Interrogation of Extrinsic Fabry–Perot Sensors Using Path-Matched Differential Interferometry and Phase Generated Carrier Technique

Fiber optic extrinsic Fabry-Perot interferometer (EFPI) sensors utilizing the state-of-the-art MEMS technology have been intensively studied on sensor fabrication for various applications, whereas the signal interrogation technique is still inadequate for some particular applications especially those involving dynamic sensing with high frequency. In this paper, we proposed a white light path-matched differential interferometer system utilizing phase generated carrier (PGC) demodulation method for dynamic EFPI sensors interrogation. A fiber Michelson interferometer (MI) is cascaded with the EFPI sensor as a readout interferometer. One arm of the MI contains a step-motor-assisted movable mirror-collimator pair to realize exactly path matching, and another arm is wound on a piezoelectric transducer ring to introduce the carrier signal for PGC demodulation. The general design principles of the system are presented in detail. Experimental results shown that the sensing signal can be correctly recovered with low distortion. The spectrum level of the phase noise is as low as -103 dB re. rad/√Hz at 1 kHz. The presented interrogation scheme may find promising applications in lots of dynamic EFPI sensing fields, such as acoustic and vibration sensing etc.