Sub-decibel off-chip fiber couplers based on L-shaped waveguides and subwavelength grating metamaterials

Uniform grating couplers based on versatile L-shaped waveguides are experimentally demonstrated, with coupling loss of -2.7 dB and back-reflections of -20 dB. Apodized couplers with subwavelength-grating metamaterials predict improved fiber-chip coupling down to -0.46 dB within device layouts compatible with lithographic technologies available in nanophotonic foundries.