Characteristics of Dielectric-clad Directional Couplers for Improved Edge Coupling to Hybrid Detectors

Abstract

Active components on glass and lithium niobate substrates have been fabricated by combining passive waveguides with an overlay of grafted semiconductor material for optical detection applications1. To improve the overall coupling from an optical fiber to the detector, a vertical directional coupler that transfers power from a buried waveguide (with a minimal insertion loss) to a surface waveguide was recently proposed and demonstrated using a field- assisted K+-ion exchange in glass2. Though this scheme works well for vertical coupling of light to the detector, its efficiency is impaired by the presence of a thin layer of low index amorphous material at the semiconductor/waveguide bonding interface3. An effective way to avoid this problem is to use edge coupling to the detector which can be achieved by cladding the waveguide/detector structure with a dielectric thin film of refractive index higher than that of the waveguide4. Here, we report preliminary results on the fabrication and measurement of a vertical directional coupler that is clad with a sputtered Corning 7059 glass thin film to take advantage of this edge coupling scheme. In addition, we compare the experimental to the theoretical results obtained using a finite-difference vector beam propagation method5 (FD-VBPM).