Fiber Sagnac interferometer based on a liquid-filled photonic crystal fiber for temperature sensing

•The phase birefringence B, the group birefringence Bg, and the sensitivity dependence on the operable wavelength are analyzed which is helpful to study other fiber sensors.•The birefringence sensitive coefficient of ∂B/∂T∂B/∂T is about −10−7/°C.•The sensitivity is −11.9 nm/°C (−29 750 nm/RIU) at 1.8 μm as the temperature is 25 °C.•The average sensitivity could reach to −7.54 nm/°C (−18 850 nm/RIU), the temperature varies from 25 °C to 85 °C, and the linearity is 0.98211.

A fiber Sagnac interferometer based on the square-lattice photonic crystal fiber (PCF) for temperature sensing is designed. All the air holes are assumed to be filled with temperature sensitive liquid. The temperature sensing characteristics are analyzed by finite element method (FEM). The phase birefringence B, the group birefringence Bg, and the sensitivity dependence on the operable wavelength λ are studied, and the temperature varies from 25 °C to 85 °C. The birefringence sensitive coefficient of ∂B/∂T∂B/∂T is −10−7/°C−10−7/°C. The sensitivity could reach to −11.9 nm/°C (−29 750 nm/RIU) at 1.8 μm as the temperature is 25 °C. The sensitivity is also studied by the transmission spectrum, and the wavelength spacing between the resonance wavelengths at 85 °C can reach to 492 nm. The average sensitivity could reach to −7.54 nm/°C (−18 850 nm/RIU). The diameter d1 on the sensing characteristics of the temperature sensor is also analyzed. The temperature sensor shows high sensitivity and broad detecting window.