Low-loss broadband bi-layer edge couplers for visible light

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Visible-light photonic-integrated circuits (PICs) face challenges in achieving low-loss broadband fiber-to-chip coupling.
• High confinement waveguides are needed for dense integration, but minimum feature sizes are limited by foundry lithography.

Purpose of the Study:

• To demonstrate a novel bi-layer silicon nitride (SiN) edge coupler design for efficient fiber-to-chip coupling in visible-light PICs.
• To overcome the trade-off between waveguide confinement and lithographical limits.

Main Methods:

• Fabrication of bi-layer SiN edge couplers.
• Characterization of coupling loss with Nufern S405-XP fiber across a 445-640 nm wavelength range.
• Mode analysis and adiabatic mode transfer simulation.

Main Results:

• Achieved coupling loss of ≤4 dB/facet over the 445-640 nm broadband spectrum.
• Utilized a thin SiN layer to expand the mode at the fiber facet for adiabatic transfer.
• Maintained a minimum lithographic feature size of 150 nm.
• Demonstrated 3-5 dB lower coupling loss compared to single-layer designs.

Conclusions:

• The bi-layer SiN edge coupler design offers a significant improvement in fiber-to-chip coupling for visible-light PICs.
• This approach enables high-density integration by allowing high-confinement waveguides within foundry limitations.
• The broadband performance makes it suitable for various visible-light photonic applications.