Unidirectional lasing in nonlinear Taiji micro-ring resonators

TL;DR

This paper introduces a formalism for unidirectional lasing in nonlinear Taiji micro-ring resonators, demonstrating how device geometry and Kerr nonlinearity enable stable, non-reciprocal laser emission without magnetic components.

Contribution

The work presents a new theoretical framework for unidirectional lasing in Taiji micro-ring resonators, highlighting the role of device geometry and nonlinearity in mode selection.

Findings

Unidirectional lasing achieved in Taiji resonators with S-shaped waveguides.

Kerr nonlinearity enhances mode selection and stability.

Device geometry breaks time-reversal symmetry dynamically.

Abstract

We develop a general formalism to study laser operation in active micro-ring resonators supporting two counterpropagating modes. Our formalism is based on the coupled-mode equations of motion for the field amplitudes in the two counterpropagating modes and a linearized analysis of the small perturbations around the steady state. We show that the devices including an additional S-shaped waveguide establishing an unidirectional coupling between both modes -- the so-called Taiji resonators (TJR) -- feature a preferred chirality on the laser emission and can ultimately lead to unidirectional lasing even in the presence of sizable backscattering. The efficiency of this mode selection process is further reinforced by the Kerr nonlinearity of the material. This stable unidirectional laser operation can be seen as an effective breaking of $\mathcal{T}$-reversal symmetry dynamically induced by the breaking of the $\mathcal{P}$-symmetry of the underlying device geometry. This mechanism appears as a promising building block to ensure non-reciprocal behaviors in integrated photonic networks and topological lasers without the need for magnetic elements.