Symmetric Second-Harmonic Generation in Sub-wavelength Periodically Poled Thin Film Lithium Niobate

TL;DR

This paper demonstrates the first reliable control of submicron ferroelectric domains in thin film lithium niobate, enabling efficient symmetric second harmonic generation with counterpropagating pumps in integrated photonics.

Contribution

It introduces a method for precise domain control in thin film lithium niobate with submicron poling periods, achieving symmetric SHG with continuous-wave pumping.

Findings

Achieved ferroelectric domain control down to 370nm in thin film lithium niobate.

Realized efficient symmetric second harmonic generation with counterpropagating pumps.

Validated the feasibility of subwavelength periodic poling on waveguides.

Abstract

Second harmonic generation (SHG) extensively employs periodically poled nonlinear crystals through forward quasi-phase-matching to achieve efficient frequency conversion. As poling periods approach sub-micrometers, backward quasi-phase-matching has also been demonstrated, albeit by utilizing pulsed laser drives. The realization of symmetric second harmonic generation, characterized by counterpropagating pumps, however, has remained elusive despite theoretical predictions. The main challenge lies in achieving strong nonlinear coupling with poling period below half the wavelength of the second-harmonic light. The recent emergence of high-quality ferroelectric lithium niobate thin films provides an opportunity for achieving precise domain control at submicron dimensions. In this article, we demonstrate reliable control of ferroelectric domains in thin film lithium niobate waveguide with a poling period down to 370nm, thereby realizing highly efficient continuous-wave pumped symmetric SHG. This demonstration not only validates the feasibility of achieving subwavelength periodic poling on waveguides but also opens new avenues for leveraging submicron ferroelectric domain structures in integrated photonics and nonlinear optics research.