Advanced Bragg Grating Reflectance Analysis Using FDTD for Coupled Mode Theory-Based Surrogate Models

Bragg gratings are essential components in many optical devices, including monolithic extended cavity diode lasers (mECDLs), which are designed to enhance the performance and efficiency of diode lasers [1]. This study focuses on developing accurate finite-difference time-domain (FDTD) simulations for large scale Bragg gratings by minimizing numerical errors through careful optimization of simulation parameters. A database of Bragg grating optical responses from these simulations can be used to create surrogate models. Using computationally inexpensive methods such as coupled mode theory (CMT), a 1D model, the reflectivity and shape of the reflectance spectrum can be calculated more quickly [2]. By fitting the CMT model to the simulated data, Bragg grating properties, such as the real and imaginary part of coupling coefficient, mode loss, can be determined [3]. With an accurate fitting, we can predict the reflectivity of longer Bragg gratings without time-consuming simulations, making the design process faster and more efficient.