We propose a mid-infrared dual-rhombic air hole hexagonal lattice photonic crystal fiber with high birefringence and large nonlinearity based on Ge 20 Sb 15 Se 65 chalcogenide glass. The properties of birefringence, dispersion, nonlinearity, and confinement loss were investigated in the 3 µm~5 µm mid-infrared range by using the Finite Difference Time Domain (FDTD) method with perfectly matched layer (PML) absorption boundary conditions. The results indicate that for the optimized structural parameters of Λ = 2.0 µm, D = 1.932 µm, d = 0.8 µm, and H = 0.8 µm, an ultrahigh birefringence of 0.041, a very low confinement loss of 0.0013 dB/km (for x -polarization modes) and 0.0342 dB/km (for y -polarization modes), and the maximum nonlinearity coefficient of 4375 w −1 km −1 (for x -polarization modes) and 3960 w −1 km −1 (for y -polarization modes) were achieved, respectively. The proposed PCF has a lower confinement loss and higher birefringence than an elliptical-hole PCF with the same air-filling fraction. Thus, it will be an excellent candidate for mid-infrared optical fiber sensing, precision optical instruments and nonlinear optics. [ABSTRACT FROM AUTHOR]