Outdoor experiments of down-looking inverse synthetic aperture imaging lidar at 1.8 km and 3.4 km are processed. A nonlinear correction algorithm is given under the remote imaging mode, in which the phase delay cannot be neglected. In the experiment, the targets are pyramids put in the unmanned aerial vehicles and the unmanned aerial vehicles with retro-reflective material. The images of pyramids in different imaging distances and the unmanned aerial vehicles at 1.8 km are obtained through the range bin alignment algorithm in the orthogonal direction and phase compensation algorithm in the azimuthal direction. The two-dimensional resolutions reach 7.2 mm×5.8 mm at 1.8 km and 12.7 mm×9.2 mm at 3.4 km.

In order to achieve the quantitative analysis of infrared filters’ radiation characteristics, we propose an equivalent emissivity inversion method for infrared filters in the cutoff band and establish the basic mathematical model of the inversion method. Firstly, in two cases, whether placing the infrared filter in the light path or not, we conduct the radiometric calibration for infrared imaging system and then calculate the self-radiation which is caused by infrared filter in the cutoff band based on the calibration results. Secondly, based on the mathematical model of radiation from the limited surface source to the micro surface source in polar coordinates, we inverse the equivalent emissivity of the infrared filter in the cutoff band. According to the basic mathematical model, we carry out an inversion experiment of a mid-wave infrared (MWIR) filter, in two cases that the integration times are set to 0.8 ms and 4.0 ms. The result of the equivalent emissivity, arithmetic average of inversion values obtained in the two cases, is approximately equal to 0.420, so that the equivalent reflectance is approximately equal to 0.580. The relative difference value of the two experiment cases is small, approximately equal to 1.9%. We conduct the reflection imaging experiment of the MWIR filter. It is proved that the MWIR filter has strong reflective ability of radiation in the cutoff band. What’s more, the conclusion of the inversion experiment is verified qualitatively by the phenomena of the reflection imaging experiment.

Due to the absorption and scattering effects of light in water, propagation characteristics of lasers underwater become complicated. In particular, the backscatter causes the target contrast to decrease, which makes the use of lasers in underwater detection face a great challenge. Carrier modulation technique can be used to suppress the backscatter for underwater lidar. Computer simulation based on Monte Carlo method is used to establish an underwater detection model for photons of Gaussian pulse lasers modulated by cosine signal. The effects of parameters such as pulse width, modulation frequency, and modulation depth on detection results are discussed. The results show that, compared with traditional pulse lidar simulation results, carrier modulation technique with correlation detection can effectively improve the underwater target contrast. The pulse width has the optimum range. The modulation frequency has effect on the signal-to-noise ratio and ranging accuracy of the target echo signal. The greater the modulation depth, the higher the signal-to-noise ratio of the target echo signal.

Based on the demand of site selection for large infrared telescopes, an infrared radiation measurement device is developed to measure the M' band (4.605-4.755 μm) atmospheric infrared radiance and extinction characteristics at Lijiang and Chengjiang observatories. The data of temporal and spatial variations of atmospheric radiation is analyzed by Allan variance method and atmospheric radiative transfer equation, and the influence of temporal-spatial variation of radiation on infrared astronomical observation is discussed. The results show that the radiative fluctuation in the low frequency region is large, Allan variance increases exponentially with integration time, and the fitting parameters of Allan variance for Lijiang and Chengjiang observatories are 0.794 and 1.238, respectively. From zenith to 60° zenith angle, radiance of Lijiang and Chengjiang observatories increases by 68% and 72%, and the transmittance decreases to 0.46 and 0.52, respectively. Infrared astronomical observation needs chopping, and the best chopping frequencies at Lijiang observatory of the single pixel, 2×2 Binning and 4×4 Binning modes are 0.030, 0.070, 0.144 Hz, respectively. Allan variance, atmospheric extinction, and the best chopping frequency can be used to guide the site selection and design of large infrared telescopes.

Side-scattering lidar based on CCD, which is not affected by geometrical factors, is a powerful tool for ground layer aerosol detection. The detection technology at night is mature. Since moonlight and starlight in the background light are much weaker than the sunlight, the signal-to-noise ratio is very low when we detect ground layer aerosol during daytime using the detection technology used at night. In experiments, lens with a small field of view and a narrowband filter is selected. Meanwhile, correcting narrowband filter transmittance, reducing single exposure time, and multi-average-exposure are applied to improve signal-to-noise ratio effectively. The daytime case shows that the aerosol backscattering coefficient profile from side-scattering lidar is consistent with that from backscattering lidar in the range from 0.75 km to 1.5 km. The correctness of side-scattering lidar detection under 0.75 km is also verified. Continuous 37 h profiles of aerosol backscattering coefficient of Hefei near ground region are calculated, and the analysis combined with temperature and PM2.5 mass concentration is conduct. The results indicate that the improved side-scattering lidar detection technology is correct and feasible.

One phase retrieval method based on the Talbot effect of Ronchi grating is proposed. A CCD camera is placed at the Talbot distance of Ronchi grating to record the self-image intensity distribution of Ronchi grating. By using the stochastic parallel gradient descent (SPGD) algorithm, the coefficients of Zernike polynomials are optimized to retrieve the input phase. The numerical simulation results show that, the proposed method can quickly achieve a high-precision phase retrieval and possesses the advantages of fast convergence, high precision, and anti-noise and so on.

