In-Fiber Michelson Interferometer in Photonic Crystal Fiber for Humidity Measurement

A humidity sensor based on photonic crystal fiber (PCF) is experimentally demonstrated, which was fabricated by sandwiching a taper between PCF and a standard single mode fiber (SMF). The taper and collapsed region in PCF excite high-order modes and couple them with core mode to form a Michelson interferometer (MI). Experiment results show that the reflection interference intensity linearly changes with humidity and the sensitivity is -0.166 dB/%RH in the range of 30-90 %RH, the sensor displayed a low temperature cross-sensitivity of 0.09 %RH/°C in the temperature range of 20-100 °C. In addition, a rise/recovery time of 400/200 ms was achieved respectively for human breathing test. The easy fabrication, high sensitivity and fast response indicate the sensor has broad practical prospects.