Polarization-Maintaining Photonic Crystal Fiber Vibration Sensor Based on Polarization-Diversified Loop Structure with Improved Frequency Response

We investigated the frequency response of a polarimetric fiber vibration sensor based on a polarization diversified loop structure according to the length of polarization-maintaining photonic crystal fiber (PM-PCF) used as a sensor head. The fiber vibration sensor was fabricated using a polarization beam splitter, PM-PCF, and two waveplates, that is, a quarter-wave plate and a half-wave plate. For intensity-based vibration measurement, a laser diode and a photodetector were utilized for the realization of the sensor system. The single-frequency vibration was applied to the sensor head by using a piezoelectric transducer. Over a frequency range of 1-3000 Hz, the frequency response of the fabricated sensor was observed for three kinds of sensor head lengths of 6.2, 8.4, and 12.2 cm. In measured frequency responses, a resonance peak appeared at 140 Hz irrespective of the PM-PCF length, but cut-off frequencies were measured as similar to 538, similar to 386, and similar to 228 Hz for PM-PCF lengths of 6.2, 8.4, and 12.2 cm, respectively. The phase shift per unit strain and the minimum detectable strain perturbation were measured as similar to 0.291 mrad/mu epsilon and similar to 0.392 n epsilon/Hz(1/2) at 2000 Hz for 6.2-cm-long PM-PCF, respectively.