Rapid identification and detection of gases is a major problem that needs to be solved urgently by researches from worldwide. With the development of optical technology, optical gas detection technology has attracted great attention due to its remarkable advantages of high efficiency, multi-component detection ability and high sensitivity. In this paper, the theoretical foundation of optical gas detection technology is first introduced. Then the working principles and applications of various optical detection technologies for typical gases according to active and passive detection are reviewed. Using these gas detection technologies, dozens of gases have been continuously monitored at long distance with high sensitivity. The measurements of gas composition, concentration, temperature and other parameters in a variety of scenarios are realized, which effectively reduces the occurrence of dangerous accidents. By summarizing and analyzing the technical problems that still exist in the current optical gas detection technology, the future development trend is prospected.

In the adaptive optics system, the piezoelectric steering mirror(tip/tilt mirror, TTM) is usually used to correct the wavefront aberration caused by atmospheric turbulence in real time. However, the response of the piezoelectric tilting mirror has large nonlinear hysteresis effect, which greatly reduces the precision of the tilting mirror in place, affects the stability of the system, and restricts the bandwidth of the skew correction system. Therefore, the hysteresis phenomenon needs to be modeled and compensated by the established model. In this paper, hysteresis operator is introduced and using Bayesian regularization training algorithm to train BP (back propagation) neural network to construct hysteresis model of piezoelectric steering mirror. Then experimental study was conducted on a piezoelectric steering mirror developed by Institute of Optics and Electronics, Chinese Academy of Sciences. The final experimental results show that the hysteresis model of piezoelectric steering mirror constructed by BP neural network has more accurate identification capability, the hysteresis size in the X direction decreased from 6.5% to 1.3% and that in the Y direction decreased from 7.1% to 1.6%.

Aiming to the problems of traditional active electromagnetic transformer such as easy magnetic saturation, poor stability and anti-interference ability, and limited installation, etc., this paper designs the optical fiber current transformer to measure current by rotation angle based on Faraday magneto-optic effect; HB Spun optical fiber is used as sensing element without saturation and can be used for high current measurement. The designed transformer uses the optical reciprocity loop to eliminate the interference of temperature and optical fiber defect on the measurement of optical rotation angle, and uses reflector to enlarge the optical rotation angle to four times, which can realize accurate measurement of small current; Sensing element uses flexible fiber ring with shape variability characteristic, which helps for measurement of current in complex space. The paper compares flexible fiber ring with different loops to standard current transformer, the results show that optical reciprocity loop can eliminate the interference of temperature on the current measurement and the accuracy of all-fiber current transformer is 0.5 in the range of -5 ℃～70 ℃, which can realize the accurate measurement of small current.

The geometry parameters of optical fiber affect the optical transmission and mechanical properties, which are the important indexes to measure the quality of fiber. Near-field light distribution method is recommended in GB15972.20-2008 for the measurement of geometry parameters. In order to distinguish the boundary between fiber core and cladding, the method needs to illuminate the fiber. The end face of the fiber core is a bright spot with unclear edge, so the true edge of the core and cladding cannot be accurately judged. In this paper, the distribution of mode field in optical fiber is analyzed. Theoretically, the solution of electromagnetic vector of mode field satisfies Bessel function, but Gaussian function can also be used under approximate conditions. Therefore, Gaussian function is used to fit the distribution of the fiber core in this paper, and the real edge of the fiber core and cladding can be obtained from the Gaussian function after fitting. This method is a further improvement on the measurement method of GB15972.20-2008. The experimental results show that when the cutting effect of the fiber is not good or the imaging quality is poor, the Gaussian function method fitting with mode distribution can still ensure the repeatability of the measurement and the stability of the measured data.

In order to obtain better super-resolution reconstruction results of depth images, this paper constructs a multi-scale color image guidance depth image super-resolution reconstruction convolutional neural network. In this paper, the multi-scale fusion method is used to realize the guidance of high resolution (HR) color image features to low resolution (LR) depth image features, which is beneficial to the restoration of image details. In the process of extracting features from LR depth images, a multiple receptive field residual block (MRFRB) is constructed to extract and fuse the features of different receptive fields, and then connect and fuse the features of each MRFRB output to obtain global fusion features. Finally, the HR depth image is obtained through sub-pixel convolution layer and global fusion features. The experimental results show that the super-resolution image obtained by this method alleviates the edge distortion and artifact problems, and has better visual effects.

