편광 상이 고리 구조를 기반으로 하는 광섬유 진동 센서의 주파수 응답 특성에 관한 연구

Abstract

Here we demonstrated a polarimetric fiber vibration sensor (FVS) based on a polarization-diversified loop, which had an enhanced frequency response, using short polarization-maintaining photonic crystal fiber (PM-PCF) employed as a sensor head. The fabricated FVS is composed of a polarization beam splitter for forming a polarization-diversified loop, PM-PCF, and two polarization modulators, that is, a quarter-wave plate and a half-wave plate. For high-speed vibration sensing, intensity-based vibration measurement was performed using a laser diode and a photodetector. Three PM-PCF segments with longitudinal fiber lengths of 3.0, 6.5, and 11.6 cm, one of which was employed as a sensor head, were utilized to investigate the effect of the PM-PCF length on the frequency response of the fabricated sensor. In this investigation, single-frequency vibration ranging from 1 to 3000 Hz was applied to the sensor head using a piezoelectric transducer. For three measured frequency responses, the same resonance frequency was observed at 400 Hz, and the dependence of the frequency response on the sensor head length was evident in a frequency range of 700 to 2500 Hz. In particular, cut-off frequencies were measured to be ~1670, ~1182, and ~780 Hz in the three frequency responses for 3.0-, 6.5-, and 11.6-cm-long PM-PCF segments, respectively. That is, it was found that the cut-off frequency increased with the decrease of the sensor head length, allowing the frequency response to be broadened. Consequently, we conclude that a short sensor head in the fabricated FVS can provide an improved frequency response, which offers a better signal to noise ratio over the resonance frequency, in addition to the convenience of installation and the reduced sensitivity to external perturbations.