectra island" in the frequency domain. Finally, on the basis of using a low-pass filter to remove high-order harmonic components and retaining only one fundamental frequency component, the signal strength is reconstructed by inverse Fourier transform. A method of reducing the sampling interval, i.e. reducing the number of sampling points per fringe, was proposed to increase the ratio between the sampling frequency and the fundamental frequency of the grating, so as to more accurately reconstruct the object surface shape under the condition of
Laser communication utilizes light waves as the transmission medium. It offers many advantages, including high data rates, expansive bandwidth, compactness, robust interference resistance, and superior confidentiality. It has the critical capability to enable high-speed transmission and secure operation of space information networks. Prominent research institutions have committed to studying a series of challenges that need to be solved in the process of networking laser communication technology, including point-to-multipoint simultaneous laser communication, all-optical switching and forwarding of multi-channel signals within nodes, node dynamic random access, and network topology design. Numerous demonstration and verification experiments have been conducted, with a subset of these research results finding practical applications. Based on the analysis and discussion of space laser communication networking technology, this paper summarizes the development of laser communication networking technology both domestically and internationally, focusing on the application of laser communication networking technology in the fields of satellite constellations, satellite relays, and aviation networks; furthermore, it presents a review of pertinent domestic research methodologies, experimental validations, and technical solutions; finally, it predicts the development trend of laser communication networking technology and applications.
To address the issues of blurred edge details and poor contrast in multi-scale transform fused images obtained using remote sensing detection methods for mixed background features, an image fusion approach that combines the sparse representation of non-downsampled contour wavelet transform and a guided filter was utilised to enhance the quality and visual appearance of the fused images. This method involved several steps: Firstly, a multi-scale and multi-directional decomposition was performed on both spectral and polarimetric images using non-downsampled contour wavelet transform to isolate the feature information in each subband; secondly, the low-frequency subbands were fused using a sparse representation approach to minimize the loss of contrast in the fused image; additionally, the high-frequency subbands were fused through a bootstrap filter to enhance the detail information and the contours of the image; finally, the low-frequency and high-frequency fusion coefficients were inverted using non-downsampled contour wavelet inversion to generate the final fused image. Analysis indicates that this method has increased the contrast of the fused image by up to 54.5% relative to the original spectral image and by 15.4% compared to the polarimetric image. This has resulted in a fused image in which it is easier to distinguish objects in shadows within a mixed background. This method was used to fuse spectral and polarimetric images captured by a polarimetric spectral imager at different wavelengths, which resulted in true-colour reproduction. These true-colour restored images demonstrate that this fusion method retains environmental information within the mixed background while distinguishing the object from the background, effectively improving the image quality of polarization spectral remote sensing detection imaging. This approach enhances the integrity and authenticity of image information in polarization spectral remote sensing detection imaging, thereby expanding its application scope in remote sensing detection of complex environments and image recognition.
With the rapid advancement of spectral imaging technology, the use of multispectral filter array (MSFA) to collect the spatial and spectral information of multispectral images has become a research hotspot. The uses of the original data are limited because of its low sampling rate and strong spectral inter-correlation for reconstruction. Therefore, this paper proposes a multi-branch attention residual network model for spatial-spectral association based on an 8-band 4 × 4 MSFA with all-pass bands. First, the multi-branch model was used to learn the image features after interpolation in each band; second, the feature information of the eight bands and the all-pass band were united by the spatial channel attention model designed in this paper, and the application of multi-layer convolution and the convolutional attention module and the use of residual compensation effectively compensated the color difference of each band and enriched the edge texture-related feature information; finally, the preliminary interpolated full-pass band and the rest of the band feature information were used in feature learning by residual dense blocks without batch normalization on the spatial and spectral correlation of multispectral images to match the spectral information of each band. Experimental results show that the peak signal-to-noise ratio, structural similarity, and spectral angular similarity of the test image under the D65 light source outperform the state-of-the-art deep learning method by 3.46%, 0.27%, and 6%, respectively; in conclusion, this method not only reduces artifacts but also obtains more texture details.
This study proposes an active polarization imaging approach that utilizes laser illumination to tackle the issue of low target detection contrast in strong light backgrounds, which is a challenge in conventional photoelectric detection. The study examines the coupling relationship between the polarization characteristics of three typical target materials and the scattering angle of a laser beam. This is achieved by constructing a laser incident bidirectional reflection distribution model, a laser incident polarization bidirectional reflection distribution model, and a target surface polarization model of laser illumination. Backlight observation experiments are conducted in a controlled darkroom to verify the impact of the scattering angle of the laser beam on the polarization characteristics of the target. The experimental results show an 86.11% increase in target contrast for active polarization imaging under strong light background compared to traditional passive intensity imaging. Additionally, different target materials exhibit differing visible polarization characteristics under varying beam dispersion angles, with metallic materials is higher than that of non-metallic materials. This result aligns with theoretical analysis and support the advantages of active polarization imaging. The outdoor solar backlight observation experiment verifies the applicability of the research method in high-intensity light and long-distance settings. This study can lay a theoretical foundation for improving accurate target perception under a strong light background.
The Terahertz wave possesses characteristics of high penetration, low energy, and fingerprint spectrum, etc., making it widely used in the detection field. Therefore, developing a Terahertz wave detection optical imaging system holds substantial significance and wide application prospects. Firstly, we refer to the structure of Tessar objective lens, which consists four lenses. The balance equations of aberration for the system were established through the application of the aberration theory of the paraxial optical system. Subsequently, we provide a solution function and method of the initial structure parameters of the system. Then, we combine it with optical design software to further correct the aberration of the system. Finally, we design a Terahertz wave detection optical imaging system with a large aperture. The optical system consists of four coaxial refractive lenses with a total focal length of 70 mm, an F-number of 1.4, and a full field of view angle of 8°. The value of modulation transfer function (MTF) in the range of full field of view angle is greater than 0.32 at the Nyquist frequency of 10 lp/mm, and the root mean square (RMS) radius of the diffused spot in each field of view is less than the airy disk radius. Finally, the paper analyzes and discusses the various tolerance types of the system. The results indicate that the Terahertz wave detection optical imaging system, designed in this paper, has a large aperture, a simple, compact form, a lightweight structure, excellent imaging performance and simple processing, which meets the design requirements, and it has important applications in the field of high-resolution detection and other fields within the Terahertz wave band.
Ghost images, as a type of stray light, are caused by residual reflected light between the optical surfaces. These images can degrade image clarity, annihilation targets, and severely affect the performance of optical systems. To investigate the impact of ghost images on optical system performance, we developed a Modulation Transfer Function (MTF) calculation model under the influence of ghost images generated by secondary reflection. This paper first introduces the method of analyzing and describing using the paraxial approximation. Then, starting from the definition of the MTF, and considering the influence of ghost image irradiance on the modulation of the image plane, a calculation model for calculating the MTF under the influence of ghost images is constructed. After performing calculations and comparing them to simulation results, it was found that the maximum mean square error was less than 0.049373, which verifies the accuracy of the model. Furthermore, a detailed analysis was conducted, examining cases that exhibited larger errors and clarifying the range in which this calculation method can be applied The research results indicate that the paraxial approximation method is both accurate and reliable when calculating the MTF under the influence of ghost images is accurate, and is applicable in most cases. This study serves as a valuable exploration in the ghost image analysis of optical systems.
