High-efficiency, low-back-reflection, S+C+L band grating couplers compatible with silicon photonics MPW platforms

Grating couplers enable vertical coupling between optical fibers and photonic chips without the need for specialized end-face processes; however, they suffer from bandwidth limitations. By fully utilizing the shallow etching processes available in silicon photonics multi-project wafer (MPW) platforms, two compact focusing grating couplers with minimum feature sizes of 100 and 200 nm are realized based on an efficient semi-inverse design method. The theoretical coupling efficiencies of two devices reach peak values of -2.1 and -2.5 dB, and are >-12.4 and -13.3 dB across the S-C-L bands, respectively. Within the C-band, the ±20 nm waveguide width deviations result in coupling efficiency offsets within 1 dB. The devices fabricated via the 180-nm DUV MPW process demonstrated a coupling efficiency better than -10 dB across a bandwidth of 115.5 nm. These grating couplers exhibit a comprehensive advantage over their counterparts in terms of high MPW-compatibility, large bandwidths, large fabrication tolerances, and low back reflections. They hold significant potential for wafer-scale in-line testing of silicon photonic chips for emerging applications such as S+C+L band optical communications.