Phase Demodulation by Frequency Chirping in Coherence Microwave Photonic Interferometry

This article presents a signal processing method to demodulate the optical interference phase of cascaded individual optical fiber intrinsic Fabry-Perot interferometric (IFPI) sensors in a coherent microwave-photonic interferometry (CMPI) distributed sensing system. The new method utilizes the chirp effect of electro-optic modulator (EOM) to create a quasi-quadrature optical interference phase shift between two adjacent pulses which correspond to two adjacent reflection points in the time domain. The phase shift can be controlled by adjusting the bias voltage that is applied to the EOM. The interference phase is calculated by elliptically fitting the phase shift. The interference phase change is proportional to the optical path difference (OPD) change of the interferometer, and the sign can be used to differentiate the increase or decrease of the OPD. The method is demonstrated for distributed strain sensing, showing good linearity, high resolution and large dynamic range.

Automated summary

This article introduces a signal processing method using the chirp effect of EOM to demodulate optical interference phase in a CMPI distributed sensing system. By controlling the phase shift between adjacent pulses, accurate calculation of interference phase and OPD can be achieved. The method demonstrates good linearity, high resolution, and large dynamic range for distributed strain sensing.