Bright-field imaging can provide cellular and histological morphological information, while fluorescence imaging can provide expression information of key proteins. Dual-modal correlation imaging based on both techniques is currently a common method for examining tissue samples in medical and scientific research. In clinical examination, however, correlation imaging between adjacent tissue slices is often used for observation. In such cases, both the tissue structure and the cellular level may be altered more or less, which is unfavorable when the sample volume is insufficient, the number of cells on the slices is limited, or precise point-to-point morphological information is required. Therefore, the development of single-slice dual-modal optical correlation imaging techniques which provides both tissue morphology and the distribution and expression of multiple target proteins on a single slice, can help to more accurately describe tumors and their microenvironment. This technique is particularly important in renal pathological testing where sample size is small. Renal pathology requires the use of bright-field imaging to obtain pathomorphological information of tissues and cells after hematoxylin-eosin staining, while the use of fluorescence imaging to obtain the distribution and expression of multiple target proteins is a mandatory molecular test for renal pathology screening. This paper focuses on the tissue sample processing methods that allow the coexistence of hematoxylin-eosin staining and immunofluorescence staining on the same renal slice. Improvements and comparative evaluations of the staining, de-colorizing and re-staining processes, as well as innovative fusion techniques for single-slice dual-modal imaging.
In order to meet the requirements of the national synchrotron radiation source, the anisotropic wet-etching technology of small blazed angle monocrystalline silicon grating is studied, and the blazed grating suitable for the medium wave soft X-ray band is prepared. Based on the rigorously coupled wave theory, the structural parameters and process tolerance of the small blazed angle grating are designed. In the crystal alignment process, the crystal orientation of the silicon wafer is determined by ring-preetching, and then the grating mask is aligned with the crystal direction of monocrystalline silicon <111> based on the frequency doubling adjustment method. At the same time, the effect of the photoresist ashing technique and the active agent on the groove quality of the grating is investigated, and the scintillating gratings close to the ideal sawtooth groove shape are successfully prepared by the monocrystalline silicon anisotropic wet etching process. The experimental results show that the blazed angle of the prepared grating is 1°, the linear density is 1200 gr/mm, and the root mean square roughness of the blazed surface is less than 0.5nm. This method can be applied to the fabrication of the medium wave soft X-ray band blazed grating, which can greatly reduce the difficulty and cost of fabrication while achieving high diffraction efficiency.
Mid-spatial frequency surface errors (MSFSE) can cause small angle scattering in optical systems. In order to determine a reasonable tolerance for MSFSE in optical design and processing, this paper conducts a quantitative study on the impact of MSFSE on the modulation transfer function (MTF) of optical systems. Under diffraction-limited conditions, we derived an expression for the influence of MSFSE on the MTF of optical systems and analyzed it. Then, we verified the theoretical derivation results through optical design software simulation. Assuming that the optical system has a sinusoidal MSFSE on the pupil, we performed the Fourier transform on the pupil function and squared it to obtain the point spread function (PSF), and then performed the Fourier transform on the PSF to obtain the optical transfer function (OTF) of the optical system. By taking the OTF mode, the expression of MTF under the influence of MSFSE can be obtained. By comparing this expression of MTF with the MTF of an optical system without MSFSE under diffraction-limited conditions, the quantitative impact of MSFSE on the MTF of the optical system can be obtained. Theoretical calculation results indicate that sinusoidal MSFSE can lead to different losses of MTF at different spatial frequencies and that the changes in MTF losses are periodic. The maximum loss ratios of MTF in optical systems caused by sinusoidal MSFSE with peak-to-valley (PV) of 0.030 μm, 0.095 μm, 0.159 μm and 0.223 μm are 0.89 %, 8.80 %, 23.48 % and 43.31 %, respectively. The loss of MTF will increase nonlinearly with the increase of PV of MSFSE. The theoretical calculation results are consistent with the software simulation results.
For the first time, Tb3+ and Dy3+ co-doped AlN films were prepared using ion implantation, and their crystal structure, cathodoluminescence properties and energy transfer mechanism were investigated. Raman scattering and X-ray diffraction results indicate that ion implantation of Dy3+ has caused increased compressive stress within the internal lattice when the dosage of Tb3+ remains constant. Continuous implantation led to the recombination of some point defects, resulting in a partial release of internal compressive stress. Cathodoluminescence spectra demonstrated that with high-dose Tb3+ implantation, the emission intensities of Tb3+ and Dy3+ exhibited different trends with increasing Dy3+ dosage. We propose the existence of a resonance energy transfer from Tb3+ ions 5D4→7F6 to Dy3+ ions 6H15/2→4F9/2 in AlN films. Finally, we observe that under different implantation dose of Dy3+ ions to Tb3+ ions, the emission color of the sample shifts between yellow-green and orange-yellow, with color temperatures ranging from 4042 to 5119K. Adjusting the dose ratio of Dy3+ to Tb3+ enables effective control of chromaticity coordinates and color temperatures.
Focusing on the influence of the matrix lattice anisotropy on the polarization luminescence of rare earth ions, ZnO microrods and europium-doped ZnO microrods were prepared using a hydrothermal method. Comparative studies have found that the length-to-diameter ratio of doped samples increases, and the morphology of the microrod changes from dumbbell-like to straight. Analysis of the optical properties shows that the bound exciton luminescence at 385-nm makes the UV luminescence of ZnO microrods appear asymmetrical, and a weak luminescence in visible region is observed at 550 nm. After europium ion doping, the luminescence in the visible region is enhanced. For Eu3+ doped ZnO microrods, Eu3+ ion characteristic luminescence peaks with narrow half width can be observed under 532-nm excitation. When the polarization direction of the incident excitation light is adjusted, the emission of Eu3+ ions changes periodically with the angle of the polarized light. The polarization degree increases as the doping concentration increases. These results show that the luminescence of the europium ions in the ZnO microrod matrix lattice is sensitive to the polarization of excited light. Doped ZnO microrods can integrate the ultraviolet absorption properties of low-dimensional ZnO materials with the excellent visible luminescence properties of rare earth ions, meaning they have significant application value in fields such as polarization detection.
There is a significant narrowing of the lateral radiation spectrum of the substrate of organic light-emitting diodes as compared to the forward radiation spectrum. Studying the factors that affect the lateral radiation spectrum narrowing of the device and further reducing the spectral linewidth can provide a foundation for the study of the electrically pumped organic light-emitting diode laser radiation. We study the full width at half maximum, peak wavelength, and polarization characteristics of lateral radiation spectrum in organic light-emitting diode substrate, with the thickness changes of hole transport layer NPB. The lateral radiation spectra of organic light-emitting diode with Ag film evaporated on both sides of the substrate edge are compared with those of organic light-emitting diode without Ag film. The full width at half maximum of the lateral radiation spectrum with Ag film is narrower. When the NPB thickness is 130 nm, the full width at half maximum of the lateral radiation spectrum in the device substrate reaches its narrowest, which is 14 nm. This shows that the optical resonator will affect the light propagating laterally in an organic light-emitting diode substrate when mirrors are provided on both edge sides of the substrate. The results indicate new approaches to narrowing the radiation spectrum and amplifying the light of organic light-emitting diodes.
