High-Efficiency Metamaterial-Engineered Grating Couplers for Silicon Nitride Photonics

Area of Science:

• Photonics
• Materials Science
• Integrated Optics

Background:

• Silicon nitride (Si3N4) is crucial for low-loss photonic integrated circuits.
• Efficient light coupling between optical fibers and Si3N4 chips is a major challenge.
• Existing vertical grating couplers have limitations due to low index contrast and long structures.

Purpose of the Study:

• To design high-efficiency surface grating couplers for Si3N4 photonic platforms.
• To enhance fiber-chip coupling performance using amorphous silicon (α-Si) overlays.
• To leverage subwavelength grating (SWG) metamaterials for improved coupler design.

Main Methods:

• Design of surface grating couplers using an α-Si overlay on a Si3N4 platform.
• Utilizing subwavelength grating (SWG) engineered metamaterials for grating fabrication.
• Employing rigorous 3D finite-difference time-domain (FDTD) simulations for performance analysis.

Main Results:

• A metamaterial-engineered grating coupler was designed with a coupling efficiency of -1.7 dB.
• The coupler operates at a wavelength of 1.31 µm with a 1 dB bandwidth of 31 nm.
• The design enables simple, single-step patterning and portability to existing foundry processes.

Conclusions:

• The proposed surface grating coupler offers a novel approach for high-efficiency fiber-chip interfaces on Si3N4 platforms.
• This design addresses limitations of current grating couplers, enhancing performance for Si3N4 integration.
• The technology is suitable for diverse applications, including datacom and quantum photonics.