Efficient coupling between integrated optical waveguides and optical fibers is essential to the success of silicon photonics. While many solutions exist, perfectly vertical grating couplers that 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 efficiencies, however, has proven difficult. In this paper, we use inverse electromagnetic 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 99.2% (-0.035 dB) at 1550 nm. Using this base design as a starting point, we run subsequent constrained optimizations to realize vertical couplers with coupling efficiencies over 96% and back reflections of less than -40 dB which can be fabricated using 65 nm-resolution lithography. These results demonstrate a new path forward for designing fabrication-tolerant ultra high efficiency grating couplers.
[1]
Shankar Kumar Selvaraja,et al.
High efficiency DBR assisted grating chirp generators for silicon nitride fiber-chip coupling
,
2019,
Scientific Reports.
[2]
Yong Yao,et al.
Arbitrarily routed mode-division multiplexed photonic circuits for dense integration
,
2018,
Nature Communications.
[3]
V. Aksyuk,et al.
Photonic waveguide to free-space Gaussian beam extreme mode converter
,
2018,
Light: Science & Applications.
[4]
Siegfried Janz,et al.
Mapping the global design space of nanophotonic components using machine learning pattern recognition
,
2018,
Nature Communications.