Enhanced sensitivity of temperature sensor by a PCF with a defect core based on Sagnac interferometer

•The sensitivities can reach to 79.2 nm/°C and −69.9 nm/°C as the temperature is 23°C.•The high sensitivities are 77,000 nm/RIU and −106,000 nm/RIU as the RI of the liquid is 1.409.•The sensitivity increases infinitely near the special wavelength related with zero-point group birefringence Bg.•The wavelength of zero-point group birefringence Bg can be changed by adjusting the corresponding parameters.

We propose a high-sensitivity temperature sensor based on Sagnac interferometer with a PCF. The diameter of the central hole of the PCF is decreased to form defect core which supports fiber mode. All the air holes are injected with liquid which is sensitive to temperature. The simulation result demonstrates that the birefringence of the PCF is low. The loss, the overlap between fiber mode and the liquid in the central hole increases as the wavelength increases. The sensitivity has a great relation with group birefringence Bg. Therefore, we analyze the influences of the structural parameters d1, d2, d3 and the RI of the liquid on the group birefringence Bg. By adjusting the corresponding parameters, we can change the wavelength of zero-point group birefringence Bg. The high sensitivity can be obtained near the special wavelength. The sensitivities can reach to 79.2 nm/°C and −69.9 nm/°C as the temperature is 23 °C. The average sensitivities are 26.4 nm/°C, −17.9 nm/°C as the temperature changes from 27 °C to 35 °C, and the linear fitting degrees are 0.99489 and 0.98832. The RI sensitivity is also studied as RI changes from 1.404 to 1.409. The average sensitivities are 43,400 nm/RIU and −73,743 nm/RIU respectively. The high sensitivities are 77,000 nm/RIU and −106,000 nm/RIU as the RI of the liquid is 1.409.