Towards nanophotonic optical isolation via inverse design of energy transfer in non-reciprocal media

TL;DR

This paper extends inverse design methods to non-reciprocal media, enabling optimized one-way energy transfer for nanophotonic optical isolation using a novel adjoint approach and topology optimization.

Contribution

It introduces the 'Faraday-adjoint' method for shape optimization in magneto-optical media and derives a general energy transfer equation for nonreciprocal systems.

Findings

Successful optimization of one-way energy transfer in 3D nonreciprocal media

Development of a generalized Born series for tensor permittivity

Establishment of a framework for practical nanophotonic isolation

Abstract

In this work we generalise the adjoint method of inverse design to nonreciprocal media. As a test case, we use three-dimensional topology optimization via the level-set method to optimise one-way energy transfer for point-like source and observation points. To achieve this we introduce a suite of tools, chiefly what we term the `Faraday-adjoint' method which allows for efficient shape optimization in the presence of magneto-optical media. We carry out an optimization based on a very general equation that we derive for energy transfer in a nonreciprocal medium, and link finite-different time-domain numerics to analytics via a modified Born series generalised to a tensor permittivity. This work represents a stepping stone towards practical nanophotonic optical isolation, often regarded as the `holy grail' of integrated photonics.