Use of Novel Periodic Multi-Layers for Highly Accurate Etch Depth Control of Ridge-Waveguide Directional Couplers

Abstract

Fabrication of large-area photonic integrated circuits (PICs) in III-V compound semiconductors presents many fabrication complexities. One difficulty is precise and reproducible etching of ridge waveguides for accurate control of optical mode shape and coupling length (distance required for full power transfer) of optical directional couplers. Directional couplers are an important element in PICs due to their utility as power taps, splitters, and combiners. However, the exponential relationship between the depth of the etched-rib waveguide and coupling length makes these structures very difficult to fabricate with precise control of coupling. This inability to precisely control the coupling purely through tight process control has led to the use of electrically biased couplers' where an electric field is applied across the waveguide to force the coupler into the desired switch state. Although biased couplers have proven successful, they are not desirable for large PICs due to the requirement of electrical contact to each coupler and careful custom tuning of the bias voltage across each coupler. In this talk, we disclose a new technique for fabrication of directional couplers with precisely controlled coupling lengths that no longer require bias-tuning after fabrication.