An improved blind phase noise compensation algorithm, two-stage projection histogram (PH) algorithm, is proposed. Firstly, we use a series of uniformly distributed test phases to rotate the phase of the received signal, and project the received signal onto the real axis to obtain the projected histogram; secondly, we count the number of constellation points near the projection center and take the test phase with the largest number as the coarse phase shift value; thirdly, we consider coarse phase shift value as the center, take a certain number of test phases uniformly, repeat the estimation steps of the one-stage PH, and obtain the accurate phase shift value for phase compensation. The performance of the proposed algorithm is experimentally verified in the coherent optical orthogonal frequency division multiplexing passive optical network (CO-OFDM-PON) system based on optical comb. The results show that the proposed algorithm has a good compensation effect on the common phase noise of 10×8 Gbit/s CO-OFDM system, and the bit error rate (BER) is reduced by at least two orders of magnitude. Compared with the one-stage PH algorithm, the proposed algorithm need only 1/4 number of test phases, which greatly reduces the complexity of the system and can be used to common phase noise compensation for CO-OFDM systems.

Previous studies show that intrachannel nonlinear effects are the dominate factor which limits the performance of high-speed long-haul quasi-linear dispersion compensated fiber-optic transmission systems. In this paper, we compare the performance of different chromatic dispersion compensation schemes like pre-, post-, and symmetrical-dispersion compensations in detail by numerically solving the coupled nonlinear Schr dinger equations in the presence of intrachannel four-wave mixing (IFWM) in quasi-linear transmission systems. It is found that IFWM is the dominant limiting factor for a typical dispersion compensated quasi-linear transmission system. For a fixed Er-doped optical fiber amplifier spacing, optimal compensation scheme depends on transmission bit rate. As bit rate increases, the performance of pre-compensation becomes better and better. On the contrary, post-compensation exhibits its advantage more and more as bit rate decreases.

With the continuous development of the research in visible light communication system, it is highlight to solve the problem of lacking uplink communication. The bi-directional visible light communication system means that both ends of the system need to realize photoelectric conversion and electro-optical conversion at the same time. In this paper, we propose a real-time bi-directional visible-light communication system scheme with light-emitting diodes (LEDs) as both optical signal transmitter and receiver, in which we design the mechanism of controlling LED bi-directional work by the way of time-division multiplexing to achieve a bi-directional visible light communication. The real-time bi-directional communication system experiments are done under the different elevation angles of transmitter and receiver. The results show that the system scheme can realize real-time bi-directional visible light communication at a distance of more than 2 m and a transmission rate of 8 Mb/s only with LED as optical transmitter and receiver, without strict alignment and relaying amplification.

Optical antenna for indoor visible light communication has such problems as small field of view, non-uniformity of the irradiance distribution at the receiver, and low received power under the low power light source condition. We design a planar concentrator as an optical antenna and establish a gain theory. We establish a visible light communication system model based on planar concentrators in a 5 m×5 m×3 m room, which use a planar concentrator with a field of view of 50° as an optical antenna. The simulation results show that the received average powers after using the concentrator in the direct link channel and the non-direct link channel are increased by 16.2411 dBm and 16.4956 dBm compared with that under the direct detection.

Extrinsic fiber Fabry-Perot (F-P) sensor could detect partial discharge in liquid-solid composite insulation, but natural frequency and sensitivity of F-P sensor are affected by viscous damping and added mass of liquid insulation. We use finite element analysis method to simulate the amplitude-frequency response characteristics of F-P sensor under forced vibration in air and liquid insulation medium, and analyze the amplitude-frequency characteristics and sensitivity of F-P sensor at different temperatures. We propose the F-P sensor with isolating liquid insulation structure to eliminate the effect of medium and design an experiment system to measure amplitude-frequency response curves of F-P sensors at different temperatures. The experimental results show that due to viscous damping and added mass of liquid, natural frequency of F-P sensor in liquid insulation transformer oil is 0.58 times of that in air, the bandwidth of amplitude-frequency curve becomes wider, and the harmonic response amplitude decreases. Furthermore, the temperature of liquid medium increases, the natural frequency of F-P sensor increases, the bandwidth of amplitude-frequency becomes narrower, and the harmonic response amplitude and sensitivity increase. It’s found that F-P sensor with isolating liquid insulation structure are immune to media viscous damping and additional mass.

A novel microstructured optical fiber is proposed and can support the transmission of 22 orbital angular momentum (OAM) modes, which has the advantages of flat and low dispersion and low loss. The OAM modes can be well-separated due to the large effective refractive index difference (above 10-4) between the eigenmodes corresponding to each OAM mode. In the range of 1500-1600 nm, By adjusting the diameters of the first two inner rings of air-holes, we can controll the dispersion of each mode in the range from 0 to 50 ps·(nm·km)-1. The dispersion variations of HE71 and EH51 modes are less than 12.8 ps·(nm·km)-1, and the dispersion variations of other modes are less than 5 ps·(nm·km)-1. Moreover, this fiber possesses a very low confinement loss below 1.35×10-9 dB/m for all the supported modes at 1550 nm.

Aiming at problem that the single image clearness algorithm cannot guarantee the effect of noise and fog reduction, a new algorithm for foggy and noisy single image clearness using the lazy random walk model is proposed. Firstly, physical meaning of existing atmospheric scattering model is analyzed and improved to be made more consistent with the specialist of the actual foggy images. Lazy random walk model is used to estimate the attenuation term of improved haze degeneration model. Secondly, geometric constraint and color-line prior are used to obtain accurate atmospheric light of the degeneration model. Fog-free images with little noise are recovered at last. Experimental results show that the proposed algorithm can obtain the best defogging effect and restrain the noise, and it has strong robustness.

