Design of high nonlinear photonic crystal fiber for ultrashort pulse laser generation

Abstract This work demonstrates an optimal design for photonic crystal fiber (PCF) as a saturable absorber with high nonlinearity and low confinement losses. Using COMSOL Multiphysics 6.1 as simulation software, the propagation characteristics of the proposed PCF in terms of effective refractive index, effective mode area, chromatic dispersion, confinement loss, and nonlinearity were successfully simulated and examined in detail. A Finite Element Method (FEM) combined with a Perfectly Matched Layer (PML) absorbing boundary condition was applied to evaluate the PCF structure across a broad wavelength range from 1,000 nm to 2,000 nm. The proposed PCF features five concentric rings of air-filled holes symmetrically arranged in a hexagonal structure, with the silica core doped with a uniform level of concentration of 10 % mol of germanium (Ge). Simulation results indicate a remarkably low confinement loss at a wavelength of 1,550 nm, specifically on the order of 5 × 10 −7 (dB/m). Additionally, it reveals a high nonlinearity of 11.2 (1/W.Km) coupled with a simultaneously low negative chromatic dispersion of −14.2 (ps/nm.m). This makes it an excellent candidate for various applications involving advanced nonlinear optical systems. Such findings highlight the possibility of the proposed Ge-PCF as a promising saturable absorber for ultrashort pulse laser generation, offering a viable and practical alternative to traditional saturable absorbers in the mid-infrared region.