mHz~kHz甚低频1/f噪声是限制超长光纤干涉仪测量精度的主要因素,厘清干涉仪1/f噪声的产生来源和分布规律是抑制测量噪声、提升观测精度的重要前提。为此,搭建了超百米臂长、全对称、差分探测的保偏光纤马赫-曾德尔干涉仪,通过开展基于不同类型窄线宽激光器和不同长度敏感光纤的干涉仪噪声测量实验,分别确定了光源频率噪声和光纤热噪声引起的干涉仪甚低频相位噪声谱分布特性;在此基础上,开展了超长光纤干涉仪1/f相位噪声谱分布规律研究。实验结果表明:260 m光纤马赫-曾德尔干涉仪的相位噪声幅值从μrad/Hz ^1/2@1 kHz量级快速上升到10 mrad/Hz ^1/2@1 mHz量级,它由光源频率漂移和光纤热噪声共同决定。从而证实了在mHz~kHz频段内,超长光纤干涉仪相位噪声服从1/f^1+β的谱分布规律。

The measurement accuracy of ultralong fiber interferometers is mainly limited by the 1/f noise in the ultralow frequency band from mHz to kHz. The sources and distribution principle of 1/f noise need to be thoroughly studied to suppress measurement noise and improve measurement resolution. For this reason, a balanced polarization-maintaining fiber Mach-Zehnder (M-Z) interferometer was built for differential detection, in which the arm length is over 100 m. By testing optical fibers with different lengths as well as different types of narrow line-width laser utilizing this interferometer, we obtained the distribution characteristics of ultralow-frequency phase noises respectively induced by laser frequency drift and fiber thermal noise on the spectra. According to the experimental results above, the distribution principle of 1/f noise in the ultralong fiber interferometer was also explained. The results show that the amplitude of phase noise increases rapidly from the order of 1 μrad/Hz ^1/2 @1 kHz to the order of 10 mrad/Hz ^1/2 @1 mHz within a 260 m arm-length M-Z interferometer, which is due to the laser frequency drift and fiber thermal noise. It can be concluded that for the frequency band from mHz to kHz, the phase noise of the ultralong fiber interferometer satisfies 1/f^1+β spectral distribution.