High-order harmonic generation in uniformly distributed topological edge states

Abstract

Second-harmonic generation and third-harmonic generation have been widely investigated in nonlinear topological photonics. However, due to the weak nonlinear effect and the strict phase matching condition, it is a challenge to observe the high-order harmonic generation in general bulky or periodic structures. In this work, through the design of a binary one-dimensional photonic crystal, we obtain the topological edge states (TESs) with equal frequency spacing based on the electro-optic modulation effect. The designed structure has generated the high-order harmonic waves with the nonlinear effect excited by intense femtosecond laser pulses. The uniformly distributed TESs satisfy the request of phase matching. The nonlinear sum-frequency effect combined with the unique TESs leads to high-order harmonic waves. The presented work provides a feasible scheme to generate the high-order harmonic waves from the simple 1D structure.