Lithium niobate waveguides with high-index contrast and preserved nonlinearity fabricated by High Vacuum Vapor-phase Proton Exchange

TL;DR

This paper introduces a novel High Vacuum Vapor-phase Proton Exchange process for fabricating lithium niobate waveguides that achieve high index contrast and low losses without degrading nonlinearity, suitable for integrated nonlinear photonics.

Contribution

The paper presents a new fabrication method, HiVac-VPE, that maintains nonlinearity and reduces losses in lithium niobate waveguides with high index contrast.

Findings

Waveguides exhibit high index contrast and low propagation losses.

Nonlinear response, including SHG, is preserved in fabricated waveguides.

Index profiles reveal sub-layer structures depending on exchange duration.

Abstract

Highly confining waveguides without degraded nonlinear coefficient and low propagation losses have been fabricated in lithium niobate by a new process that we called High Vacuum Vapor-phase Proton Exchange (HiVac-VPE). Index contrast, index profile, nonlinearity and crystallographic phases are carefully investigated. Original analysis of index profiles indicates that the waveguides contains sub-layers whose depths are depending on the exchange durations. Propagation behavior, propagation losses and Second Harmonic Generation (SHG) response of HiVac-VPE channel waveguides are investigated at telecom wavelength. The results recommend HiVac-VPE as very promising technique for fabricating efficient nonlinear photonic integrated circuits in LN crystals.