In this paper, a terahertz band-stop filter based on a symmetrical H-type structure was designed, the continuous metal arms of which can flow current. By using electromagnetic simulation software CST Microwave Studio 2021, the filtering characteristics of the filter were studied, and the geometric parameters of the filter were determined by changing the arm length, period length and gap of double H. The results show that the filter can realize the tunable polarization properties. Under the
Passively Q-switched mode-locked operation was realized for the first time by inserting a semiconductor saturable absorption mirror (SESAM) as a mode-locking element into a Tm:CaYALO4(Tm:CYA) laser using tandem-pumping technology. The laser cavity adopted an X-type four-mirror cavity structure, and the pumping source was an Er:Y3Al5O12(Er:YAG) solid-state laser with a central wavelength of 1650 nm. Output coupling mirrors with transmittances of 0.5%, 1.5%, 3%, and 5% were used to study the laser’s continuous wave (CW) output and mode-locking output characteristics. The experimental results show that the laser has the best output characteristics when an output coupling mirror with a transmittance of 5% is used. The maximum power of 894 mW and the maximum slope efficiency of 16% were obtained when the laser operated in the CW regime. After the CW power was optimized to the highest, the mode-locked element SESAM was added to the optical path. When the absorbed pump power became greater than 1.86 W, the laser operation entered an unstable Q-switched state; when the absorbed pump power increased to 5.7 W, a stable passively Q-switched mode-locked operation was achieved; when the absorbed pump power reached 6.99 W, a mode-locked pulse laser with a maximum output power of 399 mW was obtained by using the output coupling mirror with transmittance of 5%. At that time, the repetition frequency under the Q-switched envelope was 98.11 MHz, the pulse width was 619.4 ps, and the corresponding maximum single pulse energy was 4.07 nJ. The mode-locked pulse modulation depth in a Q-switched envelope was observed to be close to 100%. The above results show that tandem-pumping technology can be used in lasers to generate Q-switched mode-locked pulses, which provides a new pumping method for generating ultrashort pulse lasers.
We investigate a silicon-glass fiber-optic Fabry-Perot (FP) pressure sensor based on Micro-Electro-Mechanical Systems (MEMS) technology for high-pressure measurements. Silicon material was used as the sensitive element, and the Inductively Coupled Plasma (ICP) dry-etched monocrystalline silicon diaphragm was anode bonded with a high borosilicate glass to form the FP cavity. The sensor head was manufactured in batches utilizing MEMS technology, which is structurally stable, strongly resistant to overload, and not prone to fail in high-pressure environments. The experimental results show that the sensor can acheive high-pressure measurements up to 30 MPa with a sensitivity of 46.94 nm/MPa and a linearity of 0.99897, with high consistency and reliable measurement results. The designed pressure sensor has strong application prospects in high-pressure sensing.
Cascaded Microring Resonators (CMRR), a new type of optical sensor, are widely used in biology, medicine, and other fields because of their high sensitivity, easy integration, and low power consumption. In this paper, we propose a Python-based envelope fitting method for real-time CMRR sensor’s output spectrum to achieve real-time data analysis and processing of the CMRR sensor’s output spectrum. First, different fitting models were used to fit the output spectrum of the CMRR sensor. Then, the fitting errors of different fitting models were compared by sensitivity error percentage, and it was concluded that the smooth spline fitting method performed best in real-time processing of the output spectrum of the CMRR sensor. Finally, NaCl solution with different concentrations was used for real-time acquisition and processing of the output spectrum. The reliability of the real-time acquisition and processing program for the CMRR sensor’s output spectrum is verified. The experimental results show that the wavelength drift of the CMRR sensor is linearly related to the concentration of the solution. It can be seen from the calculation that the sensitivity of the CMRR sensor for brine is about 671.03529 nm/RIU.
In this paper, we developed a dual-sideband beat-suppressed heterodyne phase-sensitive dispersion spectroscopy (HPSDS) for sensitive detection of trace gases across a wide dynamic range and explored the operational characteristics of the electro-optic modulator (EOM) and bias voltage control methods under sideband suppression mode. The dispersion phase spectral profiles and the corresponding signal-to-noise ratios in both suppression and non-suppression modes were compared before a comprehensive evaluation of the detection performance. A HPSDS-based detection system was developed based on a near-infrared distributed feedback laser and an EOM. The suppression of the dual-sideband beat was achieved by exploring and analyzing the optimal operational range of the EOM, leading to the optimization of dispersion phase signals with increased amplitude and high signal-to-noise ratio. The dispersion phase signals under typical high-frequency (1.2 GHz) intensity modulation were recorded for different standard methane/nitrogen mixtures. The relationship between the peak-to-peak values of the dispersion phase signals and the varied gas concentrations was then summarized. Meanwhile, wavelength modulation spectroscopy (WMS) experiments were conducted; subsequently, the HPSDS and WMS techniques’ performances were compared in terms of linearity, dynamic detection range, and immunity to optical power fluctuations. Finally, the HPSDS-based system's performance under a wide dynamic range and rapid time response was verified by measuring different concentrations of standard gases. Experimental results indicate that the HPSDS technique exhibits high linearity (
We use an electro-optical potential phase modulator to modulate the pump light to obtain radio frequency modulation transfer spectroscopy (MTS), and study the optimization problem of the zero-crossing slope of the center of the dispersive signal of the MTS spectrum. By changing the modulation frequency of the pump light, the spot size of the pump light and the probe light, we study the parameter dependence between the zero-crossing slope of the MTS spectral signal and the modulation frequency, and spot size. The optimal MTS spectral signal is obtained when the pump light modulation frequency is −3.6 MHz (about 0.69 times the natural linewidth). Finally, by using the optimal MTS spectrum, the DL Pro @ 852 nm laser frequency is locked to the cesium atom D2 line (F = 4) - (F = 5') cycle transition, and the laser frequency fluctuation is about 170 kHz in the 60 minutes sampling time, which is significantly improved compared with the frequency fluctuation of the laser −11 MHz during free running.
