Abstract

We propose a novel high-efficiency, low-reflection, and fabrication-tolerant perfectly vertical grating coupler (PVGC) with a minimum feature size $>200\mathrm{nm}$ to allow for fabrication using 193 nm deep-ultraviolet lithography. The structural parameters of PVGC were optimized by a genetic optimization algorithm. Simulations predicted the coupling efficiency to be $-2.0\mathrm{dB}$ (63.0%) and the back reflections to be less than $-20\mathrm{dB}$ in the wavelength range of 1532–1576 nm. The design was fabricated in a multi-project wafer run for silicon photonics, and a coupling efficiency of $-2.7\mathrm{dB}$ (53.7%) with a 1 dB bandwidth of 33 nm is experimentally demonstrated. The measured back reflection is less than $-16\mathrm{dB}$ over the C-band. The PVGC occupies a compact footprint of $30\mathrm{\mu m}\times 24\mathrm{\mu m}$ and can be interfaced with the multi-core fibers for future space-division-multiplexing networks.

© 2018 Optical Society of America

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