Second harmonic and cascaded third harmonic generation in generalized quasi-periodic poled lithium niobate waveguides

TL;DR

This paper demonstrates efficient second- and cascaded third-harmonic generation in generalized quasi-periodic poled lithium niobate waveguides fabricated on thin film, highlighting their potential for nonlinear integrated photonics.

Contribution

First fabrication of LNOI ridge waveguides with generalized quasi-periodic poled superlattices enabling efficient harmonic generation.

Findings

Normalized conversion efficiency for SHG is 1735% W$^{-1}$cm$^{-2}$

Cascaded THG efficiency is 0.41% W$^{-2}$cm$^{-4}$

Efficient harmonic signals observed in the same device

Abstract

Lithium niobate (LN) thin film has recently emerged as an important platform for nonlinear optical investigations for its large $\chi^{(2)}$ nonlinear coefficients and ability of light localization. In this paper, we report the first fabrication of LN on insulator (LNOI) ridge waveguides with generalized quasi-periodic poled superlattices using the electric field polarization technique and microfabrication techniques. Benefiting from the abundant reciprocal vectors, we observed efficient second-harmonic and cascaded third-harmonic signals in the same device, with the normalized conversion efficiency 1735% W$^{-1}$cm$^{-2}$ and 0.41% W$^{-2}$cm$^{-4}$, respectively. This work opens a new direction of nonlinear integrated photonics based on LN thin film.