Starting from the expression of Laguerre-Gaussian vortex beam and based on Rayleigh diffraction theory, the variation of rotating coherence function of vortex beam propagating in atmospheric turbulence is studied. The crosstalk between the angular momentum of each orbital angular momentum when the vortex beam propagates in atmospheric turbulence is summarized. The topological charge detection probability is used to describe the crosstalk law, and the analytical expression of the topological charge detection probability is derived. The distribution of topological charge number of vortex beam passing through turbulence is studied, and the results are compared with the numerical simulation results of vortex beam passing through atmospheric random phase screen. The relationship between the detection probability of the theoretical and simulated topological charge numbers with the turbulence intensity and the topological charge number of the initial vortex beam is compared, and the correctness of the analytical expression of the topological charge number detection probability is verified. Through this expression, the interaction between atmospheric turbulence and vortex beam can be further studied, which can affect the essence of angular momentum scattering of vortex beam, and the suitable topological charge number interval can be selected for the space optical communication of vortex beam. It also provides a theoretical basis for selecting the appropriate beam waist size under different turbulence intensities to reduce the bit error rate (BER) caused by crosstalk.

Transient measurements of high-speed airflow field are needed in the measurement of boundary layer. Digital interferometry can measure flow field quantitatively to obtain density information, which is very necessary in flow field measurement. In this paper, a common-path shearing interferometry method is introduced. It is insensitive to vibration and does not need a reference plane. It is suitable for flow field measurement. A fast algorithm based on spatial phase modulation, coupled with a pulse laser and a synchronous control system, is used to measure the disturbance density field quantitatively in real time. The acquisition resolution of the system is 200 pixels × 200 pixels, and the acquisition frequency can reach more than 1000 frames per second. The wavefront reconstruction method of the system has been simulated by computer, and the detection result is better than 1/20λ. The experimental results in a 0.6 m wind tunnel show that the system can restrain the vibration interference and distinguish the disturbance signal and the vibration noise remarkably. It has good application prospects.

A cylindrical image mosaic method based on fast camera calibration in multi-scene is proposed to solve the problems of scene limitation and complex calibration process in image mosaic using camera calibration parameter. Firstly, the accurate corner feature of checkerboard calibration board is used to make it in the overlapping field of view of two adjacent images. Then, the image sequence is pre-processed by corner extraction, precision and matching, so that the registration parameters between the images to be stitched can be solved accurately and quickly. After that, the cylindrical projection is used to maintain the visual consistency of the images, and the multi-band fusion is used to retain the details of the images. Subsequently, the images are stitched using registration parameters obtained by calibration. Finally, the whole system is built on a low-power embedded platform to accomplish fast calibration and mosaic process based on calibration parameters in multi-scene. The experiment results show that the proposed method can accomplish camera calibration quickly and accurately in indoor and tunnel scenarios, and the image mosaic process is time-consuming. Meanwhile, it can ensure better stitching accuracy and imaging effect, and has strong robustness.

In order to analyze the performance of vehicle positioning using LED traffic lights in foggy environment, the influences of receiving angle, road width, and signal-to-noise ratio (SNR) at the receiver in foggy environment on vehicle positioning range are discussed. The simulation results show that the optimal signal reception angle is 25°; when the vehicle is within 20 m of the LED traffic light, the road width has a greater impact on the received power of the signal; near the traffic light, the positioning distance of the vehicle on the second lane is 2.2 m shorter than that of the vehicle in the first lane; the SNR of the receiver at night is better than during the day, and the positioning range at night is greater than during the day; compared with sunny weather, the SNR in the fog days decrease significantly, which will greatly affect the positioning range of the vehicle, so to ensure safe driving, vehicles need more braking time when driving in foggy days.