An ERPNS Technology Based on OFDR for Accurate Arm-Length Difference Measurement of Optical Fiber Interferometer Under Dynamic Environment

Accurate measurement of interferometer arm-length difference is very important in the application fields such as fiber optic hydrophones. However, the interferometer is very sensitive to the environmental vibration and noise, which affects the accuracy of the interferometer measurement. A novel environmental random phase noise separation (ERPNS) technology is proposed to effectively reduce optical frequency domain reflectometer (OFDR)’s sensitivity to environmental vibration for the measurement of the fiber interferometer. A set of optical paths based on dual-laser coherent detection technology and the related ERPNS algorithm was developed to extract the environmental phase noise from the measurement data. The OFDR's sensitivity to vibration is decreased by ∼60 dB in theory and a measurement accuracy better than 0.05 mm for the static arm length difference of 74.51902 m in different dynamic environment is achieved experimentally, with 56 μm of spatial resolution in the maximum detectable distance of about 75 m.