Mid-infrared broadband polarization beam splitter based on GaS photonic crystal fiber with high extinction ratio

Abstract

We design a mid-infrared polarization beam splitter (PBS) based on GaS chalcogenide dual-core photonic crystal fiber (PCF) with large bandwidth and high polarization extinction ratio (ER). The mode-coupling characteristics between the x- and y-polarized even and odd modes are investigated in the 3.5–4.5 µm range by employing the finite element method (FEM). The effects of PBS structure parameters on the coupling length (CL) and coupling length ratio (CLR) are analyzed. The results reveal that for the optimized structural parameters of a = 0.8 µm, b = 0.23 µm, d1 = 1 µm, d2 = 0.5 µm, e1 = 2.02 µm and e2 = 1.5 µm, an ultrabroad bandwidth of 412 nm (from 3.766 µm to 4.188 µm) with polarization ER better than 20 dB is achieved within an ultrashort length of 45.4 µm. The highest ER of 104 dB at the wavelength of 4 µm is obtained. The proposed PBS will become an excellent candidate for mid-infrared optical communication, optical sensing, optical precision metrology and optical nonlinearity.