Research On Non-line-of-sight Imaging Technology Based On Single Photon

Compared with the traditional imaging technology,non-line-of-sight imaging is mainly aimed at detecting hidden targets.Due to its ability to bypass or pass through occluding objects to image targets outside the field of view,it has huge advantages in some occasions with special needs.Value.Since the laser undergoes at least three reflections in the entire non-line-of-sight imaging process,its amplitude and phase information cannot be fully preserved.It is necessary to accurately distinguish the background noise,the intermediate reflection surface signal and the useful scattering signal of the hidden object.Resolution detectors,lasers,etc.all have high requirements.Time-Correlated Single-Photon Counting(TCSPC)is a very weak optical signal detection technology,which uses time-amplitude converter and analog-to-digital converter or time-to-digital converter to detect the flight of photons Time to achieve high-precision measurement of time intervals.Combining non-line-of-sight imaging and single-photon detection techniques can greatly improve detection sensitivity,allowing the use of lower-power semiconductor lasers for long-range detection.In this paper,non-line-of-sight imaging and single-photon detection technology are combined,and an Field Programmable Gate Array(FPGA)based precise synchronization control module is designed,and a non-horizontal single-photon imaging system is built.The main research contents and results of this paper are as follows:(1)A set of non-line-of-sight imaging single-photon imaging system is built.The system is mainly composed of picosecond pulse laser,single photon detector,beam splitter cube,two-dimensional galvanometer,quarter wave plate,TCSPC module,and FPGA.A precise synchronization control module based on FPGA is developed.The arrival time of the photon pulse can be divided into coarse time and fine time,where the coarse time is obtained by the self-designed FPGA module,and the fine time is the time when the photon pulse reaches the nearest laser pulse,which is obtained by TCSPC measurement.(2)For non-line-of-sight imaging,the simulation technology combining Monte Carlo simulation and geometric ray tracing method is studied.From the perspective of photon counting,the trajectory of photons is tracked through the bidirectional scattering distribution function and the scattering image function.The simulation data is reconstructed by the light cone transformation reconstruction algorithm,and a good denoising effect is obtained.The influence of the number of photons,the photon flight distance,and the characteristics of the intermediate surface on the imaging accuracy is further compared to solve the high-precision and accurate imaging system.Modeling technical difficulties.(3)Carry out experimental research on reflectivity and depth imaging performance calibration,and conduct reflectivity and depth imaging experiments on intermediate surfaces with different reflectivity,different scanning times and laser intensities.For image reconstruction,time-gating and light cone transformation algorithms are used for joint optimization,which realizes high-sensitivity non-line-of-sight single-photon imaging,and realizes the reconstruction of reflectance maps and depth maps with a resolution of up to 128×128 pixels.Finally,we have built a non-line-of-sight imaging based on compression sampling where the mechanical scanning is replaced by a Digital Micro-mirror Device(DMD).In this way,non-line-of-sight imaging can be used to analyze the photon transmission processes and experimental results,in turn,provide more possibilities to achieve non-line-of-sight imaging.