Perfectly vertical surface grating couplers using subwavelength engineering for increased feature sizes.

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Nanotechnology

Background:

• Silicon-on-insulator (SOI) platform is crucial for integrated photonics.
• Vertical grating couplers are essential for efficient light out-of-plane coupling.
• Achieving broadband operation and low back-reflection simultaneously is a key challenge.

Purpose of the Study:

• To design and demonstrate vertical grating couplers with enhanced performance on the 220 nm SOI platform.
• To incorporate subwavelength metamaterials to improve feature sizes and optical characteristics.
• To achieve broadband low back-reflection and high coupling efficiency.

Main Methods:

• Utilized 3D-finite-difference time-domain (FDTD) simulations.
• Explored subwavelength metamaterials to optimize grating coupler design.
• Investigated a wide design space to identify optimal device parameters.

Main Results:

• Demonstrated vertical grating couplers with broadband low back-reflection (< -20 dB) over >100 nm bandwidth (C-band).
• Achieved high coupling efficiencies of 72% (106 nm minimum feature size) and 67% (130 nm minimum feature size).
• Maintained minimum feature sizes larger than 100 nm, enhancing fabrication tolerance.

Conclusions:

• Subwavelength metamaterials enable the design of high-performance vertical grating couplers on the 220 nm SOI platform.
• The proposed devices offer a favorable trade-off between coupling efficiency, back-reflection, and feature size.
• These findings contribute to more robust and manufacturable silicon photonic devices.