Aiming at the loss of target point information caused by the degradation of underwater calibration images collected by camera calibration in underwater visual measurement, an underwater calibration image enhancement algorithm based on image block decomposition and fusion is proposed. First, given the difficulty of image dehazing caused by uneven illumination of underwater calibration images, image segmentation is implemented based on homomorphic filtering to calculate the global background light intensity and to achieve image dehazing. Then, given the problems such as noise, blur, and uneven illumination that still exist after the underwater image is dehazed, contrast enhancement and detail information enhancement are performed to obtain two complementary enhanced images. The complementary images are divided into multiple image blocks, and the image blocks are decomposed into three independent components, each of which is average intensity, signal intensity, and signal structure. The three components are separately fused and solved for the final enhanced image. Finally, subjective and objective evaluation and target point detection experiments are used to evaluate the enhanced quality of the underwater calibration image. Experimental results indicate that the visual effects and evaluation scores of the proposed method are higher than those of UDCP, MSR, and ACDC methods. When the turbidity is 7.6 NTU, 11.4 NTU, 15.7 NTU, and 18.4 NTU, the number of detected target points increases by 2.0%, 2.3%, 9.3%, and 21.2%. Therefore, we present a reliable and effective method to improve the quality of underwater calibration images and provides a stable and reliable underwater calibration image enhancement method for underwater visual measurement.
This paper focuses on the comprehensive detection of defects in cold rolled steel through examination for surface and internal defects. Regarding surface defect detection, a bilateral line light illumination scheme is proposed and a comparison with line light illumination scheme is carried out. As for internal defect detection, the applicability of various metal internal inspection technologies such as X-ray, ultrasound, and infrared thermography is analyzed from the perspectives of detection resolution and defect edge characteristics. The results show that bilateral line light illumination not only increases the overall average precision of the YOLOv5 object detection algorithm model to 90.16% (an increase of 15.46% compared to the line light illumination) but also improves model classification and training efficiency. X-ray and ultrasound inspection technologies can detect blind holes with a diameter of 0.25 mm, while infrared thermography can detect blind holes with a diameter of 1 mm. In evaluating defect edge characteristics, X-ray inspection technology exhibits a minimum blind hole edge grayscale difference of 145, ultrasound of 89, and infrared thermography of 30. This study proposes an improved scheme for the detection of surface defects in cold rolled steel and offers insights for the research on internal defect detection.
Linear optical processors based on the cascaded topology of Mach-Zehnder Interferometer (MZI) have been demonstrated to be an important way of implementing Optical Neural Networks (ONN), but several practical challenges still need resolution. Concerning issues arising from chip manufacturing and testing processes that could lead to phase errors and insertion losses, we conducted experiments and theoretical simulations for various reconfigurable optical processors. We found that the weights of any arbitrary unitary matrix can be realized through some single
Strain reconstruction is a vital component in the characterization of mechanical properties of phase-contrast optical coherence tomography (PC-OCT). It requires an accurate calculation for gradient distributions on the differential wrapped phase map. In order to address the challenge of low signal-to-noise ratio (SNR) in phase gradient calculation under severe noise interference, a Bayesian-neural-network-based phase gradient calculation is presented. Initially, wrapped phase maps with varying levels of speckle noise and their corresponding ideal phase gradient distributions are generated through a computer simulation. These wrapped phase maps and phase gradient distributions serve as the training datasets. Subsequently, the network learns the “end-to-end” relationship between the wrapped phase maps and phase gradient distributions in a noisy environment by utilizing a Bayesian inference theory. Finally, the wrapped phase measured by PC-OCT is processed by Bayesian neural network (BNN), and the high-quality distribution of phase gradients is accurately predicted by inputting the measured wrapped phase-difference maps into the network. Additionally, the statistical process introduced by BNN allows for the utilization of model uncertainty in the quantitative assessment of the network predictions’ reliability. Computer simulation and three-point bending mechanical loading experiment compare the performance of the BNN and the popular vector method. The results indicate that the BNN can enhance the SNR of estimated phase gradients by 8% in the presence of low noise levels. Importantly, the BNN successfully recovers the phase gradients that the vector method is unable to calculate due to the unresolved phase fringes in the presence of strong noise. Moreover, the BNN model uncertainty can be used to quantitatively analyze the prediction errors. It is expected that the contribution of this work can offer effective strain estimation for PC-OCT, enabling the internal mechanical property characterization to become high-quality and high-reliability.
Non-destructive, non-contact phase-shifting digital holography technology has distinct advantages in identifying micro-optical components. As traditional phase-shifting digital holography technology requires fine control and cumbersome calibration of the phase shifter, furthermore, its optical path is susceptible to mechanical vibration interference, which reduces the quality of the holographically reproduced image. To solve the above problems, we propose a vortex phase-shifting digital holography for the micro-optical element surface measurement with the help of the special phase distribution of vortex light. The method utilizes a helical phase plate to modulate the vortex phase and introduce a high-precision phase shift. Based on the constructed vortex phase-shifting digital holographic microscopy experimental setup, the actual phase shifts between phase-shift interferograms were determined using the interferometric polarity method, the relationship between the rotation angle of the helical phase plate and the phase shift was calibrated, and the feasibility of the vortex phase shift was experimentally verified. Repeated measurement experiments were carried out on the micro-lens arrays, and the measurement results were compared with those of the ZYGO white light interferometer. The results indicate that a single micro-lens's average longitudinal vector height is 12.897 μm with an average relative error of 0.155%. The proposed method enables highly precise measurement of the surface topography of micro-optical elements. It offers the advantages of easy operation, high stability, and high accuracy.
The reconstruction of the three-dimensional surface morphology of objects based on binocular stereo matching is constrained by physical conditions such as sensor size, lens focal length, and environmental light. A binocular surface three-dimensional reconstruction method based on interpolation super-resolution is proposed in response to this issue. First, at the image preprocessing stage, an image enhancement method based on wavelet transform and dual histogram equalization fusion is established to overcome the problems of traditional binocular vision limited by complex environmental light interference. Second, a super-resolution algorithm based on Lagrange and cubic polynomial interpolation is constructed to increase the image’s pixel density and add image details to the binocular matching cost calculation stage, thereby improving the matching accuracy. Finally, a simple linear iterative clustering (SLIC) method is used to segment the target image, and a secondary surface fitting is performed for each segmented area to obtain a height curve that is more closely aligned with the actual surface of the object, which can reduce the reconstruction error and improve the reconstruction accuracy. The experimental results show that the average relative error of the global height measurement of 5 sets of measurement samples is ±2.3%, the average measurement time of the experiment is 1.8828 s, and the maximum time is 1.9362 s. This is a significant improvement over traditional methods. Experimental analysis results verify the effectiveness of the proposed algorithm.
We propose an improved point cloud registration method based on point-by-point forward feature point extraction to improve the efficiency and accuracy of point cloud registration. Firstly, the point-by-point forward method was used to quickly extract the point cloud feature points, significantly reducing the number of point clouds while retaining the characteristics of the point cloud model. Then, the improved KN-4PCS algorithm using normal vector constraints was coarsely registered to achieve the preliminary registration of the source point cloud and the target point cloud. Finally, the two-way Kd-tree optimized LM-ICP algorithm was used to complete the fine registration. In this paper, registration experiments were conducted on different point cloud data. In the registration experiment on Stanford University open point cloud data, the average error was reduced by about 70.2% compared with the SAC-IA+ICP algorithm, about 49.6% compared with the NDT+ICP algorithm, and the registration time was reduced by about 86.2% and 81.9%, respectively, while maintaining high accuracy and lower time consumption after introducing different degrees of Gaussian noise. In the point cloud registration experiment on real indoor objects, the average registration error was 0.0742 mm, and the average algorithm time was 0.572 s. The experimental results show that the proposed method can effectively improve the point cloud registration’s efficiency, accuracy, and robustness, thereby providing a solid foundation for indoor target recognition and pose estimation based on the point cloud.
