Ultra-smooth LiNbO3 micro and nano structures for photonic applications

Gwenn Ulliac,Blandine Guichardaz,Jean-Yves Rauch,Samuel Queste,Sarah Benchabane,Nadège Courjal

doi:10.1016/j.mee.2011.02.024

Abstract

We report on two approaches to achieve ultra-smooth structures on lithium niobate (LiNbO3) substrates. The first method relies on ICP-RIE (inductively coupled-reactive ionic etching) or on RIE, and is exploited here for the fabrication of rods with smooth etched surfaces. A series of tests have been performed with fluorine gases. Nanometric rods with 200, 400 or 600nm diameters, with a periodicity of 400, 800 and 1200nm respectively and etched angles close to 68° for the RIE process and 75° for the ICP-RIE process have been fabricated. The second process is based on “optical grade dicing” and is dedicated to the fabrication of deep-etched ridge waveguides. First optical characterization results are reported. They show optical propagation losses value close to 0.1dB/cm.

Highlights

Structuring LiNbO3 for photonic applications has been attracting much attention during the last 10 years owing to the potentialities offered by this material in terms of electro-optical, acousto-optical or nonlinear interactions and requires anisotropic etching for various devices
We present two methods which can lead to ultra-smooth LiNbO3 micro and nano structures
We demonstrate here that nanometric rods surrounded with smoothed etch surfaces can be obtained by properly choosing the dry etching conditions, and by preliminarily realizing a proton exchange step (PE)

Summary

Introduction

Structuring LiNbO3 for photonic applications has been attracting much attention during the last 10 years owing to the potentialities offered by this material in terms of electro-optical, acousto-optical or nonlinear interactions and requires anisotropic etching for various devices. Batch methods based on wet etching have been studied: many works have shown the capability of HF acids for etching LiNbO3 substrates [3,4,5]. Techniques based on dry etching such as RIE, ICP-RIE, or NLD (neutral loop discharge) have been proposed for the fabrication of photonic structures [6,7] or ridges [8]. None of these publications report on the possibility to obtain ultra-smooth structures on lithium niobate substrates. The second one is based on ‘‘optical grade dicing’’ and is dedicated to the fabrication of optical deep-etched ridge waveguides

Fabrication of nanometric rods with dry etching techniques

Cr removal by wet etching cleaning

Fabrication of optical ridge waveguides with optical grade dicing method

Conclusions