Integrated Passive Nonlinear Optical Isolators

TL;DR

This paper presents a passive, integrated optical isolator using Kerr nonlinearity in silicon nitride ring resonators, achieving significant isolation without magneto-optic materials or high-frequency modulation.

Contribution

It introduces a novel passive on-chip optical isolator based on Kerr nonlinearity, enabling effective laser stabilization without complex modulation or magnetic materials.

Findings

Single ring isolation of 17-23dB with low insertion loss

Cascaded rings achieve 35dB isolation

Successful hybrid integration with semiconductor laser

Abstract

Fiber and bulk-optical isolators are widely used to stabilize laser cavities by preventing unwanted feedback. However, their integrated counterparts have been slow to be adopted. While several strategies for on-chip optical isolation have been realized, these rely on either integration of magneto-optic materials or high frequency modulation with acousto-optic or electro-optic modulators. Here, we demonstrate an integrated approach for passively isolating a continuous wave laser using the intrinsically non-reciprocal Kerr nonlinearity in ring resonators. Using silicon nitride as a model platform, we achieve single ring isolation of 17-23dB with 1.8-5.5dB insertion loss, and a cascaded ring isolation of 35dB with 5dB insertion loss. Employing these devices, we demonstrate hybrid integration and isolation with a semi-conductor laser chip.