Accurate droplet edge extraction is crucial for measuring water contact angle. To address issues like poor noise robustness, incomplete edge extraction, and low precision in conventional methods, we propose an improved model for droplet edge detection based on Richer Convolutional Feature (RCF) algorithm. Firstly, a feature fusion module is introduced in the deep feature extraction stage to enhance model robustness and reduce overfitting risks. Secondly, a multi-receptive field module replaces the contact layer after RCF to extract more semantic information and enrich edge details. Thirdly, an efficient channel attention mechanism is introduced before each layer of the models to enhance focus on important features of the image. Lastly, the MaxBlurPool downsampling technique is designed and incorporated to reduce computation and parameter requirements while improving translation invariance. Experimental results on a self-made droplet dataset demonstrate that the proposed model achieves an ODS value of 0.816, an OIS value of 0.829, and a detection accuracy of up to 90.17%, which is an improvement of 1.85 percentage points compared to the original model. It can improve accuracy in droplet edge features detections.
Space-borne two-dimensional turntables are the main bearing mechanism of space cameras and other optoelectronic equipment, and the U-frame is the key supporting part of these turntables. In order to optimize the structure and lightweight design of the U-frame of the two-dimensional turntable and to develop a lightweight two-dimensional turntable with a high load-bearing ratio, we design a U-frame for the space two-dimensional turntable based on Carbon Fiber Reinforce Plastics (CFRP). First, a variable cross-section tubular structure U-frame was designed using carbon fiber composites instead of titanium alloy material considering the manufacturability. Then, according to the finite element modeling method based on the lay-up process, the carbon fiber U-frame was subjected to finite element modeling and simulation analysis. Then, a prototype U-frame was fabricated, and modal tests verified the accuracy of the finite element model. Finally, a three-level optimization method combining theoretical analysis, genetic algorithm, and the finite element method was proposed to optimize the design of carbon fiber U-frame ply angle, ply thickness, and ply sequence. The results indicate that the vibration patterns of the U-frame obtained from the modal test and simulation are identical and that the frequency difference is less than 5%. The initial design of the carbon fiber U-frame is 45.7% lighter than the titanium U-frame. Through the secondary optimization of the composite layup, the U-frame is further reduced in weight by 13.8%. Additionally, the intrinsic frequency of the U-frame is improved by 10.14%. It can be concluded that the composite modeling and optimization methods used in this paper are correct, and the designed carbon fiber U-frame meets the lightweight design requirements of space-born two-dimensional turntable.
The alignment accuracy of the emitting and receiving optical axes of laser communication equipment in the satellite ground field is crucial. Temperature fluctuation can cause deformations of optical components and mechanical structures, affecting the optical axis’ alignment and reducing the system’s detection accuracy. We design a high-precision optical axis stability system for detection. First, according to the technical requirements of broadband and conjugate imaging, an off-axis reflective Keplerian telescope system with image transfer was applied to compress the beam. After passing through a beam splitter, the beams entered the detection subunit separately. A long focal length optical axis stability detection system was designed to improve detection accuracy. To correct the thermal difference of the reflective system, an optical passive non-thermalization technique was employed using a refractive mirror group to compensate for the thermal-induced aberration of the reflective mirror group. The mechanical structure was designed and subjected to finite element analysis. Finite element data were processed and fed into optical software to simulate the optical axis deviation angle caused by temperature fluctuation. Finally, experiments were conducted for validation. The results show that the optical axis stability detection system has an optical axis deviation angle of 3.90" at −10 °C and 4.23" at 45 °C, reducing the impact of temperature fluctuation on optical axis deviation.
In order to achieve a large image plane and large zoom ratio in microscopic imaging and solve the problem of the high integration of coaxial Kohler illumination, we propose a design method for a compact optical system with a large zoom ratio based on coaxial Kohler illumination. First, the imaging principle of the continuous zoom optical system of telescopes and microscopes is analyzed, and the design principle of the positive group compensation zoom microscope is analyzed theoretically. Then, the front fixed group is divided into a collimation group and a convergence group, and a beam splitter prism is designed between the two lens groups to achieve a compact coaxial Kohler illumination optical system by sharing lens groups. Finally, the continuous zoom microscope with a large image plane and the matched coaxial Kohler illumination optical system are designed. The design results show that the zoom ratio of the microscope optical system is 10×, the working distance is 60 mm, the highest resolution of the object side is 1.75 µm, and the coaxial illumination uniformity is 94.3%. The designed microscope has excellent imaging quality, minimal distortion, a smooth zoom curve, and a compact size, verifying the feasibility of the design method.
Spectral synthesis technology is an important technical approach to achieving high-energy laser output. Ensuring high-quality laser output under the premise of high-power output has become the most urgent goal in further developing spectral synthesis technology. Aiming at the challenge of parameter detection for 155 mm × 140 mm rectangular aperture, (1064 ± 3) nm, (1030 ± 3) nm, and (635 ± 5) nm band beams, we design a large-aperture multi-band multi-parameter detection system. The wavefront detection unit is based on Kepler’s telescopic structure, the conjugate relationship between the deformable mirror and the microlens is constructed, at the same time, the compressed beam matches the detector size. The front group objective lenses adopt a Cassegrain structure to solve the problem of color difference correction in large-aperture and multi-band. The rear group of mirrors adopts a three-piece apochromatic refractor group, which compensates for the color difference while accounting for the non-thermal design. It can be used for compensation to the residual thermal difference of the front group of objectives and the thermal difference of the rear group of mirrors. After passing through the wavefront detection unit, the beam quality and beam uniformity can be measured. In order to improve the environmental adaptability of the system, it was designed through an optical passive anthermic method at 20 °C±10 °C. Finally, the system was installed and tested, and the wavefront spot image collected by the wavefront detection camera was restored using the Zernike wavefront restoration method. The measured RMS value of the wavefront of the system is better than 0.0524λ (λ=632.8 nm), the beam uniformity is better than 0.893, and the beam quality
Noise Figure (NF) is an important parameter in evaluating the performance of transmitting a signal from a high-frequency electronic device. As the operating frequency increases, the NF of high-frequency electronic devices usually increases, and the Excess Noise Ratio (ENR) of existing noise sources cannot meet the associated measurement requirements. Therefore, to meet the measurement requirements for the NF of high-frequency electronic devices, we propose combining three incoherent optical beams into an unitraveling carrier photodiode (UTC-PD) based on incoherent optical mixing technology. A tunable terahertz (THz) photonics noise source with a high ENR in the 220−325 GHz frequency range is developed. The ENR can be tuned up to 45 dB. By using the Y-factor method, the proposed THz photonics noise source is applied to measure a THz mixer with large NF and negative conversion gain. The measured NF of the THz mixer ranges from 16 to 32 dB, the conversion gain is about −13 dB, and the uncertainty is 0.43 dB. The tunable THz photonics noise source with high ENR can meet the measurement requirements of THz electronic devices with high NF. It will play an important role in the measurement of NF of THz electronic devices and in guiding further optimization.
