Here we experimentally demonstrate a polarimetric polarization-maintaining photonic crystal fiber (PM-PCF) vibration sensor with the shortest sensor head, which shows an enhanced frequency response. The fabricated vibration sensor consists of a polarization beam splitter for forming a polarization-diversified loop (i.e., a kind of Sagnac loop), PM-PCF, and two polarization controllers. For high-speed vibration sensing, intensity-based measurement was carried out using a laser diode and a photodetector. Three PM-PCF segments with lengths of 3.0, 6.5, and 11.6 cm were utilized to investigate the effect of the PM-PCF length on the frequency response of the sensor. In this investigation, single-frequency vibration from 1 – 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 cut-off frequencies were measured as ~2750, ~2100, and ~1630 Hz for 3.0-, 6.5-, and 11.6-cm-long PM-PCF, respectively. That is, the cut-off frequency increases with decreasing sensor head length, allowing the frequency response to be broadened. It is concluded that a short sensor head can provide an improved frequency response and offer a smaller variation of the frequency-dependent amplitude in the sensor output signal within a 3-dB bandwidth, in addition to the convenience of installation and the reduced sensitivity to external perturbations.
Electrical Engineering, Measurement and Control Technology