Based on the dark channel prior, we propose a dehazing algorithm for single image, discuss the adjustable parameters of the algorithm, and analyze the impact of parameter variation on the final dehazing results. In the primal algorithm, the sky area is mentioned as no need of special handling. However, we find that this area needs to be treated separately. We set threshold to isolate the sky area separately and receive better effect. Meanwhile, we study on the introduced guided-filter, and analyze the impact of parameters on the real-time performance of the algorithm. In order to improve the real-time performance of the algorithm, we reduce the picture firstly in order to shorten the calculation time, and then enlarge the image by image interpolation method to get haze-free image. The experimental results show that the operation time of the algorithm can be reduced by 85.7% with the premise of image haze removal.

In order to improve the visual quality of low-dose computed tomography (CT) images, an image denoising method based on convolutional neural network is proposed. The batch normalization is introduced to the network, and the mapping function between low-dose CT images and their corresponding noise images is learned. The dilated convolution is used to expand the receptive field without increasing the complexity. Besides, the feature maps from the front and back layers are concatenated, and all the feature maps of convolution layers ahead can be used as the input of a subsequent convolution layer.It encourages the reuse of feature maps in the network. The experimental results show that the proposed network architecture achieves better denoising performance and sharply reduces the network complexity when compared with the state-of-the-art method at present. So, it can quickly and significantly improve the visual quality of low-dose CT images.

During image super-resolution reconstruction for multi-dictionary learning, common methods such as K-means clustering, Gauss mixed model clustering and so on can lead to poor quality and instability of image reconstruction. To solve the problem, we propose a novel image super-resolution reconstruction algorithm based on hierarchical clustering. Firstly, features are extracted from sample image blocks, and hierarchical clustering is performed, then K dictionaries are trained with improved principal component analysis method. Secondly, the test images are cut into a number of image blocks, and the most suitable dictionary is adaptively matched to reconstruct the image block. Finally, the whole image is optimized to achieve global reconstruction. The results show that the proposed algorithm in this paper has high feasibility, and can effectively improve the reconstruction quality of image. Compared with peak signal-to-noise ratio and structural similarity of the images reconstructed by the traditional algorithms, those of the images reconstructed by the proposed algorithm increase.

As an analytical camera pose estimation algorithm, EPnP algorithm has attracted much attention in recent years for its low computational complexity. However, it is not robust to image noise. Hence, an iterative version of EPnP algorithm, called IEPnP, is proposed. The primary ideas of EPnP are preserved in IEPnP, 4 virtual control points are introduced, and their coordinates in the camera coordinate system are obtained through an initialization process based on weak perspective projection model. Gaussian-Newton algorithm is applied to optimize the coordinates of the virtual control points in the camera coordinate system. Finally, the pose estimation result is acquired by solving an absolute orientation problem. Meanwhile, the computational process is simplified in IEPnP. Simulations under different image noise levels are implemented, and the results show that IEPnP is more robust than EPnP to image noise while maintaining a high computational efficiency.

We study the theory of laser reflective tomography technology based on computed tomography. In practice, due to the movement of the target and the vibration of detection platform, there are the shifts between the reflection projections of non-cooperated target at different angles and the target rotation center, which is projection-misalignment and causes the distortion and constructed defects of reconstructed image from projections. We use the error-reduction and hybrid in-out algorithm to recover the phases of reflective tomography reconstructed images with misaligns. The simulation verifies the feasibility of the algorithm under the angles of oversampling, full projection, and sparse projection of projection angles.

The light field camera can capture direction and intensity of light rays at the same time, when setting a lenslet array at a specific position between the primary mirror group and the sensor. We propose an image digital watermarking method for four-dimensional light field image obtained by the light field camera in the frequency domain. In this method, the embedded information is compiled by Base64 to generate a two-dimensional image, and then a virtual computational light field matching the original light field coordinates is established based on the image scrambled by Aronld cat map. A slice of frequency domain is obtained from virtual computational light field after the four-dimensional Fourier transform. By means of slice substitution, the information is embedded into original light field, in order to realize the aim of encrypting light field image. Finally, the watermark information is extracted successfully, by means of the Fourier inverse transformation and image binarization. A light field acquisition system is built, and a light field image is encrypted by the proposed method. The experimental results show that the encrypted light field has a high signal-to-noise ratio and strong correlation with the original light field. The proposed method is simple, fast, and reliable. There is no obvious artifact and distortion in the encrypted light field image.

Compared to the traditional synchronous parallel computing, an asynchronous parallel alternating direction method (ADM) for total variation (TV) minimization reconstruction, namely asynchronous alternating direction total variation minimization method (Async-ADTVM), is proposed in this paper. Under the asynchronous parallel computing framework, Async-ADTVM transforms TV minimization reconstruction model to the problem of fixed-point iteration, which is solved by asynchronous parallel ADM. It is implemented on the graphics processing unit (GPU) cluster based on message passing interface technology. Experimental results show that the proposed Async-ADTVM can provide a little higher calculation accuracy than ADTVM. Meanwhile, it can provide a higher speed-up ratio than the traditional multi-GPU acceleration strategy when the performance of each GPU is different.

Optical synthetic aperture (OSA) can greatly improve the spatial resolution of the optical system. However, due to the aperture dispersion and sparsity, the intermediate frequency (IF) modulation transfer function (MTF) of OSA imaging system is significantly lower than that of single aperture system. We first analyze the imaging method and principle of OSA imaging system, then discuss the reason and principle of the IF MTF reduction of OSA. Taking the filling factor as a clue, we propose the method of processing the IF MTF reduction with large filling factor and the IF MTF missing with small filling factor. For the IF MTF reduction, we use image restoration method to restore the IF information in the image. For the IF MTF missing, we fuse two images generated in two systems respectively to compensate the IF information. We analyze the feasibilities of the two methods and simulate the two cases in Zemax software. The results show that both methods are feasible.

