Abstract
We report on phase interrogation of extrinsic Fabry-Perot interferometric (EFPI) sensors through a wavelength-switched unit with a polarization-maintaining fiber Bragg grating (PMFBG). The measurements at two wavelengths are first achieved in one total-optical path. The reflected peaks of the PMFBG with two natural wavelengths are in mutually perpendicular polarization detection, and they are switched through an electro-optic modulator at a high switching speed of 10kHz. An ellipse fitting differential cross multiplication (EF-DCM) algorithm is proposed for interrogating the variation of the gap length of the EFPI sensors. The phase demodulation system has been demonstrated to recover a minimum phase of 0.42 μrad/Hz at the test frequency of 100Hz with a stable intensity fluctuation level of ±0.8 dB. Three EFPI sensors with different cavity lengths are tested at the test frequency of 200Hz, and the results indicate that the system can achieve the demodulation of EFPI sensors with different cavity lengths stably.
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