Modified orthogonal polarization switching method for broadband response and polarization fading suppression of an interferometric FBG array.

Polarization fading is a key factor limiting the performance of interferometric fiber Bragg grating (FBG) arrays. The orthogonal polarization switching (OPS) method is one of the effective solutions to this problem. However, the conventional OPS method has a critical issue of limited frequency response, which restricts the system's application in broadband scenarios. This paper proposes a modified OPS method. By designing four new construction matrices, this method realizes cross-splicing of four polarization signals, simultaneously achieving a 4-fold improvement in signal sampling rate and polarization fading suppression. A 7-element interferometric FBG array sensing system based on the modified orthogonal polarization switching method is established. In the experiment, the visibility of the interference signal is maintained above 0.9 under polarization disturbance. Under the condition of a 100 kHz pulse repetition frequency, successful reconstruction of an 18 kHz vibration signal is achieved, breaking the 12.5 kHz frequency response upper limit of the conventional OPS method, which confirms the effectiveness of the modified method. This method provides technical support for the application of interferometric FBG time-division multiplexing arrays (especially quasidistributed and distributed fiber sensors) in low-noise and broadband scenarios.