Efficient transverse multi-wave interactions up to six-wave mixing in a high-Q lithium niobate microresonator

TL;DR

This paper demonstrates high-efficiency six-wave mixing in a lithium niobate microresonator using self-organized photorefractive gratings generated by stimulated Raman scattering, enabling broadband phase matching with a single CW laser.

Contribution

It introduces a novel method of achieving transverse multi-wave mixing up to six-wave in a microresonator via self-organized gratings without external lasers, advancing nonlinear photonic integration.

Findings

Achieved record 590%/W conversion efficiency for sum-frequency generation.

Demonstrated six-wave mixing with high efficiency using a single CW pump.

Enabled broadband phase matching across 500 nm spectral range.

Abstract

High-order nonlinear optical processes beyond four-wave mixing serve as fundamental tools for advancing photonic technologies, yet their practical implementation remains challenging due to stringent phase-matching requirements and inherently weak high-order nonlinear susceptibilities - limitations that persist even in state-of-the-art high-Q microresonators. In this work, we demonstrate a breakthrough in synthesizing transverse nonlinear processes up to six-wave mixing in an integrated lithium niobate microresonator, under single continuous-wave (CW) telecom-band laser pump. Our approach leverages self-organized subwavelength photorefractive gratings (SPGs) generated through bidirectional stimulated Raman scattering (SRS) process in the microresonator, without using two external counterpropagating lasers. Under 1546 nm pumping, bidirectional SRS at 1713 nm creates two counterpropagating light waves that spontaneously form SPGs. These SPGs critically enable broadband phase-matching compensation across 500 nm spectral range by providing additional momentum matching for transverse nonlinear processes while maintaining ultrahigh-Q factor. Moreover, cascaded SRS process is simultaneously activated to generate light signal for subsequent nonlinear interactions. This novel approach enables, to our knowledge, the first demonstration of single-pump phase-matched transverse sum-frequency generation (SFG) with record conversion efficiency (590%/W). Furthermore, transverse multi-wave mixing processes from four-wave to six-wave mixing processes are achieved with high conversion efficiencies for the first time using only the single CW pump, representing a notable advance in nonlinear integration.