Year: 2026
Type: article
Abstract: Programmable photonic integrated circuits implement optical switching and processing by interconnecting reconfigurable 2 × 2 cells in mesh topologies. Directional couplers are widely used in these cells, often combined with phase-shifting mechanisms to enable tunability. However, conventional directional couplers in dense meshes typically require submicron gaps and tight etching tolerances, which increase sensitivity to fabrication variations and can introduce excess loss and variability. In addition, interconnected waveguides (e.g., S-bends and crossings) increase layout complexity, footprint, and bending-related penalties, while thermo-optic control may introduce power consumption and thermal crosstalk. Here, we propose a shallow-rib strip directional coupler in hydrogenated amorphous silicon (a-Si:H) for 1 µm × 1 µm multimode waveguides. The proposed geometry enables efficient coupling for waveguide separations ≥ 1 µm by shifting the coupling control from the lateral gap to the slab height, allowing smoother transitions and a relaxed fabrication flow. The analysis combines coupled-mode theory and beam propagation method simulations. As an application example, the layout of a 4 × 4 thermo-optically reconfigurable switching matrix is designed and simulated using 2 × 2 shallow-rib strip coupler cells.
Source: Photonics
Institution: Universidade Politécnica de Lisboa
Language: English
Topic: Photonic and Optical Devices
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,896
Award: G1786751596
OpenAlex ID: W7131787224