Experimental research on FLM temperature sensor with an ethanol-filled photonic crystal fiber

• A novel optical fiber temperature sensor based on the principle of fiber loop mirror (FLM) was proposed.
• An ethanol-filled high birefringence photonic crystal fiber (HB-PCF) is inserted into the FLM as a temperature sensing element.
• Preliminary experimental results indicated that the temperature sensitivity of the two structures were 0.8833 nm/°C and 0.7896 nm/°C, respectively, for a 10 cm long HB-PCF.

A compact optical fiber temperature sensor based on the principle of fiber loop mirror (FLM) was proposed. Different from the conventional ones, an ethanol-filled high birefringence photonic crystal fiber (HB-PCF) is inserted into the FLM as a temperature sensing element. Two structures based on the FLM were designed, one is to insert a short length of ethanol-filled HB-PCF in the FLM, and the other is to make a reflective probe with the ethanol-filled HB-PCF, since the independent probe is more suitable for practical application. The refractive index of the ethanol filled in the cladding air holes of HB-PCF would change versus the applied temperature, and the birefringence of the HB-PCF would change as well, which would affect the output wavelength shifts of the FLM. Experiments were carried out to verify the sensor principle. Preliminary experimental results indicated that the temperature sensitivity of the two structures were 0.8833 nm/°C and 0.7896 nm/°C, respectively, for a 10-cm-long HB-PCF.