Nanodomain poling unlocking backward nonlinear light generation in thin film lithium niobate

TL;DR

This paper demonstrates scalable nanodomain poling in thin-film lithium niobate enabling efficient backward nonlinear light generation, including spontaneous parametric down conversion, with potential applications in quantum technologies.

Contribution

It introduces a novel scalable poling technique for x-cut TFLN with nanometer precision, enabling backward phase matching and nonlinear interactions previously unattainable.

Findings

Achieved periodic poling with periods down to 215 nm.

Demonstrated efficient sum frequency generation with high conversion efficiencies.

First report of backward propagating spontaneous parametric down conversion in TFLN.

Abstract

Nonlinear frequency conversion offers powerful capabilities for applications in telecommunications, signal processing, and computing. Thin-film lithium niobate (TFLN) has emerged as a promising integrated photonics platform due to its strong electro-optic effect and second-order nonlinearity, which can be exploited through periodic poling. However, conventional poling techniques in x-cut TFLN are limited to minimum period sizes on the order of microns, preventing the efficient generation of interactions involving counter-propagating waves. Here we report scalable periodic poling of x-cut TFLN with periods down to 215 nm and realize devices for counter- and back-propagating phase matching. We estimate conversion efficiencies of 1474 $\%$/W/cm$^2$ and 45 $\%$/W/cm$^2$ respectively, and measuring sum frequency generation we confirm that the nonlinear generation takes place in the desired direction. We report spontaneous parametric down conversion for the counter-propagating and, for the first time, for a backward propagating device. This technological advance provides the control of domain geometry in TFLN with an unprecedented precision and leads into the generation of photon pairs with spatial and spectral properties tailored for quantum signal processing, quantum computing and metrology.