Phase matched second harmonic generation in an on-chip lithium niobate microresonator fabricated by femtosecond laser

TL;DR

This paper demonstrates efficient second harmonic generation in an on-chip lithium niobate microresonator by overcoming phase matching challenges through selective mode excitation, advancing integrated nonlinear photonics.

Contribution

It introduces a femtosecond laser fabrication method for lithium niobate microresonators that achieve phase matched SHG by mode selection, enabling improved on-chip nonlinear optics.

Findings

High SHG efficiency achieved in on-chip lithium niobate microresonator.

Selective excitation of high order modes overcomes phase matching issues.

Potential for integrated classical and quantum photonic devices.

Abstract

Nonlinear optical processes in whispering gallery mode (WGM) microresonators have attracted much attention. Owing to the strong confinement of light in a small volume, a WGM microresonator can dramatically boost the strength of light field, thereby promoting the nonlinear interaction between the light and the resonator material. However, realization of efficient nonlinear parametric process in microresonators is a challenging issue. The major difficulty is to simultaneously ensure the phase matching condition and a coherent multiple resonance condition for all the waves participating in the nonlinear conversion process. Here, we demonstrate highly efficient second harmonic generation (SHG) in an on-chip lithium niobate microresonator fabricated by femtosecond laser direct writing. We overcome the difficulty of double resonance for the phase matched pump and second harmonic waves by selectively exciting high order modes in the fabricated thin-disk microresonator. Our technique opens opportunities for integrated classical and quantum photonic applications.