Suppressing the influence of GM-APD coherent lidar saturation by signal modulation

Geiger-mode Avalanche Photo Diode (GM-APD) coherent lidar improves coherent detection sensitivity to single photon level, which is more suitable for remote target detection. However, due to the limited pixels, the photon count will be affected by the system saturation, resulting in low utilization of local oscillator (LO), reducing the system's signal-to-noise ratio (SNR). A GM-APD coherent lidar system based on signal modulation is proposed, the method uses an electro-optic modulator to modulate the slope of signal light, then GM-APD coherent detection. Firstly, the detection and optimal parameter model based on signal modulation are derived. Secondly, the effectiveness of this system is analyzed through simulation. Finally, GM-APD coherent detection experiment based on signal modulation is carried out to verify the effectiveness of the system. When the echo position is 2 μs, the pulse width is 200 ns, the number of signal photons is about 8000, LO photons is about 820, signal modulation improves the system SNR by more than two times. It is concluded that the greater influence of saturation on GM-APD coherent lidar, the better signal modulation effect. The proposed scheme improves the utilization rate of LO and SNR from equipment level, to further enhance system detection ability.