Voltage demodulation and vibration monitoring based on a polarization maintaining fiber loop mirror

Wavelength demodulation for a polarization maintaining fiber loop mirror sensor using an optical spectrum analyzer is not only expensive but also not suitable for vibration monitoring. In this work, we demonstrate a voltage-based polarization maintaining fiber loop mirror sensor demodulation principle. In our experiments, we observed that the light intensity from the output interference spectrum at a certain wavelength increased with increasing strain. To remove the expensive optical spectrum analyzer, we converted the light intensity signals into voltage signals using a photo-detector. The obtained demodulation linear sensitivity was 1.19 mV/µε. Compared with fiber Bragg grating sensors, the sensitivity in our system was improved greatly. Furthermore, the polarization maintaining fiber loop mirror was applied to vibration monitoring. A vibration exciter was attached underneath the specimen for use as a vibration source. A laser displacement sensor was used for comparison. The experimental results show that the polarization maintaining fiber loop mirror performs better at high frequencies than the laser displacement sensor, and that signals below 20 Hz measured by the polarization maintaining fiber loop mirror were distorted as a result of exceeding the measurement range. In addition, we have proposed further decreasing the distortion by reducing the polarization maintaining fiber length and fabricating a polarization maintaining fiber loop mirror sensor with a different dynamic measurement range by adjusting the polarization maintaining fiber length.