Mitigating polarization effects in coaxial coherent LiDAR for enhanced signal power

This paper presents a systematic quantitative analysis of polarization effects on the received optical signal power for detection in coaxial coherent LiDAR systems. In a coaxial configuration, an optical circulation function is required to separate the received (Rx) signal from the transmitted (Tx) beam with a linear polarization, enabling coherent detection through mixing with a local oscillator (LO) of matched polarization. This separation is achieved by the function of a polarization beam splitter (PBS) to isolate the Rx signal from the Tx path. For ideal surfaces with 100% depolarization, half of the signal reaching the PBS is collected for mixing with the LO. Target surfaces with different depolarization characteristics are modeled using the Mueller matrix formalism. Analysis shows that polarization effects-arising from both target surface’s depolarization and birefringence in the LiDAR optical path-can significantly degrade the Rx optical power split from the PBS for mixing. With a 90° polarization rotation via double-passing propagation through a polarization component following the PBS in the Tx path, the system is more robust against polarization effects.