FDTD Simulation of Dispersion in Photonic Crystal Fibers

FDTD (Finite-Difference Time-Domain) method is a widely used numerical approach for simulating electromagnetic wave propagation in optical devices, particularly suitable for analyzing dispersion characteristics in complex microstructured fibers like photonic crystal fibers (PCF). The improved version of the existing wang.m program optimizes the dispersion calculation process through several key enhancements: Boundary Condition Handling The periodic structure of photonic crystal fibers requires specialized boundary conditions (such as periodic boundaries or PML absorbing boundaries) to prevent unphysical reflections. The enhanced program implements dynamic boundary parameter adjustments using conditional statements to match simulation requirements across different frequency bands. Dispersion Extraction Algorithm While the original program might only use basic Fourier transforms to obtain frequency domain responses, the improved version incorporates a Group Delay calculation module. This module employs phase difference methods with numerical differentiation techniques to accurately compute effective refractive indices at different wavelengths, subsequently deriving dispersion curves through polynomial fitting algorithms. Parallelization Acceleration For large-scale PCF models, the program optimizes FDTD iteration loops using parallel computing strategies. The implementation includes spatial grid partitioning through matrix operations and potential GPU acceleration using CUDA or OpenCL frameworks, significantly reducing computation time for long-wavelength scans. Material Dispersion Compensation The traditional silica fiber material model is enhanced by embedding Sellmeier equations through additional function calls. This ensures simultaneous handling of structural dispersion and material dispersion coupling effects, improving simulation accuracy in long-wavelength regions through material property interpolation. The core value of this enhanced program lies in balancing computational efficiency with accuracy, making it suitable for studying special design requirements in PCFs such as anomalous dispersion and flat dispersion. It serves as a reliable tool for inverse design of fiber optic devices, featuring modular code structure that allows easy integration of additional physical models and parameter customization through configuration files.