Electro-Optically Tunable ${\rm As}_{2}{\rm S}_{3}$ Mach–Zehnder Interferometer on ${\rm LiNbO}_{3}$ Substrate

An electro-optically tunable vertically integrated As₂S₃ Mach-Zehnder interferometer side coupled to a Ti-diffused waveguide on LiNbO₃ substrate was designed and fabricated. Asymmetric coplanar strip electrodes were placed along the As₂S₃ path, which show strong electro-optic tuning capability, shifting the FSR of the interferometer. The tuning of the TM polarization with 7-mm-long electrodes having a 7-μm gap was observed with V_πL = 15.9 V-cm, giving a tuning rate of 0.028 nm/V at 1530 nm. To our knowledge, this is the first demonstration of electro-optic tuning of an As₂S₃ guided mode on LiNbO₃ substrate.

I. Introduction

Lithium niobate has long been a substrate of choice for optical devices due to the ability to electro-optically tune the refractive index of the substrate. While exhibits excellent electro-optic properties, one problem is that standard titanium diffused waveguides are limited in their bending radii. Tunable microring resonators have been realized with waveguides, but substrate wet etching is necessary prior to diffusion to create a ridge waveguide structure [1]. To avoid substrate etching, a hybrid on platform can be used to obtain tight bending radii. Chalcogenide glasses such as arsenic trisulfide have a large refractive index, allowing for tight bending radii and the fabrication of low-loss, high-Q ring resonators [2].