An ultra-broadband polarization filter and a stable temperature sensor based on a square-lattice gold-coated PCF with a different material-infiltrated core

Abstract

A simple photonic crystal fiber (PCF) arranged in a square geometry with two gold-coated air holes and one material-infiltrated core is proposed. A broadband polarization filter and a temperature sensor can be achieved based on the same simple PCF structure, with a hollow core separately filled with liquid crystal and toluene. The polarization filtering and sensing properties of the proposed PCF were studied using the finite element method (FEM). Numerically results show that variations in the diameter of both the liquid crystal-infiltrated central hole and the cladding air holes have a slight effect on the polarization filter characteristics. The polarization filter can be effectively tuned in terms of the central wavelength, crosstalk, and bandwidth by adjusting the thickness of the gold film. The proposed PCF polarization filter with t = 22.5 nm has achieved a wide bandwidth of 1850 nm across wavelengths ranging from 1.2 to 3.05 μm for a fiber length of 50 μm, achieving a high value of polarization loss ratio (PLR) of 28,717 at λ = 1.31 μm with losses of 1723 dB/cm for y-polarization and 0.06 dB/cm for x-polarization. The y-polarized core mode in this design with t = 10 nm is rapidly attenuated, experiencing losses larger than 1340 dB/cm over wavelengths ranging from 1.9 to 3.0 μm; it also exhibits a bandwidth of 2200 nm with crosstalk greater than 20 dB when using a fiber length of 50 μm at wavelengths above 1.5 μm. Furthermore, a temperature sensor that utilizes toluene as its core material exhibits a consistent average sensitivity of 6.68 nm/°C for y-polarization and can detect temperatures ranging from − 10 to 40 °C. The sensor maintains stable sensitivity within ± 1% fluctuation of the gold film thickness in the sensing range of − 10 to 40 °C.