Improvement of range accuracy of photon counting chirped AM ladar using phase postprocessing

The photon counting detection of Geiger mode avalanche photodiode is discrete due to its dead time, therefore the intermediate frequency (IF) spectrum is also discrete after the mixing and fast Fourier transform processing. When the peak of the IF spectrum is in the interval of the discrete IF spectrum, it limits the range accuracy without obtaining the exact position of the desired target in the interval. In this paper, the phase postprocessing method is proposed, which extracts not only the frequency of the IF signal, but also the phase of the IF signal that was not exploited before. The theoretical analysis demonstrates significant improvements in the range accuracy of the ladar and the simulation verifies the validity of the method.