A phase noise suppression algorithm based on real-imaginary-alternate pilots was proposed for a coherent optical orthogonal frequency division multiplexing communication system with offset quadrature amplitude modulation (CO-OFDM-OQAM). The algorithm uses the properties of laser phase noise and the intrinsic imaginary interference (IMI) symmetry law to design real-imaginary-alternate pilots. In combination with a linear fitting, it can accurately estimate the common phase error (CPE) for CO-OFDM-OQAM. As the compensation was performed in the frequency domain, the computational complexity was significantly reduced compared to the time-domain phase noise suppression algorithms. A numerical simulation platform was built for a polarization multiplexed CO-OFDM-OQAM system with an effective bit rate of 65 GBits/s. Through it, the transmission performance of the system with different laser linewidths and numbers of subcarriers was studied, and the suppression effect of the proposed method on phase noise was examined. The results obtained confirm that the linewidths required to reach the FEC limit for BER are equal to 801.1, 349, and 138.4 kHz for a fixed OSNR of 25 dB and a total number of subcarriers of 256, 512, and 1024, respectively. For the system using a 16-QAM modulation format with 256 or 512 subcarriers, it compensates well for the laser phase noise without affecting the power peak-to-average ratio.
This paper aims to improve the control performance of the precision tracking system for laser communication by studying the control method of Fast Steering Mirrors (FSM) driven by a voice coil motor. FSM often face the problems of strong cross-coupling characteristics and external disturbances. To overcome these challenges, we propose a composite fast nonsingular terminal sliding mode control strategy integrating feedforward decoupling compensation and fixed-time extended state observer. First, the FSM’s coupling transfer function matrix model with double inputs and double outputs is established by using the system identification method, and the feedforward decoupling compensator is designed to compensate for the coupling components and achieve motion decoupling between the
To address issues such as uneven illumination in coronary angiography images, low contrast between vascular structures and background regions, and the complexity of coronary vascular topology, we establish a coronary angiography vascular segmentation annotation dataset. Additionally, we propose a coronary angiography image vascular segmentation model based on the feature map pyramid. On the basis of the U-Net architecture, this model was improved and optimized. First, the first convolutional layer in the U-Net encoding part was replaced with a 7×7 convolutional layer to increase the receptive field of each layer. Modified ConvNeXt blocks were added to the encoding and decoding layers to enhance the network's ability to extract deeper-level features. Second, a Group Attention (GA) mechanism module was designed and incorporated at the U-Net skip connection to strengthen the features extracted from the encoding part, addressing semantic gaps between the encoder and decoder. Finally, a Pyramid Feature Concatenation (PFC) module was designed at the U-Net decoder, which fused features from different scales. Squeeze-and-Excitaton (SE) attention mechanisms were added to each layer of the PFC to filter out effective information from the feature maps. The loss function of the network is weighted based on the outputs of the PFC module at each layer, serving to supervise the feature extraction process across different layers of the network. The test results of this model on the test set are as follows: the Dice coefficient is 0.8843 and the Jaccard coefficient is 0.7926. Experimental results indicate that this model is highly robust in coronary vascular segmentation, more effectively suppressing noise under low contrast and achieving better segmentation results for coronary vessels when compared to other methods.
Magnification endoscopy with narrow-band imaging (ME-NBI) has been widely used for cancer diagnosis. However, some microstructures are rendered invisible by a white opaque substance (WOS) composed mainly of lipids. In such lesions, the morphological structure of lipids becomes another marker of tumor grade. We propose a lipid segmentation method. First, the lipid image enhancement algorithm and the specular reflection correction algorithm are introduced. Then, in the framework of the active contour model, the proposed segmentation method extracts local information from modified hue value and global information from intensity value and adaptively obtains the weight factor to segment the lipid region based on the initial contour. This method’s effectiveness is verified by a phantom experiment, which shows that it attained higher than 90% in several key measures: pixel accuracy, sensitivity, and Dice coefficient. The proposed method can accurately reflect the shape of lipids to provide available information for doctors.
The data simulation for Space Situational Awareness (SSA) can provide critical data support for the development, testing, and validation of space surveillance equipment and situational awareness algorithms (including detection, tracking, recognition, and characterization of space object), playing a significant role in building SSA capabilities. Taking the optical data simulation for space-based situational awareness as the research subject, the purpose and main research content of SSA data simulation are presented, and the typical research methods and processes of SSA optical imaging simulation are set forth. The current research status and progress in domestic and foreign related research are introduced, covering the imaging modeling and simulation achievements of different optical sensing systems such as binocular vision sensors, LiDAR, infrared sensors, visible light telescopes, and star trackers. The development trend of SSA data simulation research is analyzed, providing reference for future research ideas and approaches of SSA data simulation.
Fringe structured light technology is a non-contact measurement method, which has developed rapidly in recent years and provides a new solution for on-machine detection in mechanical processing. However, the accuracy of structured light for on-machine detection is compromised by the convoluted lighting in machining environments and metal parts’ high reflectivity, leading to inaccurate measurements. Applying high dynamic range (HDR) technology to structured light detection can reduce the effect of high reflectivity, achieving the measurement of metal parts in complex scenes. This paper introduces the measurement principle of structured light and summarizes the challenges of on-machine detection for HDR structured light. Subsequently, this paper provides a comprehensive review of HDR structured light technology. In the context of on-machine detection of mechanical processing, the HDR technology based on hardware equipment and the HDR technology based on stripe algorithm are discussed and analyzed, respectively. Following this, different technologies are summarized according to the requirements of on-machine detection. The advantages and disadvantages of various methods are presented, and the applicability of on-machine detection is compared. Finally, the potential applications are analyzed, and the technological prospects will be proposed in combination with the research hotspots of advanced manufacturing technology and precision measurement in recent years.
Laser Induced Breakdown Spectroscopy (LIBS) is a new method for qualitative and quantitative analysis of the constituents of a material using plasma spectra produced by the interaction of a strong pulsed laser with the material. In the process of pulsed laser-induced plasma, different laser parameters (energy, pulse width, wavelength), environmental conditions during the detection process and the properties of the material itself have different degrees of influence on the physical mechanism of laser-induced plasma, which in turn affects the results of LIBS quantitative analysis. We review the physical mechanisms of LIBS technology in the current state, including the basic principles of LIBS, the differences in laser parameters, and the physical mechanisms involved in the differences in environmental and material properties. It provides a basis for a deeper understanding of laser-matter interactions and for improving the detection capabilities of LIBS.
