Simultaneous Interrogation of Multiple Mach-Zehnder Interferometers Without Crosstalk Based on the Reconstructed Microwave Photonics Filters

This paper proposes and experimentally demonstrates a crosstalk-free sensing system for multiple fiber-optic interferometers (FOIs), leveraging frequency-time mapping and the reconstructed microwave photonics filters (MPFs). Three Mach-Zehnder interferometers (MZIs) with delay lines are cascaded in series to generate three single-passband MPFs. Owing to the similarity in their free spectral ranges (FSRs), the S21curves exhibit overlap, resulting in crosstalk in demodulation. To resolve this overlap and distinguish the individual MZIs, the superimposed S21curve is first processed using inverse fast Fourier transform (iFFT), yielding the time domain curve, in which these MZIs become distinguishable via their unique delay times. Subsequently, rectangular windowing is applied to isolate the time domain signal components corresponding to each MZI, and a follow-up FFT is performed to reconstruct the individual MPFs of the three MZIs, enabling simultaneous crosstalk-free interrogation. To validate the system's performance, experimental verification under transverse load, axial strain, and temperature are performed. Results show that the sensing sensitivities are -3.94×10-2dB/g, -0.360 MHz/μϵ, and -3.1349 MHz/°C when the heating fiber length is 0.3 m, respectively, which are relatively close to the sensitivities reported in previous studies.