Inverse design of broadband and lossless topological photonic crystal waveguide modes

TL;DR

This paper introduces an inverse design method for topological photonic crystal waveguides that significantly enhances bandwidth while maintaining lossless and robust edge states, using automatic differentiation and mode expansion techniques.

Contribution

It presents a fully 3D inverse design approach that doubles the bandwidth of topological waveguides, improving their practical applicability.

Findings

Bandwidth increased from 7.5% to 16.2%.

Achieved lossless, robust edge modes over a broader spectrum.

Utilized automatic differentiation for efficient inverse design.

Abstract

Topological photonic crystal waveguides can create edge states that may be more robust against fabrication disorder, and can yield propagation modes below the light line. We present a fully three-dimensional method to modify state-of-the-art designs to achieve a significant bandwidth improvement for lossless propagation. Starting from an initial design with a normalized bandwidth of 7.5% (13.4 THz), the modification gives more than 100% bandwidth improvement to 16.2% (28.0 THz). This new design is obtained using automatic differentiation enabled inverse design and a guided mode expansion technique to efficiently calculate the band structure and edge state modes.