Flexible and low-cost fabrication of optical waveguides by UV laser resist-mask writing

Abstract

We report on UV laser photoresist mask writing as a tool for fabricating integrated optical waveguides and devices. Using 375 nm laser light and a pneumatically controlled direct writing stage, we defined mask features into a 250-nm-thick negative photoresist layer on a silicon nitride film on an oxidized silicon substrate. We investigated the feature size and edge roughness for different laser powers. Using the photoresist mask layer and reactive ion etching, we patterned high-refractive-index-contrast silicon nitride strip waveguides and devices with varying waveguide widths and gaps. We report on the structural and transmission characteristics of a directional coupler, Sagnac interferometer, and ring resonator and demonstrate 50/50 coupling at 1510 nm, 20 dB transmission drop at 1580 nm, and a Q factor of ∼13,000 at 1576 nm, respectively. These results demonstrate that this technique can be applied to a variety of thin film materials and substrates for inexpensive and rapid prototyping of integrated photonic devices.