High dynamic range imaging technology is a research hotspot in the field of optical imaging. Digital microscopy device (DMD) has the characteristics of modulation incident ray spatial information. A high dynamic range imaging system with high-resolution is developed based on DMD, which could improve the dynamic range of the imaging system. At the same time, in order to reasonably and effectively control the DMD, the response curve of DMD modulation and CMOS image detector are calibrated by using mathematical analysis method, and the response curve calibration method of DMD camera is proposed according to the structure and imaging characteristics of the imaging system. The experimental results show that the imaging system has a dynamic range larger than the ordinary ones, which can reach more than 96 dB. The fast response function calibration of the DMD camera is also completed, which provides the powerful foundation for the adaptive adjustment of the DMD mask.

Traditional biometric system stores the biometric template in the database directly. While the biometric template is unique and permanent, it can’t be used anymore if stolen. To solve this problem, we propose a palm vein recognition algorithm with pseudo image storage, which doesn’t input any key information and doesn’t store original palm vein template. In the stage of register, the system collects palm vein images under near-infrared light. Then the collected image is stored in the form of pseudo image. In the stage of recognition, the pseudo image is decrypted and the feature is extracted. The feature is matched with input image and the authentication result is given. The proposed algorithm is tested on PolyU database, CASIA database, and self-built database. The experimental results show that in sample range of 300, the proposed algorithm can reach the equal error rates of 0.4135%, 0.5576%, and 0.4744% and recognition times of 325.0740 ms, 316.0800 ms, and 322.6530 ms for the above databases. The algorithm has practical value for security and checking-in occasions in certain sample range.

With the exposure time of 0.205 ms, the relationship between the object observation speed and the speckle contrast when the observable speed range includes a decorrelation area and a non-decorrelation area is investigated. The results indicate that, based on the variance trend of contrast with sampling frame and the correlation coefficient curve of time sequence speckle image, one can distinguish the speed difference between these two areas under complicated environment. Meanwhile, by choosing the suitable number of speckle image frames, one can provide a higher sensitivity for detecting the speed variance in the small speed range and the large speed range.

In order to solve the problem that traditional Chan-Vese (CV) model is difficult to extract metallographic grains quickly and accurately, the metallographic image segmentation method based on improved CV model integrated with local fitting term is proposed. We use the reciprocal cross entropy threshold segmentation rule to replace the regional term of the energy function in the traditional CV model and construct a new level set model. The proposed model can minimize the reciprocal cross entropy between original and segmented image, and accurately segment the metallographic images with more noises and larger local gray scale. In addition, Taking that the reciprocal cross entropy will increase algorithm’s computational complexity into account, the maximum absolute median difference is adopted to adjust energy weight inside and outside the curve to accelerate curve evolution. The distance regularized term is introduced to avoid initialing level set function, and accelerate the model convergence. Experimental results show that comparing with other traditional CV models, the proposed model has obvious advantages both in segmentation result and efficiency.

Combined radiation calibration method based on infrared calibration stars and internal blackbody calibration source can improve the accuracy of infrared radiation measurement of spatial object. The blackbody calibration source is located inside the infrared radiation measurement system, which is used to calibrate the responsivity of the optical system. According to the atmospheric extinction model, using astronomical aperture metering method, the atmospheric extinction and system transmittance coefficient are obtained by observing multiple infrared calibration stars with higher spectral resolution at different elevation angles. The experimental results of the verification test of 700 mm aperture ground-based medium wave infrared radiation measurement system show that, in the case of sufficient exposure of star image, the inversion error of the star irradiance of the combined radiation calibration method is better than 11%. The combined radiation calibration method is simple and low cost, which can be used to calibrate the measurement equipment on-site at any time.

Errors causesd by radial phase-shifting nonuniformity of test optics are different when using different steps of phase-shifting algorithms to process interference fringes. Here, a error analysis model is established based on optical principle of point diffraction interferometery. Take 5, 6, 7 and 13 step phase-shifting algorithms as example, phase-shifting errors which are directly caused by radial phase-shifting nonuniformity are first analyzed, and then be introduced into the interferometry model. The influence of this phase-shifting error to final optical surface testing results are analyzed later and a new polynomial error correction method based on error preestimate is proposed. The analysis results show that the more the phase-shifting steps are, the larger the figure error caused by radial phase-shifting nonuniformity is. Each of these figure error shows a paraboloid like distribution. Also, removing the defocus item from Zernike polynomial of final optical surface testing results is equal to have had a quadratic polynomial correction of this error. If the numerical aperture of test optics are no more than 0.3, the error caused by radial phase-shifting nonuniformity can be ignored after the quadratic polynomial correction.

According to the requirement of target range test of photoelectric sights at present stage, aiming at the defects of non-quantitative, large error and low efficiency of traditional parallax detection methods, a parallax detection method based on sine-like micrometric method is proposed. Quick and quantitative test of photoelectric sight parallax can be realized by the proposed method. Taking the fast-observing principle of the traditional pendulum method, sine-like micrometric method is used to realize the quantitative data acquisition, and an improved parallax detecting device with sine-like micromotion subdivision mechanism is constructed. Three kinds of typical optoelectronic sights samples are selected, and the test effect comparison experiments of four kinds of parallax test methods are conducted in detail. The results show that the parallax detection method and device based on sine-like micrometric method can not only ensure the testing accuracy of 0.01',but also meet the requirement of high efficiency and high precision in the target range test of photoelectric sights, and the test result is superior to other traditional parallax detection methods.

