L-shaped grating couplers engineered with subwavelength metamaterial for sub-decibel coupling loss

International audiencePractically attractive nanophotonic technologies, mostly realized on mature silicon-on-insulator (SOI) substrates, call upon availability of efficient input/output grating-coupled optical interfaces. In this work, we demonstrate, both theoretically and experimentally, ultra-directional L-shaped grating couplers for low-loss light coupling between standard optical fibres and SOI chips. Experimentally, we show grating couplers without and with subwavelength (SWG) transition, seamlessly fabricated with a 193-nm deep-ultraviolet lithography. Coupling loss of-2.7 dB is measured with a low return loss as low as-20 dB. In addition, we propose an apodized L-shaped grating coupler layouts with coupling loss below 1 dB. Apodized fiber-chip grating couplers are designed with a sub-decibel coupling performance, together with substantially relaxed requirements in terms of minimum feature dimensions