Research On Key Technique Of The Single Photon Imaging And Detection

In recent years, the three-dimensional imaging laser radar with the advantages of fast imaging speed, fine angular resolution, high range resolution, and small divergence angle is rapidly developing in the field of military and civilian. The laser radar using the scannerless active laser three dimensional (3D) imaging technology with detector array, which can meet the system requirements of the rapid and stable imaging, low system power consumption, low system weight, and small volume, has been become the main developed direction of current3D imaging laser radar. For scannerless3D imging laser radar, the echo intensity of the remote non-cooperative target is very weak, therefore, the echo photons impinging into each pixel of the detector array is very few, even single photon. The avalanche photodiode operating in the Geiger-mode (GM-APD) with the advantages of single photon sensitivity, all solid state structure, high gain, fast response speed, small volume, low weight, low power consumption, and good working stability is suitable for detecting this weak echo. At the same time, due to extremely high avalanche gain, the output of the GM-APD can directly drive the subsequent digital signal processing circuits, and the benefits of the GM-APD are its ability to minimize the integrated circuit size and enable a growth path to large-format arrays that is the key device for scannerless3D imaging laser radar. However,3D imaging laser radar based on GM-APD array is still in the developing stage, the system detection theory is still not perfect; to meet the strict requirements of application, new methods and technologies are constantly being proposed. So, in this thesis, we have done some depth research and analysis on the basic theory and detection performance of the direct detection photon pulsed laser radar and photon pulsed heterodyne detection system based on GM-APD, some original results have been demonstrated, and the main researched contents and their achievement are as follows:On basis of the optical properties of target and relationship of beam, the laser radar equation is used, and the relationship between the echo photons and detection distance is investigated. Based on the semiclassical theory of the photoelectric detection, the statistical law of echo photons is studied, the rule of the negative-binomial distribution (NBD) and Poisson distribution and their trnsformation conditions is anlyzed, and these studies provide a basis for investigating the system detection performance.Based on the designed structure of the direct detection pulsed laser radar using GM-APD as detector, according to the system working principle, detection time sequence, and the relation between the echo pulse width and resolving time of the time-to-digital converter (TDC), the target detection probability and false alarm probability are investigated. Results show that stronger echo intensity, narrower echo pulse width, lower noise, and more front echo position result in better detection performance with higher target detection probability and lower false alarm probability.To mostly eliminate the influence of various interferences, the system minimum acceptable detection probability is set. Based on this minimum acceptable detection probability and Poisson statistical model of the echo primary electrons, and the theoretical model of the system maximum detection range is established. By using the system design parameters, the influence of five main factors on the maximum detection range is investigated. The results show that the stronger emitted pulse energy, lower noise level, front echo position in the range gate, large atmospheric transmission, and high target reflectivity can result in larger maximum detection range, and it is important to select the minimum acceptable detection probability for producing a larger maximum detection range and a lower false-alarm probability.Range accuracy is one of the important parameters for evaluating the performance of the pulsed laser ranging system, According to the statistical theory and centroid method, the theoretical model of range accuracy is established. Using the system design parameters, the influence of the echo intensity, pulse width, noise, and echo position on the range accuracy is discussed. The results shows that echo intensity and pulse width are the main influence factors, stronger echo intensity and narrower pulse width can bring higher range accuracy.The false alarm is lower, the system detection performance is better. The multi pulse accumulation algorithm which can be used to improve the system detection performance and reject the false alarm is presented. Based on the probability model of AND logic, OR logic, and mixed AND and OR logic, the role of the dual detector structure for improving system detection performance is investigated. The results show that stronger echo intensity, narrower echo pulse width, lower noise, and more front echo position result in better detection performance. Using dual detector structure, the false alarm can be well suppressed with AND gate, the target detection probability can be improved with OR gate, and higher target detection probability and lower false alarm can be achieved with AND gate and OR gate.To obtain more target information, a combined system of heterodyne detection with laser pulse and photon counting based on Geiger-mode avalanche photodiode (GM-APD) is proposed. Based on the heterodyne principle and statistical detection theory of photon counting, the range accuracy model is established. The factors that influence the range accuracy, namely pulse width, echo intensity, local oscillator (LO) intensity, noise, echo position, and beat frequency, are discussed. Finally, based on the random phasor and amplitude vector theory, the photon counting is transformed into the frequency domain, the SNR of the photon pulsed heterodyne detection system is investigated. The results show that these six factors have significant influence on the range accuracy when the echo intensity is extremely weak. In case that the primary electrons of the echo signal are beyond4, the pulse width and echo intensity are the main influence factors. It is also shown that the stronger echo intensity, narrower pulse width, low noise, large echo position, and small beat frequency produce higher range accuracy in a pulsed photon heterodyne detection system based on GM-APD.