Narrow linewidth fiber lasers, based on the multi-longitudinal-mode oscillator seed source, have obvious advantages in engineering applications and space-limited loading platforms. Additionally, they are considered ideal sub-modules for high-power spectral combinations. The time domain of this type of seed is unstable due to the self-pulse effect, causing significant spectral broadening and stimulated Raman scattering effects during the amplification process, which limits their further improvement in output power and affects the purity of laser spectra. In this paper, we introduce four commonly used narrow linewidth seeds. The mechanism and suppression methods of the self-pulse effect in multi-longitudinal mode oscillator seeds are analyzed. Critical technologies essential for the optimization and relevant progress of the multi-longitudinal-mode oscillator seed source and amplifier stages are discussed in detail. A future development outlook is also presented. This paper serves as a useful reference for the design of narrow linewidth fiber lasers based on the multi-longitudinal-mode oscillator seed source.
Optical path absorption spectroscopy is an important branch of absorption spectroscopy. In recent years, there has been a proliferation of optical path absorption spectroscopy techniques based on different light source technologies, absorption cavity technologies, and detection methods. As the demands on detection sensitivity and absorption optical path length increased, optical path absorption spectroscopy techniques based on the principle of enhanced absorption emerged, including integrated cavity spectroscopy (ICOS), cavity-enhanced absorption spectroscopy (CEAS) and cavity ring-down spectroscopy (CRDS). Enhanced absorption spectroscopy is advantageous for its high spectral resolution, high sensitivity, fast response time, and portability, but it presently lacks a unified concept and clear classification criteria. This paper compares the development history of absorption spectroscopy techniques and clarifies the concept of their multi-optical path. Based on whether resonant absorption occurs in the absorption cavity, the concept of absorption spectroscopy techniques based on resonance is proposed, and the current research status of resonant absorption spectroscopy techniques is analyzed and summarized, and the applications of this technique in various fields are outlined. Finally, the future development of key technologies in resonance absorption spectroscopy is envisioned.
Optical fiber tweezers are widely used in biochemical analysis, life sciences, and other fields due to their simple structure, flexible operation, and compact size. The hetero-core structure of the optical fiber probe possesses inherent advantages in near-field evanescent wave optical trapping force, core beam coupling transmission, and cross-synergistic application of microfluidic technology, which can realize the functions of cell and subcellular particle collection and transportation, and can significantly improve the three-dimensional particle trapping capability as well as dynamic manipulation level. In this paper, the structural characteristics and application technology research progress of optical fiber tweezers based on different core structures are reviewed. This paper sorts and compares key technologies, including probe preparation, laser source, and coupling mode, in hetero-core optical fiber tweezers systems. It also summarizes and provides a perspective on the role and development of hetero-core fibers with different structures in optical fiber tweezers.
Micro-LEDs offers the benefits of high brightness, high response frequency, and low power consumption, making them an attractive candidate for future display technologies and Visible Light Communication (VLC) systems. Nonetheless, their low External Quantum Efficiency (EQE) currently impedes their scaled mass production and further applications. In order to break through the bottleneck of low EQE, we conducted an analysis of Micro-LED external quantum efficiency’s contributing factors. The influencing factors for EQE are analyzed. It is concluded that the carrier loss and non-radiative recombination caused by sidewall defects are the main reasons for the decrease in EQE. In addition, we summarized the impact of sidewall defects on carrier transport and composites, and we also reviewed the commonly used sidewall treatment technology and repair methods, and pointed out that the existing sidewall treatment methods are helpful but insufficient for improving EQE, and the mechanism of carrier interaction with sidewall defects is not very clear. It is suggested to carry out a thorough and systematic study on the types and distribution of sidewall defects, the mechanism of carrier and sidewall defects, and the defect repair mode in the sidewall treatment process. Finally, future development trends are projected. This paper offers design ideas and theoretical foundations to enhance the external quantum efficiency and accelerate the process of commercialization and mass production of Micro-LEDs.
Polarization imaging, a novel photoelectric detection technology, can simultaneously acquire the contour information and polarization features of a scene. For specific application scenarios, polarization imaging has the excellent ability to distinguish different objects and highlight their outlines. Therefore, polarization imaging has been widely applied in the fields of object detection, underwater imaging, life science, environmental monitoring, 3D imaging, etc. Polarization splitting or the filtering device is the core element in a polarization imaging system. The traditional counterpart suffers from a bulky size, poor optical performance, and being sensitive to external disturbances, and can hardly meet the requirements of a highly integrated, highly functional, and highly stable polarization imaging system. A metasurface is a two-dimensional planar photonic device whose comprising units are arranged quasi-periodically at subwavelength intervals, and can finely regulate the amplitude and phase of the light field in different polarization directions. Polarization devices based on metasurface are featured with compactness, lightweight and multi-degree freedom, offering an original solution to ultracompact polarization imaging systems. Targeted at the field of polarization imaging, this paper illustrates the functional theory, developmental process and future tendency of related metasurfaces. We discuss the challenges and prospect on the future of imaging applications and systematic integrations with metasurfaces.
In order to clarify the cavity design methods of thin-disk multi-pass amplifiers, we summarize the different types of thin-disk multi-pass amplifiers and concludes that there are four fundamental design concepts: (1) 4
Miniature head-mounted single-photon fluorescence microscopy is a breakthrough approach for neuroscience research that has emerged in recent years. It can image the neural activity of freely moving vivo animals in real time, providing an unprecedented way to access neural signals and rapidly enhancing the understanding of how the brain works. Driven by the needs of brain science research, there have been many types of miniature head-mounted single-photon fluorescence microscopes, such as high-resolution imaging, wireless recording, 3D imaging, two-region imaging and two-color imaging. In order to have a more comprehensive understanding of this new optical neuroimaging technology, we classify its technologies according to the imaging field of view, introduce the characteristics of different types of micro-head-mounted single-photon fluorescence microscopes reported so far, and focus on the optical system scheme and optical performance parameters used. The advantages and disadvantages of different schemes are analyzed and compared and the future direction of development is described to provide reference for the practical application of brain science researchers.
Non-line-of-sight (NLoS) imaging is a promising technique developed in recent years, which can reconstruct hidden scenes by analyzing the information in the intermediate surface, and "see around the corner", and has strong application value in many fields. In this paper, we review the reconstruction algorithm for NLoS imaging tasks. Firstly, considering the crossover and non-independent phenomena existing in the NLoS imaging classification, we use the different features of physical imaging models and algorithm models to reclassify them. Secondly, according to the proposed classification criteria, we respectively review the traditional and deep learning-based NLoS imaging reconstruction algorithms, summarize the state-of-the-art algorithms, and derive the implement principle. We also compare the results of deep learning-based and traditional NLoS imaging reconstruction algorithms for reconstruction tasks. Finally, the current challenges and the future development of NLoS imaging are summarized. Different types of NLoS imaging reconstruction algorithms are comprehensively analyzed in this review, which provides important support for the further development of NLoS imaging reconstruction algorithms.
Laser-Induced Thermo-Elastic Spectroscopy (LITES) is a new developed gas detection technology based on the thermoelastic effect of Quartz Tuning Forks (QTF). The QTF has the advantages of low cost, small volume, high sensitivity and wide spectral response range, and the LITES is becoming a vital method for trace gas detection. In this paper, the basic principle of gas concentration measuring based on LITES is firstly analyzed. Secondly, from the perspective of various technical methods, this paper introduces the methods for improving the sensitivity of QTF detectors, and reviews the research progress of LITES system in recent years. The performance of these systems is evaluated by the signal amplitude, Signal-to-Noise Ratio (SNR), minimum detection limit, and Normalized Noise Equivalent Absorption (NNEA) coefficient. Finally, the practical application of LITES in the field of gas detection technology is briefly reviewed, and the methods for further improving its sensitivity are summarized and prospected.