A phase unwrapping method for phase-type optical fiber sensors and large-scale phase measurement is proposed, which combines the phase demodulation of 3×3 fiber coupler and the dual-wavelength phase measurement method in digital holography. The unwrapped phase of the synthesized wavelength is used to compensate the wrapped phase of the single wavelength. And the wide-range, error-free phase change information is obtained. The optical fiber Michelson interferometry system based on dual-wavelength of 1310 nm and 1550 nm is established. The large range vibration generated by the piezoelectric displacement platform is measured. And the feasibility and validity of this method are verified. Compared with the phase demodulated result of the 1310 nm single wavelength, the proposed method can make the measured optical path difference expand to 6.5 times.

In order to reduce the phase error caused by the nonlinear response of digital projectors in three-dimensional measurement system of grating projection, a multi-frequency fringe inverse-phase error compensation method is proposed for improving the accuracy and speed of the object phase measurement. By projecting the compensated phase-shifted fringe pattern with the same maximum phase frequency and the same phase shift, the two phased phase diagrams with the same phase error and opposite signs are obtained. After the operation, their errors are canceled and compared with the multi-frequency method to get the exact absolute phase value. A standard plane is used for verifying the proposed method, the comparisons are done with recently proposed Hilbert transform compensation method and classical phase compensation method. The experiments results show that the proposed method can improve the accuracy and speed of phase measurement effectively. The feasibility and validity of the proposed method is verified by phase error compensation for a free form surface and object of discontinuous surface.

By using the six temperature model theory on the kinetic process in a CO2 laser system, we build a mathematical model to calculate output characteristics of Q-switched CO2 laser power amplifier. Theoretical analysis as well as numerical calculation is carried out, and the effects of parameters such as beam split ratio on output pulse characteristics and output spectra are discussed. The results show that the Q-switched CO2 laser power amplifier has a critical gain length and a critical beam split ratio, below which no laser output can be obtained. The laser pulse waveform, peak power, pulse width, and output spectra of the Q-switched CO2 laser power amplifier are all effected by the beam split ratio and pumping electron density. The less the beam split ratio, the greater the output Q-switched laser pulse width, and the lower the laser peak power. The Q-switched CO2 laser power amplifier utilizes the high gain characteristic of Q modulation. By controlling the low power branch of Q-switched elements, we realize the Q-switched pulse CO2 laser output with high average power. The problem that Q-switched CO2 laser power amplifier is difficult to operate at high power is well solved.

The terahertz quantum cascade laser (THz QCL) has a wide gain spectrum, and the emission is often multiple-longitudinal mode when using the conventional Fabry-Perot cavity. A second-order distributed feedback THz QCL can eliminate the mode degeneracy to realize the single longitudinal mode lasing by means of surface radiation loss. Based on the coupled-mode theory, the computational formulas of the basic parameters for the second-order distributed feedback THz QCL with the single-side metal waveguide are deduced. The influences of the grating structure parameters on the coupling coefficients, threshold gain, photon density, and external differential quantum efficiency is investigated. When the grating with a duty cycle of about 0.15 and a depth in the active region of 0.5 μm is etched on the waveguide with a natural cleavage plane, the threshold gain is low, the photon density distribution within the cavity is uniform, and the single longitudinal mode emission can be achieved.

Spatial narrow linewidth laser, as the local oscillation of the spatial strontium atomic clock, determines the short- and medium-term stability of the space strontium atomic clock. Due to the limited load resources of the space station, the optical system of spatial narrow linewidth laser not only meets the functional requirements of the space light clock reference transition, but also considers the factors of volume and weight. In addition, the space narrow linewidth laser system has strict requirements on the power and heat consumptions. Improving the optical power utilization efficiency under the condition that the output optical power of the laser source is constant is the key to ensure the follow-up optical path power demand. In order to reduce the volume and the weight of the system, we build the optical path of the system with the miniaturized optical components. To improve the utilization ratio of the optical power of the system, we build the experimental platform of the optical functional unit on the basis of the short focal two-lens scheme. The result shows that the single-pass diffraction efficiency of the acousto-optic modulator is greater than 90%, and the double-pass diffraction efficiency is greater than 70%. We scan the acousto-optic modulator drive signal. It is found that the optical fiber coupling efficiency changes by 50% within ±20 MHz scanning range, which satisfies the space and power application requirements.

A new method for fast calculation of low dynamic carrier velocity based on improved singular value decomposition (SVD)-Harris is proposed to solve the problem that the poor real-time performance of low dynamic carrier velocity calculation under the indoor environment with uneven illumination. Firstly, we use the SVD to compress and reconstruct the two adjacent visual images and use the improved Harris corner detection algorithm to detect the feature points of the two frames. Secondly, we use the normalized cross correlation (NCC) template matching algorithm to roughly match the feature points of two adjacent visual images. Thirdly, we use random sampling consistency (RANSAC) algorithm to eliminate the false matching point pairs. Finally, we use the information of the feature matching point pairs to calculate the carrier velocity. The experimental results show that the average calculation time of the traditional algorithm is 3.07 s, while that of the improved algorithm is 0.71 s. The error matching rate of the traditional algorithm is much greater than that of the improved algorithm. Compared with the traditional NCC template matching method, the proposed algorithm not only guarantees the accuracy of the velocity calculation of the low dynamic carrier, but also greatly improves the calculation efficiency of the carrier velocity under the indoor environment with uneven illumination. This study provides a theoretical basis for realizing the real-time visual navigation of indoor mobile robot.

