Phenomenon in an alcohol not full-filled temperature sensor based on an optical fiber Sagnac interferometer.

An alcohol not full-filled high-birefringence photonic crystal fiber (HiBi-PCF) temperature sensor based on an optical fiber Sagnac interferometer (OFSI) is demonstrated and investigated in detail. A new phenomenon that the resonant dip wavelengths of the temperature sensor blueshift with temperature increasing is observed, which is contrary to that of the previously reported alcohol filled HiBi-PCF OFSI temperature sensor. By considering the influences of the group birefringence and the thermo expansion of alcohol, this phenomenon is explained very well. The temperature sensitivity of the proposed sensor is about -1.17 nm/°C and is only one-sixth of that of the alcohol full-filled HiBi-PCF OSFI.