Research On Programmable Chirped Amplitude Single Photon Laser Radar System

Laser radar has wide applications in many fields such as astronomical observation, weather forecasting, communications, target tracking, precision guidance, precise distance measurement,3D imaging, etc. chirp modulation single photon laser radar, with its high precision, high sensitivity, low peak power, and many other advantages attracted many scholars all around the world, but the research of chirp laser radar based on the Gm-APD acting as the detector was done late and in the nascent state. carrying out the theoretical study and system construction on the Gm-APD chirp modulation photon laser radar system is necessary.Firstly, considering the inherent dead time of the single photon detector Gm-APD, which limits the system sample frequency and chirp signal bandwidth, thus leading to the limited improvement in distance precision of the chirp AM single photon laser radar system, this paper puts forward an algorithm of adaptive multiple cycles accumulation(AMCA) to improve the SNR of echo signal, then, the algorithms of the least squares fitting method on the basis of AMCA in time domain and frequency domain are proposed to improve the ranging accuracy of the system. This paper proves in theory that the accumulation of multiple cycles of Gm-APD output signal can improves the SNR of the echo signal. In the frequency domain, combined with AMCA algorithm, this paper also derives a sinc function on the FFT spectrum of the intermediate frequency signal and using the least square fitting to estimate more accurate values of the intermediate frequency. In time domain, combined with AMCA algorithm, a least squares fitting method with intermadiate frequency signal in time domain and frequency domain. In the time domain, the echo signal is reduced as a sinc function after matching filter from the perspective of pulse domain, and so we can estimate the more accurate echo peak position according to fitting the comprssed data in the half peak width with this sinc function. the experiment shows that both two kinds of methods can make the ranging precision of the system getting very big enhancement.Secondly, For the situation where Electro-optic modulator will drift its working point after working a period of time, this paper puts forward a "test-iterative compensation" automatic feedback control algorithm, this algorithm can make the M-Z electro-optic modulator working near the orthogonal for a long time.Thirdly, with the idea of modularization, this paper builds a programmable chirped AM single photon laser radar system based on a set of software and programmable hardware. The system not only allows flexible modification of various system parameters, but also provides safeguard on the rapid development of other laser radar system because of the reusability of each module.At the end of the paper, we study the signal to noise ratio of the system under the condition of different system parameters and analyzes the influence of various system parameters on the system signal-to-noise ratio, what we do above can provides theory and facts for the construction of chirp AM single photon laser radar system.