Basic structures for photonic integrated circuits in Silicon-on-insulator

TLDR

Compact photonic circuits require wavelength‑scale, high‑index‑contrast structures. The study aims to improve fiber coupling by developing vertical couplers with >21 % efficiency. Using deep‑UV CMOS lithography, we fabricated silicon‑on‑insulator nanophotonic wires, crystal waveguides, and vertical couplers. Fabricated photonic wires exhibit 0.24 dB/mm loss versus 7.5 dB/mm for crystal waveguides, while vertical couplers achieve >21 % efficiency and spot‑size converters >70 % mode‑to‑mode coupling.

Abstract

For the compact integration of photonic circuits, wavelength-scale structures with a high index contrast are a key requirement. We developed a fabrication process for these nanophotonic structures in Silicon-on-insulator using CMOS processing techniques based on deep UV lithography. We have fabricated both photonic wires and photonic crystal waveguides and show that, with the same fabrication technique, photonic wires have much less propagation loss than photonic crystal waveguides. Measurements show losses of 0.24dB/mm for photonic wires, and 7.5dB/mm for photonic crystal waveguides. To tackle the coupling to fiber, we studied and fabricated vertical fiber couplers with coupling efficiencies of over 21%. In addition, we demonstrate integrated compact spot-size converters with a mode-to-mode coupling efficiency of over 70%.