Midinfrared high birefringence Ge20Sb15Se65-based photonic crystal fiber with large nonlinearity using dual-rhombic air hole

A midinfrared high birefringence Ge20Sb15Se65-based hexagonal lattice photonic crystal fiber (PCF) with central defect core and dual-rhombic air holes cladding is proposed. The finite difference time-domain method with perfectly matched layer absorption boundary conditions are used to numerically analyze the guided modes of the designed PCF. The properties of this PCF including the birefringence, beat length, dispersion, and nonlinearity are investigated in the 3 to 5  μm midinfrared range. The results show that for the optimized structure parameters of Λ  =  2  μm, D  =  1.7  μm, H  =  1.76, and d  =  0.4  μm, the highest birefringence of 0.1513 and beat length of 33.04  μm are obtained. The maximum nonlinearity coefficients of 3726 and 2585  w  −  1 km  −  1 for x- and y-polarization modes are achieved. The distinctive dispersion is acquired, which is all-normal for x-polarization mode while has single zero dispersion points at 3.96  μm for y-polarization mode. The designed PCF will have broad application in midinfrared optical fiber sensing, nonlinear optics, and precision optical instruments.