Single-polarization single-mode photonic crystal fiber based on Sierpiński gasket without holes in the cladding

A photonic crystal fiber without any hole in the cladding is designed to achieve single-polarization single-mode (SPSM) operation. The core of PCF consists of alternating silicon nitride cylinders and air holes. Based on the full vector finite element method (FEM), characteristics of guiding modes are studied. The simulation results indicate that the proposed PCF offers an SPSM bandwidth of 241 nm (1.447~1.688 μm). At the center wavelength of 1.55 μm, the optimal structure realizes a high birefringence of 9.71×10^-3, a negative dispersion of -601.6 ps/(km·nm), an extremely low confinement loss of 7.77×10^-6 dB/km, and a high nonlinearity coefficient of 130.4 W^-1·km^-1. The proposed structure presents extensive application prospects in areas of polarization modulation, optical fiber sensing, ultra-short laser systems, etc.