The direction rule of the laser beam traveling through a deflected polarizing beam splitter (PBS) cube is derived. It reveals that, due to the influence of end-face reflection of the PBS at the detector side, the emergent beam coming from the incident beam parallels the direction of the original case without rotation, with only a very small translation interval between them. The formula of the translation interval is also given. Meanwhile, the emergent beam from the return signal at the detector side deflects at an angle twice that of the PBS rotation angle. The correctness has been verified by an experiment. The intensity transmittance of the emergent beam when propagating in the PBS is changes very little if the rotation angle is less than 35 deg. In a 3D imaging lidar system, by rotating the PBS cube by an angle, the direction of the return signal optical axis is separated from that of the origin, which can decrease or eliminate the influence of direct reflection caused by the prism end face on target return signal detection. This has been checked by experiment.

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