Inverse design of near unity efficiency perfectly vertical grating couplers

Area of Science:

• Photonics
• Materials Science
• Electrical Engineering

Background:

• Efficient coupling between optical fibers and integrated waveguides is crucial for silicon photonics.
• Perfectly vertical grating couplers offer reduced packaging complexity but achieving high efficiency is challenging.

Purpose of the Study:

• To optimize a high-efficiency, two-layer, perfectly vertical silicon grating coupler using inverse electromagnetic design.
• To achieve high coupling efficiency and low back reflection for fabrication-tolerant devices.

Main Methods:

• Utilized inverse electromagnetic design techniques.
• Optimized a two-layer silicon grating coupler structure.
• Performed constrained optimizations to meet specific performance targets.

Main Results:

• Achieved a base chip-to-fiber coupling efficiency of 99.2% (-0.035 dB) at 1550 nm.
• Realized vertical couplers with over 96% coupling efficiency and back reflections below -40 dB.
• Demonstrated designs are manufacturable with 65 nm-resolution lithography.

Conclusions:

• Developed a novel approach for designing ultra-high efficiency, fabrication-tolerant grating couplers.
• The optimized design significantly advances the potential for simplified packaging in silicon photonic integrated circuits.
• This work paves the way for more efficient and robust silicon photonic devices.