# Optical isolation with nonlinear topological photonics

## TL;DR

This paper demonstrates how topological phase transitions in nonlinear photonic structures can be harnessed to create optical isolators with power thresholds and sharp transmittance discontinuities, advancing nonlinear topological photonics.

## Contribution

It introduces novel designs of nonlinear photonic structures utilizing topological transitions for optical isolation, including 1D and 2D waveguide arrays and coupled-ring lattices.

## Key findings

- Topological transitions correlate with power thresholds in transmittance.
- Self-induced topological solitons emerge at transition points.
- Discontinuities in transmittance enable sharp power-dependent isolation.

## Abstract

It is shown that the concept of topological phase transitions can be used to design nonlinear photonic structures exhibiting power thresholds and discontinuities in their transmittance. This provides a novel route to devising nonlinear optical isolators. We study three representative designs: (i) a waveguide array implementing a nonlinear 1D Su-Schrieffer-Heeger (SSH) model, (ii) a waveguide array implementing a nonlinear 2D Haldane model, and (iii) a 2D lattice of coupled-ring waveguides. In the first two cases, we find a correspondence between the topological transition of the underlying linear lattice and the power threshold of the transmittance, and show that the transmission behavior is attributable to the emergence of a self-induced topological soliton. In the third case, we show that the topological transition produces a discontinuity in the transmittance curve, which can be exploited to achieve sharp jumps in the power-dependent isolation ratio.