Dual-Polarization Fiber Optic Differential Interferometer for High-Sensitivity Sensing Applications

The fiber optic differential interferometer (FODI) is a sensor capable of direct detection of temporal derivatives of measured physical quantities. However, its phase sensitivity is currently constrained by the presence of relative intensity noise (RIN). In this study, the disruptive effects of RIN are evaluated through theoretical analysis. Based on this analysis, a novel dual-polarization fiber optic differential interferometer (DP-FODI), in which a dual-polarization front-end is integrated with a new differential fiber sensing probe, is proposed. The mechanism for RIN suppression is comprehensively elucidated through theoretical analysis and numerical simulations. In the static self-noise tests of DP-FODI employing a delay fiber length of 2 km, successful RIN suppression is achieved, leading to a 10-fold enhancement of phase sensitivity from 1.6\times 10^{-6} \mathrm{rad/\sqrt{Hz}} to 1.5\times 10^{-7} \mathrm{rad/\sqrt{Hz}}. Furthermore, dynamic experiments were conducted to validate the differential characteristics of DP-FODI, realizing a dynamic range exceeding 106 dB. DP-FODI exhibits significant potential for application in various domains, including strain monitoring and underwater acoustic measurement.