Atmospheric temperature, humidity and pressure are deemed important atmospheric parameters. Quickly and accurately understanding the temperature, humidity and pressure information of the atmosphere and their changing trends is of great significance to research on meteorology, climatology, and artificial weather research. Raman lidar can obtain various atmospheric environment-related parameters by separating Raman scattering signal inversion, which can achieve high accuracy detection of atmospheric parameter profile information. Raman lidar has unique advantages and potential in atmospheric temperature, humidity and pressure detection. With an introduction to the principle and inverse analysis algorithm of Raman lidar for atmospheric temperature, humidity and pressure detection, this paper also highlights the advantages and disadvantages along with related advances of spectral devices such as filters, etalons and gratings commonly used in Raman lidar. The detection techniques involved in Raman lidar are also included. Finally, typical applications of meteorological parameter measurements by Raman lidar are shown.
With the continuous development of optical imaging technology and the growing demand for remote sensing applications, cross-scale high-resolution optical technology has been widely used in the field of remote sensing. In order to obtain more detailed information on the target, domestic and foreign researchers have carried out relevant research in different technical directions. In this paper, through the technical classification of remote sensing imaging, we introduce a representative aerospace optical remote sensing high-resolution imaging system. It focuses on monomer structure, block expandable imaging, optical interference synthesis aperture imaging, diffraction main mirror imaging, optical synthetic aperture and other technologies. It provides a new idea for the development of high-resolution optical remote sensing loads on the ground.
With the rapid development of laser technology, the application of laser in the medical field has gained growing attention. Due to its advantages of non-contact, high precision, low damage, portability and operational flexibility, laser treatment significantly enriches the clinical treatment toolkit. Moreover, it has substituted traditional methods for certain diseases and improved the overall medical treatment capability. Currently, laser treatment has gained increasing market share and has a great potential for even more widespread applications. Here, we introduce the laser treatment technique and the requirements of medical laser systems, expound the current status of the applications of laser treatment in clinical departments in a comprehensive manner, and give suggestions regarding to the problems in the laser treatment field in China.
Periodic optical systems, such as photonic crystals and optical metamaterials, can localize high-density electromagnetic field energy at subwavelength scales and obtain extremely small mode volumes, so they have great application potential in the field of light manipulation. In recent years, a strong interaction between light and matter in periodic optical systems has been discovered, which is called Bound States in Continuum (BIC). Optics BICs are special electromagnetic eigenstates whose frequencies lie in the radiation continuum but are completely localized, and have shown interesting physics and rich application scenarios. This paper systematically reviews the classification and theory of BICs in periodic optical systems, and summarizes their basic physical properties and the latest application development. BICs in periodic optical systems are injecting new impetus into the fields of integrated optics, information optics, bio-optics, topological optics, and nonlinear optics.
Two-dimensional (2D) Bi2O2Se has attracted broad attention in the field of electronic and optoelectronic applications in the UV-Vis-NIR region due to its unique crystal structure, energy band, high carrier mobility, and excellent stability. In this paper, we review the recent research progress in the material synthesis and optical characterization of Bi2O2Se. Firstly, the synthetic method and growth mechanism of 2D Bi2O2Se are introduced, including Chemical Vapor Deposition (CVD), wet chemical process, Molecular Beam Epitaxy (MBE) and Pulsed Laser Deposition (PLD), etc. Via steady-state spectrum study, the properties change of 2D Bi2O2Se with thickness change can be studied, such as the band gap. The defect type, temperature coefficient and thermal conductivity of 2D Bi2O2Se material can be further studied by focusing on the crystal vibration mode. Transient spectrum techniques can benefit the study of relaxation process and carriers transport properties in 2D Bi2O2Se materials. Finally, we summarize the existing challenges and application prospects for the promising Bi2O2Se field.
Panoramic endoscopic imaging technology can effectively reduce the observation blind area of internal organs. It has many advantages, such as shortening the operation time, reducing the risk of intraoperative bleeding, improving the prognosis and shortening the postoperative recovery time. It has important application value in minimally invasive surgery and preoperative examination. It is a research hotspot in recent years. This paper combs the panoramic endoscopic imaging technology from two aspects: principle and product applications. Firstly, various panoramic endoscopic imaging technologies based on two-dimensional and three-dimensional imaging are reviewed, their implementation methods are described, and their key indexes and performances are analyzed. Secondly, the capsule endoscope, panoramic enteroscope and other different types of products derived from panoramic endoscopic imaging technology are compared and analyzed, and the development trend and application prospect of panoramic endoscopic imaging technology are prospected.
Besides its advantages in volume, power and beam quality, a monolithic integration Master-Oscillation Power-amplifier (MOPA) can also realize a narrower linewidth and dynamic single-mode by integrating Bragg grating. Its application value is high in the fields of frequency doubling, pumping, optical communication and sensing, which makes it a popular research topic in recent years. This paper firstly went over the mainstream structure and characteristics of monolithic integrated MOPA, including a tapered amplifier, ridge amplifier, Bragg grating and three-section MOPA. Based on their working principles and performance characteristics, we introduce the main research directions and the latest development trends in combination with their problems. Aiming at the problem of beam quality degradation at high power in monolithic integrated MOPA, the optimal design of epitaxial layer structure, facet optical film and electrode aspects are then summarized for monolithic integrated MOPAs. After that, we sort out the research progress of MOPAs with different performance characteristics for various application requirements including high power, narrow linewidth, high beam quality and high brightness. Finally, we prospect the development trend of monolithic integrated MOPA.
Rare earth-doped upconversion luminescence nanomaterials have received considerable attention from researchers due to their great potential for applications in many fields such as information security, biomedicine, optical fiber communication, digital displays, and energy. The recently-developed upconversion luminescence nanoparticles with orthogonal excitation-emission properties have attracted especially strong research interest because their distinct luminescence outputs can be dynamically modulated by switching the excitation conditions. The orthogonal luminescence properties further endow such nanocrystals with a set of new features and functionalities, which largely expands their potential applications. This review summarizes the progress in the development of orthogonal upconversion luminescence of rare earth ions, and provides a systematic discussion on design principles and construction strategies of orthogonal excitation-emission systems based on core-shell structures, as well as introduces their recent advances in various fields of applications including data storage, security anti-counterfeiting, digital displays, sensing, bioimaging and therapy. Furthermore, the prospective opportunities and challenges in the future research of orthogonal luminescence systems are also provided.
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Supervisor: Chinese Academy of Sciences
Sponsors: the Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP), CAS
Editor-in-Chief: Wang Jiaqi, Academician
ISSN 2097-1842
CN 22-1431/O4
CODEN ZGHUC8
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