Stimulated Brillouin scattering in optimized photonic crystal fiber to achieve high Brillouin gain coefficient

Solid core silica photonic crystals fibers (PCFs) were designed with different pitches and hole diameters. This design aims to perform numerical simulation of backscattered stimulated Brillouin scattering in these fibers and calculate the stimulated Brillouin gain coefficient. Stimulated Brillouin gain scattering has potential applications such as sensing, laser technology, microwave photonics, delay, storage and processing of optical information. All of these applications require a high Brillouin gain coefficient. The goal is to optimize the PCF design parameters to achieve a very high gain coefficient considering the pump wavelength of 1.55 μm (optical communication window). A very high gain coefficient of 5 m⁻¹ W⁻¹ has been achieved in a PCF with a pitch, Λ = 1.83 μm and an air hole diameter, d = 1.65 μm. COMSOL Multiphysics software was used to calculate the Brillouin shift, the effective mode index of the optical field, the acoustic mode sound velocity, the frequency-wave vector curve, and the stimulated gain coefficient for different PCFs. The acoustic frequency vs. wave vector curve has been used to calculate the acoustic wave speed. Due to the law of conservation of momentum, the vector of the acoustic wave is equal to twice the propagation vector of the optical mode. The corresponding acoustic angular frequency divided by this acoustic wave vector gives the speed of sound. In calculating the stimulated gain coefficient, all the important effects such as the photoelastic effect, the moving boundary condition, electrostriction, and radiation pressure have been considered in the simulation.