Inverse Design of Compact Multimode Cavity Couplers

TL;DR

This paper introduces an adjoint optimization method for designing compact, broadband, multi-wavelength waveguide-cavity couplers in silicon photonics, enabling efficient multi-mode coupling in integrated optical devices.

Contribution

It presents a systematic large-scale optimization approach for designing wavelength-scale couplers that control multi-mode interactions over broad frequency bands.

Findings

Achieved critical coupling at up to six wavelengths spanning 560-1500 nm.

Demonstrated couplers for multi-ring cavities with tunable broadband performance.

Validated the design method through numerical simulations.

Abstract

Efficient coupling between on-chip sources and cavities plays a key role in silicon photonics. However, despite the importance of this basic functionality, there are few systematic design tools to simultaneously control coupling between multiple modes in a compact resonator and a single waveguide. Here, we propose a large-scale adjoint optimization approach to produce wavelength-scale waveguide--cavity couplers operating over tunable and broad frequency bands. We numerically demonstrate couplers discovered by this method that can achieve critical, or nearly critical, coupling between multi-ring cavities and a single waveguide at up to six widely separated wavelengths spanning the $560$--$1500$~nm range of interest for on-chip nonlinear optical devices.