Complete linear optical isolation at the microscale with ultralow loss

TL;DR

This paper demonstrates a magnet-free, chip-scale optical isolator using a whispering-gallery microresonator and Brillouin scattering, achieving ideal linear optical isolation with ultralow loss suitable for integrated photonics.

Contribution

It introduces a novel, material-agnostic method for linear optical isolation based on nonreciprocal induced transparency via coherent light-sound interaction.

Findings

Achieves complete linear optical isolation with ultralow forward loss.

Utilizes nonreciprocal induced transparency from Brillouin scattering.

Compatible with standard photonic waveguide materials.

Abstract

Low-loss optical isolators and circulators are critical nonreciprocal components for signal routing and protection, but their chip-scale integration is not yet practical using standard photonics foundry processes. The significant challenges that confront integration of magneto-optic nonreciprocal systems on chip have made imperative the exploration of magnet free alternatives. However, none of these approaches have yet demonstrated linear optical isolation with ideal characteristics over a microscale footprint - simultaneously incorporating large contrast with ultralow forward loss - having fundamental compatibility with photonic integration in standard waveguide materials. Here we demonstrate that complete linear optical isolation can be obtained within any dielectric waveguide using only a whispering-gallery microresonator pumped by a single-frequency laser. The isolation originates from a nonreciprocal induced transparency based on a coherent light-sound interaction, with the coupling originating from the traveling-wave Brillouin scattering interaction, that breaks time-reversal symmetry within the waveguide-resonator system. Our result demonstrates that material-agnostic and wavelength-agnostic optical isolation is far more accessible for chip-scale photonics than previously thought.