Broadband nonlinear optical microresonator array for topological second harmonic generation

TL;DR

This paper introduces a broadband topological nonlinear photonic system using a 2D microresonator array with engineered bandgaps, enabling efficient second-harmonic generation with robust, flux-programmable chirality and significantly improved efficiency.

Contribution

It presents a novel design of a 2D microresonator array with dual topological bandgap engineering for broadband, efficient, and robust topological second-harmonic generation.

Findings

Achieves topological phase matching with unidirectional edge states for pump and SH frequencies.

Demonstrates flux-programmable SH chirality with propagation reversal via Chern number transitions.

Yields over 100 times higher SHG efficiency than single resonators at high powers.

Abstract

Topological photonics enables robust light manipulation with third-order optical nonlinearity, yet integrating second-order optical nonlinearity into a topological system faces fundamental challenges: frequency-dependent topological bandgaps impede simultaneous edge states for pump and second harmonic photons at an octave. Here we present a broadband topological nonlinear photonic system via dual frequency topological bandgap engineering in a 2D nonlinear microresonator array. By designing a square lattice with synthetic magnetic fluxes, we achieve topological phase matching preserving unidirectional edge states for both frequencies while enabling efficient second-harmonic generation. The system exhibits flux-programmable SH chirality, where SH photons reverse propagation direction via Chern number transitions (e.g. C = -1 to +1) without sacrificing robustness. Moreover, we show that the design theoretically yields over 100 times higher SHG efficiency than single resonators at high powers via topology-enhanced coherent buildup. Our topological SHG works in a parameter regime that can be readily accessed by using existing low-loss integrated photon platforms like thin film lithium niobite.