Sensitivity-Enhanced Optical Fiber Interferometric Phase Demodulation Based on Multipassband Microwave Photonic Filter With Frequency Down-Conversion

A phase sensitivity-enhanced demodulation system for optical fiber interferometers based on a multi passband microwave photonic (MWP) filter is proposed and experimentally demonstrated, which effectively breaks the trade-off between detection frequency and phase sensitivity, enabling the simultaneous realization of high sensitivity and low-frequency detection. In the experimental setup, an optical fiber Fabry–Pérot interferometer (FPI) served as the sensing head, and an additional optical fiber FPI was introduced as a reference. The interference between the two FPIs generated both independent passbands and cross-interference passbands of the MPF, the latter enabling frequency down-conversion. The passband associated with the sensing FPI, initially centered at 1.752 GHz, was translated to 0.537 GHz via the interference between the sensing and reference FPIs, effectively mapping the phase modulation to a lower frequency. Consequently, a 3.26-fold enhancement in the detected phase shift was achieved at 0.537 GHz. Moreover, simultaneous phase demodulation from multiple passbands (e.g., 1.752 and 2.202GHz), down-converted to 1.032 and 0.545GHz, respectively, was successfully realized without spectral interference, demonstrating the scalability of the scheme. This system significantly enhances the detection performance of optical fiber interferometers simply and cost-effectively, offering a novel and scalable strategy for the design of high-resolution fiber interferometric sensing systems.