Two-core Photonic Crystal Fiber with Selective Liquid Infiltration in the Central Air Hole for Temperature Sensing

A two-core photonic crystal fiber (TC-PCF) based highly-sensitive temperature sensor was proposed and demonstrated. By selectively infiltrating the central airhole with refractive index liquid (RIL), a three-parallel-waveguide structure was formed. A dual-component interference pattern, consisting of a large spectrum envelope and fine interference fringes, was observed in the transmission spectrum. The simulation results confirmed that the interference was arising from a few hybrid supermodes in the fiber coupler structure. They were in good agreement with the experimental observation on the discrete temperature windows with different temperature sensitivities due to couplings between different hybrid supermodes in respective temperature windows. By tracing the wavelength shifts of the large spectrum envelope, high sensitivities were achieved at 42.621 nm/°C in the temperature range from 54.2 °C to 55 °C and 32.159 nm/°C from 51.8 °C to 52.6 °C.