Apodizer Design to Efficiently Couple Light into a Fiber Bragg Grating

TL;DR

This paper develops an optimal control framework and uses genetic algorithms to design fiber Bragg gratings that maximize light coupling efficiency and slow light propagation, enhancing nonlinear optical device performance.

Contribution

It introduces a novel combination of optimal control and genetic algorithms to optimize fiber Bragg grating designs, including the use of grating chirp, for improved light coupling and slow light generation.

Findings

Optimized grating structures increase light coupling efficiency.

Designed gratings produce slower propagating pulses.

Inclusion of chirp parameter enhances design space exploration.

Abstract

We provide an optimal control framework for efficiently coupling light in a bare fiber into Bragg gratings with a cubic nonlinearity. The light-grating interaction excites gap solitons, a type of localized nonlinear coherent state which propagates with a central frequency in the forbidden band gap, resulting in a dramatically slower group velocity. Due to the nature of the band gap, a substantial amount of light is back-reflected by the grating's strong reflective properties. We optimize, via a projected gradient descent method, the transmission efficiency of previously designed nonuniform grating structures in order to couple more slow light into the grating. We further explore the space of possible grating designs, using genetic algorithms, along with a previously unexplored design parameter: the grating chirp. Through these methods, we find structures that couple a greater fraction of light into the grating with the added bonus of creating slower pulses.