Abstract:The fiber of absolute gravimeter laser is easily deflected around the optical axis, due to stress, shape change, vibration or coupler maintenance, etc. The polarization state of the output laser is destroyed, making its transmission in the optical fiber very unstable, resulting in an optical fiber output laser extinction ratio of less than 100, which cannot meet the absolute gravimeter observation conditions. This paper introduces a method of adjusting the optical fiber alignment, and the extinction ratio detection device is designed to check whether the extinction ratio is greater than 100. Alignment adjustment experiments are carried out on the optical fibers of the two WEO100 He-Ne lasers #181 and #250, and we meet the absolute gravimeter measurement conditions by measuring the beam extinction ratio of the output of the two lasers by the extinction ratio detection device. The research shows that the alignment adjustment method is scientific and effective.