Binocular vision is a classical and efficient method in machine vision. Aiming at the problem that it is difficult to extract feature points of smooth surfaces without chromatic aberration, we propose a method of creating color features on surfaces with uniform laser grids, and a feature point extraction and matching algorithm. Firstly, in order to extract the laser grid line, the laser line breakpoint is spliced and transformed into a single pixel connected line by the expansion and corrosion algorithm. Then, the feature points are extracted by the connectivity of eight neighborhood and four neighborhood of points on the connected line. Finally, the extracted feature points are numbered according to the location information to complete the matching of feature points. The experimental results show that the algorithm has good robustness, high extraction accuracy, high matching accuracy and high repetition rate. The distance error between the feature points after three-dimensional reconstruction is less than 0.05 mm, and the standard deviation is 0.0362 mm. The proposed algorithm can carry out feature point extraction and matching directly, which is more accurate than the method of discrete feature lines as feature points. It can be applied to the uniform sampling detection of points on surfaces.

Microring resonator is a key component in integrated optics, and its filtering characteristics in application are affected by the input optical power. However, the steady model of microring resonator only includes the linear optical effects for a long time. In this paper, a new steady model of microring resonator is deduced. The loss and phase shift in the feedback waveguide of the microring resonator and the modification of coupling ratio in the microring coupler induced by optical nonlinear effects are taking into account, and following nonlinear optical effects in silicon waveguide are included: self-phase modulation, two photon absorption and thermal-optical effect. Then the influences of two photon absorption and the modification of coupling ratio in the coupler induced by the optical nonlinearity on the depth of notch filter are emphatically discussed. Simulation results show that when the thermal-optical effect and the self-phase modulation generate the frequency shift of the resonance spectrum, the change of the coupling ratio of the power dependent coupler has a great influence on the notch filter depth of the microring resonator.

The technology of monocentric multiscale imaging provides an effective approach to overcome the contradiction between resolution and field of view in traditional optical imaging. In this paper, the model of monocentric multiscale imaging is applied in the airborne optoelectronic detection system to achieve the wide field of view and high-resolution detection of the target. We comprehensively analyze the characteristics about the space distribution and transmission of the target radiation, and the imaging performance of optical system. Then we establish the theoretical model of detection capability of the monocentric multiscale imaging system to obtain the variation relationship between the detection capability of the system and the parameters such as the aperture, focal length, and distance of the element lens. The actual optical system is designed by using the optical design software Zemax, and the response characteristics of the signal to noise ratio (SNR) of the spectral signal of the incoming moving target is numerically simulated. The results show that appropriately increasing the focal length of the objective lens, reducing the focal length of the eyepiece, increasing the aperture of the system and reducing the detection SNR threshold of the monocentric multiscale imaging system can effectively improve the detection capability of the imaging system.

According to the non-imaging optics theory, a freeform surface design method based on collimation system is proposed. With the geometrical optics as the theoretical foundation, a new type of light-emitting diode (LED) collimation system is designed based on the rotational symmetry of the central axis. The light collecting angle of the collimating system is about 236°, and the semi-luminous angle of the emitted light is less than 1°.Based on geometrical optics and the law of energy conservation, a freeform surface is designed on the exit plane of the collimating system. The ‘many-to-one’ topological relation of energy and the illumination design method of uniform rectangular spot are presented. The surface data of freeform surface is solved by Matlab software. The model of this surface is built on the basis of non-uniform rational B-splines (NURBS) surface theory by SolidWorks software. Simulation analysis is carried out by LightTools software of optical design. The simulation results show that the new collimating system can collimate the light of large angle, and the design method of the freeform surface based on the collimating system can achieve uniform light spot of rectangle.

A novel and compact terahertz (THz) polarization beam splitter based on photonic crystal is proposed. Transmission without diffraction of transverse electric (TE) and transverse magnetic (TM) modes is realized by using the self-collimating effect, while the separation of TE and TM modes is realized by using the band gap characteristic. The characteristics of the terahertz polarization beam splitter is simulated and analyzed by using plane wave expansion method and time domain finite difference method. The results show that the polarization beam splitter can realize polarization separation in the frequency range of 2.9-3.01 THz. While the frequency is 3 THz, the reflectivity of TE mode and the transmittance of TM mode are both higher than 90%. The extinction ratios of TE and TM modes are 19.9 dB and 26.24 dB, respectively. Moreover, compared with the previous photonic crystal terahertz polarization beam splitters, the proposed polarization beam splitter is simpler to design, easier to realize (without defects), smaller in size (650 μm×650 μm) and wider in bandwidth (2.9-3.01 THz).

This paper proposes a dimming calculation model for red/green/blue/warm-white (R/G/B/WW) light emitting diode (LED) based on four channels’ pulse width modulation (PWM). According to the characteristics of two-channel and three-channel PWM, the proposed model adopts Chebyshev method of black body locus to determine the relationship between chromaticity coordinate and correlated color temperature(CCT) of the synthesized light. When the color rendering performance is optimized, the functional relationships between chromaticity coordinate and duty cycles, CCT and duty cycles of the mixed light are established. And the experimental verification is carried out with R/B/G/WW LED. The experimental results show that R/G/B/WW LED module can realize a wide range of CCT tunable white light from 2900 K to 7600 K. When the luminous flux is set to 300 lm, the maximum relative error of CCT is 0.99%, and the maximum relative error of color rendering index (CRI) of the mixed light is 0.11%. When the luminous flux changes in the range of [150,800], the maximum relative error is 2.02%. The model can be applied to LED dimming of four channels. And its calculation method is simple, the dimming precision is high, and the hardware is easy to implement.

