Improving the signal-to-noise ratio of GM-APD coherent lidar system based on phase synchronization method

Abstract

Geiger mode avalanche photodiode (GM-APD) coherent lidar is a new coherent detection system for obtaining multidimensional information. The system can increase the detection sensitivity to the level of a single photon, which is the main technical direction of long-distance laser detection. The system noise of GM-APD follows a Gaussian distribution. Hence, the time-domain cumulative signal-to-noise ratio is much higher than that of the spectrum cumulative, but the jitter of the multipulse echo phase limits the system’s ability to accumulate time-domain signals. This paper proposes a phase synchronization method to solve the abovementioned problem. First, the system achieves multipulse phase consistency by introducing a clock stable and synchronized radio frequency source as well as a pulse signal externally triggered by an acousto-optic modulator. A theoretical model of the method is established. Second, the phase distribution of the system is monitored using a double-balanced detector, and the period of the system’s phase distribution is obtained, thereby verifying the abovementioned theoretical analysis. To verify the feasibility of the method, the GM-APD coherent lidar experimental system is used to detect the all-fiber system and targets. This work addresses the problem of the system being unable to perform time-domain accumulation because of the randomness of the system’s multipulse phase. This framework reduces the required time for the subsequent algorithm, yielding improved real-time performance.