Low-loss fiber-to-chip edge coupler for silicon nitride integrated circuits

Area of Science:

• Photonics and Materials Science
• Integrated Optics and Waveguide Technology

Background:

• Silicon nitride (SiN) waveguides offer excellent optical properties like low loss and high nonlinearity.
• A significant challenge in SiN integrated photonics is efficient fiber coupling due to mode mismatch.

Purpose of the Study:

• To propose and demonstrate a novel coupling strategy for SiN waveguides.
• To improve fiber-to-waveguide coupling efficiency and tolerance.

Main Methods:

• Utilized a high-index doped silica glass (HDSG) waveguide as a mode transition intermediary.
• Fabricated and characterized the HDSG intermediary and SiN waveguide structures.
• Measured coupling efficiency across C and L telecommunication bands.

Main Results:

• Achieved fiber-to-SiN waveguide coupling efficiency below 0.8 dB/facet.
• Demonstrated high fabrication and alignment tolerances for the proposed coupling method.
• Successful broadband coupling across the full C and L bands.

Conclusions:

• The HDSG intermediary effectively smooths mode transitions for improved fiber coupling.
• This method offers a practical solution for efficient light injection into SiN photonic integrated circuits.
• The approach enhances the usability of SiN waveguides in various optical applications.