High Sensitivity Temperature Sensor With an Avoided-Crossing Based Selective-Filling High Birefringent Photonic Crystal Fiber Sagnac Interferometer

We proposed and demonstrated a high sensitivity temperature sensor in an avoided-crossing-based selective-filling photonic crystal fiber (SFPCF) which was designed by selectively filling two symmetrical air holes around the fiber core of an index-guiding PCF with a kind of high index liquid. The avoided-crossing effect caused by the resonant couplings rather than the crossings between the two-high-index-rod modes and the fundamental mode results in unique birefringence characteristics. The temperature response of the modal phase and group birefringence were both calculated in detail. And the phase and group birefringence are highly sensitive to temperature. Then, the transmission characteristics of a Sagnac interferometer (SI) based on the SFPCF were discussed both in theory and in experiments. The experimental results present that the weak mode couplings have no influence on the transmission spectrum of the SFPCF based SI. The interference dips at different wavelengths present distinctive transmission and temperature characteristics. In experiment, the highest temperature sensitivity of −6.9 nm/°C at 36.5°C was achieved.