A polarization phase-shifting interferometric method is proposed to measure the central stress in flat glass based on the principle of plane polarization interferometry. Rotating analyzer can be used to realize polarization phase-shifting. The stress birefringence values and their distribution curves are obtained with the constructed mathematical model, and then the central stress value can be calculated from the stress-optical coefficients. The central stress of float flat glass is experimentally investigated and the experimental results show that the measurement error of this proposed method is less than 3%, and the measurement repeatability is superior to 1 nm·cm-1, which can verify the feasibility of this proposed method.

The key technique of azimuth measurement system based on magneto-optical modulation is magneto-optical modulation technique, in which the accurate expression of the internal axial magnetic field of solenoid modulated by alternating current is important, however there is little study on effect of magnetic material's parameter characteristic in magnetic field. Take the magneto-optical material TGG crystal as an example, we study the influence of TGG dielectric constant change on the axial alternating magnetic field of the solenoid. Firstly, we assume that the dielectric constant of magneto-optical material in solenoid is a constant, the model of internal axial magnetic field of solenoid modulated by sine wave signal is established with the Maxwell's equations. Secondly, according to the molecular formula of TGG, the variation function of TGG dielectric constant with modulation signal frequency is acquired by VASP software. At last, the variation function is introduced into the established magnetic field model, and the effect of TGG dielectric constant on the internal axial magnetic field of solenoid modulated by sine wave signal is got. The results shows that when the modulation signal frequency rises, the TGG dielectric constant reduces, which slows the amplitude attenuation trend of internal axial magnetic field of solenoid, and advances the rapid attenuation stage in the magnetic field phase shift attenuation process, and speeds up the attenuation velocity of the rapid attenuation stage. The research method provides a reference for studying the effect of magneto-optical material on internal axial magnetic field of solenoid, and measurement precision of azimuth misalignment angle.

The interaction between a coherent state light field with time-varying frequency and two-level atoms is investigated under non-rotating-wave approximation. The time evolution of the atomic population inversion is discussed when the field frequency changes with time in a sine or a square wave way. The numerical results indicate that, when the light field frequency does not change with time, the period of atomic population inversion increases with the increase of the mean photon number. When the field frequency changes with time in a sine wave way, the collapse-revival period and the amplitude of atomic population inversion are strongly affected, and the frequency of the light field plays a modulation role in the oscillation frequency of evolution curves. When the field frequency changes with time in a square wave way, the collapse-revival period of the atomic population inversion changes and a new collapse-revival phenomenon emerges.

Einstein-Podolsky-Rosen (EPR) steering shows an intermediate type of quantum nonlocality which is distinct from both quantum entanglement and Bell’s nonlocality, especially, one-way EPR steering has a significant influence on the secure quantum secret sharing. A scheme to effectively change the characteristic of EPR steering, which is implemented by adding noise to one part of an EPR state, is presented. With the introduction of the noise, the relationships between the steering parameters and the reflectivity of variable beam splitter are analyzed, and the change process of the EPR steering direction from two way to one way is investigated. This study is of great importance in the asymmetric quantum nonlocality control and the quantum control in the process of quantum information transmission.

Aiming at the problem of feature redundancy in polarimetric synthetic aperture radar (SAR) application, a semi-supervised dimension reduction algorithm: semi-supervised local discriminant analysis (SLDA) is proposed by combining the thoughts of linear discriminant analysis (LDA) and locally linear embedding (LLE). Firstly, the regularization term is established based on local preserving property of LLE to avoid overfitting problem during learning. Then, discriminant analysis with regularization is performed on labeled data set in order to improve the generalization ability and preserve the local geometric structure in original space for the whole data. Dimension reduction experiments are performed on all polarimetric SAR data from Flevoland regions obtained by RADARSAT-2 and AIRSAR satellites. The results show that the low dimensional features extracted by SLDA has the characteristics of “intra compactness and inter separation”. Further classification experiment results show that SLDA can make the classification accuracy reach about 90% only with 1‰-2‰ labeled samples, and the classification performance of SLDA is superior to other comparison algorithms.

The singular value decomposition method is used to study the characteristics of light energy coefficient matrix of a laser particle size analyzer, and the sensitivity parameters are defined to express the variance of particle size distribution with the light energy distribution. The measurement upper limit under certain parameters is obtained. An analytic formula which discloses the relationship between the measurement upper limit and the physical parameters is derived, which shows that the measurement upper limit of the instrument is determined by the minimum acceptance angle of this instrument for the scattered light under the condition of constant incident wavelength. The experimental results verify the correctness of this formula.

Acquiring the concentration of bacteria in water quickly and accurately is of great significance for the supervision hygiene and safety of drinking water. We use multi-wavelength transmission spectroscopy to determine the concentration of bacteria in water, and mainly study the influences of different normalizations of the spectra (particle concentration normalization, maximum normalization, integral normalization, and average normalization) on the accuracy of bacterial concentration. According to the spectra interpretation model of Escherichia coli (E. coli) established on Mie scattering theory, we can obtain the bacteria size by the normalized spectra interpretation, and calculate a single bacterium’s reference spectra. Based on the relation curve between the measured spectra and a single bacterium’s reference spectra, we can obtain the bacterial concentration and analyze the accuracy of the bacterial concentration by several normalization procedures. Compared with plate counting, the bacterial concentration calculated by the average normalization has the maximum relative error of 0.92%, the average relative error of 0.70%, and the correlation coefficient of 0.9984. The accuracy and stability of the method are the best. The study can provide the basic data for the quantitative detection and early warning of bacteria in water.

