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Authors: M. Yang, Y. Yan, Z. Wu, G. Morthier, M. Zhao
Title: High performance grating couplers on 220nm thick silicon by inverse design for perfectly vertical coupling
Format: International Journal
Publication date: 7/2023
Journal/Conference/Book: Scientific Reports
Editor/Publisher: Nature, 
Volume(Issue): 13 p.18112
DOI: 10.1038/s41598-023-45168-2
Citations: 3 ( - last update: 14/7/2024)
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Efficient grating couplers (GCs) for perfectly vertical coupling are difficult to realize due to the second-order back reflection. In this study, apodized GCs (AGCs) are presented for achieving perfectly-vertical coupling to 220 nm thick silicon-on-insulator (SOI) waveguides in the C-band. We compare the performance of the AGCs to that of uniform GCs (UGCs) and demonstrate the superiority of the former. The AGCs were obtained through inverse design using gradient-based optimization and were found to effectively suppress back reflection and exhibit better matching to the Gaussian beam profile. The design and measurement results show that AGCs have a 3 dB lower coupling loss than UGCs. We fabricated focusing AGCs by electron beam lithography with a single, 70 nm shallow etch and a minimum feature size of 100 nm, which makes them compatible with CMOS technology. The AGCs achieved a coupling efficiency of −5.86 dB for perfectly vertical coupling. Overall, our results demonstrate the potential of AGCs for achieving high-performance coupling in the C-band on the SOI platform.

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