Second-Harmonic Generation in Etchless Lithium Niobate Nanophotonic Waveguides with Bound States in the Continuum

TL;DR

This paper demonstrates efficient second-harmonic generation in etchless lithium niobate nanophotonic waveguides using bound states in the continuum, enabling low-loss, thermally stable nonlinear optical processes on a cost-effective platform.

Contribution

It presents the first experimental use of photonic BICs for second-harmonic generation in etchless lithium niobate waveguides, advancing integrated nonlinear photonics.

Findings

Achieved 0.175%W-1cm-2 conversion efficiency.

Demonstrated thermal stability with only 1.7 nm wavelength shift from 25°C to 100°C.

Enabled efficient nonlinear processes on a cost-effective, etchless platform.

Abstract

Bound states in the continuum (BICs) have been extensively studied in various systems since its first proposal in quantum mechanics. Photonic BICs can enable optical mode confinement and provide field enhancement for nonlinear optics, but they have rarely been explored in nonlinear integrated photonic waveguides. Applying BICs in photonic integrated circuits enables low-loss light guidance and routing in low-refractive-index waveguides on high-refractive-index substrates, which is suitable for integrated photonics with nonlinear materials. Here, we report experimental demonstration of second-harmonic generation from telecom to near-visible wavelengths on an etchless lithium niobate platform by using a photonic BIC for the second-harmonic mode. The devices feature second-harmonic conversion efficiency of 0.175%W-1cm-2 and excellent thermal stability with a wavelength shift of only 1.7 nm from 25{\deg}C to 100{\deg}C. Our results represent a new paradigm of nonlinear integrated photonics on a cost-effective and convenient platform, which can enable a broad range of on-chip applications such as optical parametric generation, signal processing, and quantum photonics.