We use the new external cavity widely-tuned quantum cascade laser (ECQCL) as the excitation light source and the high frequency quartz resonant tuning fork as the photoelectric detector to study the quantitative analysis and composition identification of volatile organic compounds (VOCs) by mid-infrared laser spectroscopy. The infrared absorption spectra of different types of gasoline samples from different sites are carefully analyzed and compared with the standard spectra taken from the Pacific Northwest National Laboratory (PNNL) database. The results are very consistent. In this experiment, a self-established spectral analysis model integrated with one dimensional cubic spline interpolation algorithm (CSIA) and multiple linear regression algorithm (MLRM) is developed and successfully used for quantitative analysis and component identification of VOCs.

The chemical properties of sodium nitrate are stable, and the Raman characteristic peaks of sodium nitrate and potassium sorbate can be separated completely. The Raman spectrum of potassium sorbate, a preservative commonly used in food, is calibrated with Raman spectrum of sodium nitrate, whose characteristic peak at Raman shift 1053 cm-1 of sodium nitrate with mass fraction of 0.1 is used as internal standard peak. We calculate the relative ratios of the intensity of internal standard speak and characteristic peak intensities of the same concentration sodium nitrate in 49 samples respectively, use the relative ratios to correct characteristic peak intensities of potassium sorbate in 49 samples, and establish the quantitative prediction model of potassium sorbate by linear regression. The results show that the correlation coefficients of calibration set and prediction set significantly improve after correction. The squares of correlation coefficients of potassium sorbate at 1399 cm-1 characteristic peak are 0.9885 and 0.9865, the root mean square errors are 3.0384×10-3 and 3.7643×10-3 for calibration set and prediction set, respectively. Based on the optimal prediction model, we predict 18 new samples. The square of correlation coefficient of the predicted and real values is 0.9799 and root mean square error is 4.8702×10-3, which indicate that the internal standard method of sodium nitrate can effectively reduce the influences of detection instrument, detection environment, and human factors on the Raman peak intensity of potassium sorbate, and can improve the accuracy of the predicted model.

In order to analyze the surface-enhanced Raman scattering (SERS) electromagnetic enhancement properties of Ag nanoparticles (AgNPs)/carbon nanotubes (CNTs) composite structure, we establish the AgNPs/CNTs simulation model by FDTD Solutions software and simulate the electric field distribution of AgNPs/CNTs by changing the size of silver nanoparticles, the gap between two AgNPs, and the excitation wavelength. The simulation results show that there are two kinds of “hot spots” for AgNPs/CNTs composite structure, one existing between CNTs and AgNPs, and the other existing between two AgNPs on CNTs surface. It is found that, with the increase of AgNPs size, the maximum electric field intensity first increases and then decreases; with the increase of the gap between two AgNPs, the intensity of the electric field decreases; when the excitation wavelength is 532 nm, the electric field intensity around AgNPs/CNTs is the strongest. It is concluded that, taking the SiO2 film as the base material, when the size of AgNPs is 60 nm, the gap is 2 nm, and the excitation wavelength is 532 nm, the electric field intensity is the strongest and the calculated enhancement factor is about 10 8. The theory and experiments show that SERS enhancement effect of the Ag film is better than that of the SiO2 film.

In order to solve the problem of the influence of noise on model accuracy and stability in detecting materials content using near infrared spectra, we introduce the generalized S transform and singular value decomposition (SVD). Firstly, we use the generalized S transform to obtain time-frequency spectra of spectral data, and then use the two-dimensional time-frequency coefficient matrix as the Hankel matrix of SVD to solve singular values. Secondly, we use the k-means clustering algorithm to classify the singular value sequence and determine the reconstructed singular values. Finally, the de-noised coefficient matrix is transformed by the generalized S inversion to obtain de-noised spectral data. The basic theory and realization process of the combination method are given, and simulated data and the first derivative spectrum of wheat gluten are de-noised with the combination method. The results are compared with the traditional 9-point smoothing method and wavelet soft thresholding method. It is found that the proposed method overcomes the limitation of single dimension filtering (time domain or frequency domain), and does not need to reference noise data and select the base function. In the de-noising of wheat gluten derivative spectra, only 2 singular values are enough to achieve better de-noising effect, which reduces the complexity of the filtering process. The accuracy of the near infrared spectrum analysis and the robustness of the proposed model are better than those of the traditional 9-point smoothing method and the wavelet soft thresholding method. The predictive coefficient of the prediction set of the proposed method is 0.9985, which is larger than that of the 9-point smoothing method (0.9436). The root mean square error of the proposed method is 0.0406, which is smaller than that of the 9-point smoothing method (0.0843). The accuracy of quantitative detection of moisture content in wheat gluten is improved obviously.

We propose a photonic approach to generate phase-coded signal with tunable frequency multiplication factor based on cascaded Mach-Zehnder modulators (MZMs). The key component in the system is the cascaded MZMs. We can select the ±k-order (k=1,2,…,5) sidebands by controlling the direct current(DC) bias voltage and modulation index of the two MZMs. We use programmable optical filter to filter the ±k-order (k>5) sidebands, and then combined with the phase modulation, can generate the phase-coded signal with frequency multiplication factors of 2, 4, 6, 8, and 10. In the proposed system, we can change the amplitude of the RF-driven signal applied to the cascaded MZMs to adjust the frequency multiplication factor by changing the amplitude of the RF driven signal of the cascaded MZMs. The scheme is more compact and flexible. The feasibility of this approach is demonstrated through a simulation experiment. The simulation results show that we can generate the phase-coded signals with frequencies of 32 GHz and 40 GHz using a 4 GHz microwave signal source. It means that we achieve the frequency multiplication factors of 8 and 10. Meanwhile, the pulse compression capability of the generated phase-coded signal is also demonstrated to be very well.