# Inverse Design of Near Unity Efficiency Perfectly Vertical Grating Couplers

## TL;DR

This paper employs electromagnetic inverse design to create high-efficiency, perfectly vertical silicon grating couplers with over 99% efficiency, simplifying optical fiber integration in photonics.

## Contribution

It introduces a novel inverse design approach to optimize perfectly vertical grating couplers with over 96% efficiency using a 65 nm process.

## Key findings

- Achieved over 99% chip-to-fiber coupling efficiency at 1550 nm.
- Designed fabricable vertical couplers with over 96% efficiency.
- Demonstrated the effectiveness of inverse design in photonic device optimization.

## Abstract

Efficient coupling between integrated optical waveguides and optical fibers is essential to the success of integrated photonics. While many solutions exist, perfectly vertical grating couplers which scatter light out of a waveguide in the direction normal to the waveguide's top surface are an ideal candidate due to their potential to reduce packaging complexity. Designing such couplers with high efficiency, however, has proven difficult. In this paper, we use electromagnetic inverse design techniques to optimize a high efficiency two-layer perfectly vertical silicon grating coupler. Our base design achieves a chip-to-fiber coupling efficiency of over 99% (-0.04 dB) at 1550 nm. Using this base design, we apply subsequent constrained optimizations to achieve vertical couplers with over 96% efficiency which are fabricable using a 65 nm process.