Sub-decibel silicon grating couplers based on L-shaped waveguides and engineered subwavelength metamaterials Journal Articles uri icon

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  • The availability of low-loss optical interfaces to couple light between standard optical fibers and high-index-contrast silicon waveguides is essential for the development of chip-integrated nanophotonics. Input and output couplers based on diffraction gratings are attractive coupling solutions. Advanced grating coupler designs, with Bragg or metal mirror underneath, low- and high-index overlays, and multi-level or multi-layer layouts, have proven less useful due to customized or complex fabrication, however. In this work, we propose a rather simpler in design of efficient off-chip fiber couplers that provide a simulated efficiency up to 95% (-0.25 dB) at a wavelength of 1.55 µm. These grating couplers are formed with an L-shaped waveguide profile and synthesized subwavelength grating metamaterials. This concept jointly provides sufficient degrees of freedom to simultaneously control the grating directionality and out-radiated field profile of the grating mode. The proposed chip-to-fiber couplers promote robust sub-decibel coupling of light, yet contain device dimensions (> 120 nm) compatible with standard lithographic technologies presently available in silicon nanophotonic foundries. Fabrication imperfections are also investigated. Dimensional offsets of ± 15 nm in shallow-etch depth and ± 10 nm in linewidth's and mask misalignments are tolerated for a 1-dB loss penalty. The proposed concept is meant to be universal, which is an essential prerequisite for developing reliable and low-cost optical couplers. We foresee that the work on L-shaped grating couplers with sub-decibel coupling efficiencies could also be a valuable direction for silicon chip interfacing in integrated nanophotonics.


  • Benedikovic, Daniel
  • Alonso-Ramos, Carlos
  • Guerber, Sylvain
  • Le Roux, Xavier
  • Cheben, Pavel
  • Dupré, Cécilia
  • Szelag, Bertrand
  • Fowler, Daivid
  • Cassan, Éric
  • Marris-Morini, Delphine
  • Baudot, Charles
  • Boeuf, Frédéric
  • Vivien, Laurent

publication date

  • September 2, 2019