Large Range Dynamic Phase Extraction of Extrinsic Fabry-Perot Interferometric Sensors Using Phase-Step Insensitive FM-PSI

In this article, we propose a phase-step insensitive frequency modulated phase shifting interferometry (FM-PSI) for large range dynamic phase extraction of extrinsic Fabry-Perot (F-P) interferometric sensors. A modulated grating Y-branch (MG-Y) laser is employed to achieve fast and programmable phase shifting. In order to extend the dynamic range of the conventional quadrature phase demodulation scheme, it is necessary to consider the real-time dynamic changes of the phase shift step, reflected light intensity, and interference contrast when the cavity length changes over a wide range. Herein, we introduce equal phase difference by fast switching of four optical frequencies with fixed frequency intervals, and calibrate the laser injection current to keep the output power at different optical frequencies consistent, thereby mitigating the influence of light intensity modulation effect. Combined with the 4-step Carre algorithm, fast and large dynamic range phase demodulation is realized while the initial cavity length and phase shift step are unknown. Furthermore, the proposed FM-PSI serves as an ideal choice for the simultaneous measurement of multi-channel dynamic interferometric sensors. Simulation and experimental results show that the technique can detect large-amplitude vibrations and monitor multi-dimensional dynamic displacements.