Inverse-Designed Non-Hermitian Hollow Nanowire Cavity for Generating Optical Orbital Angular Momentum

TL;DR

This paper presents an inverse-designed gallium nitride hollow nanowire cavity that efficiently generates high-purity optical orbital angular momentum within a compact, single-component device.

Contribution

It introduces a novel non-Hermitian nanowire cavity design optimized via inverse methods to produce high-order OAM with high purity and Q-factor in a minimal footprint.

Findings

Achieved a mode with |l| = 5.7 OAM with 97% purity.

Realized a cavity with a Q-factor of approximately 250.

First sub-micron active device capable of generating high-order optical OAM.

Abstract

We designed a gallium nitride hexagonal hollow nanowire whispering gallery mode cavity that generates an |m|=6 topological light with orbital angular momentum (OAM). OAM is generated by breaking the cross-sectional mirror symmetry of the nanowire, which creates a non-Hermitian system. This is achieved by replacing the central airhole of the hollow nanowire with a cluster of 6 overlapping circular air holes with rotational offset relative to the hexagonal cross-sectional profile of the nanowire. The design parameters were then further optimized in Finite Element Method using an inverse design method to maximize the normalized OAM order |l|. We were able to realize of a cavity mode with |l| = 5.7, a mode purity of about 97%, and a Q-factor of ~250. This marks the first OAM generating active photonic device design falling within a sub-micron footprint, with additional novelties of being single component and materialistically homogeneous.