Simultaneous temperature and vibration monitoring using an all-PM fiber loop mirror interferometer

In this work, an all-polarization maintaining fiber loop mirror interferometer is presented and validated as vibration and temperature sensor without crosstalk between measurands. The system is entirely built using polarization-maintaining (PM) fiber and a PM optical coupler. As a consequence, no polarization controllers are needed in the cavity, significantly simplifying the operation of the system and improving the stability and accuracy of the measurements. The loop comprises three PM fiber sections appropriately fused with an angle offset between them. In this manner, the interference is maximized and the sensing contributions of the two PM fibers used as communications channels are suppressed. The third PM fiber is used as the sensor itself, simultaneously monitoring temperature and mechanical vibration up to 1.2 kHz by means of an interrogation technique based on fast Fourier transform.