High-performance and compact binary blazed grating coupler based on an asymmetric subgrating structure and vertical coupling

A high-performance and compact fiber-to-waveguide binary blazed subwavelength grating coupler was designed based on silicon-on-insulator. By the appropriate choice of waveguide/grating parameters, including thicknesses, periods, height, and fill factor, to optimize the mode matching, a relatively high coupling efficiency was obtained for the fiber and waveguide interface. Moreover, perfectly vertical fiber coupling is achieved by using an asymmetric subgrating structure in which a period consists of two subgratings with identical etching height and different widths. Coupling efficiency as high as 69% at a wavelength of 1.52 μm and 65% at a wavelength of 1.55 μm is calculated. Simultaneously, the 1 dB wavelength bandwidth is around 80 nm. The coupling efficiency can reach up to 80% or so if Bragg reflector layers are added. Finally, the device layout is simple, feasible, one-step etched, and compatible with standard complementary metal-oxide semiconductor technology processing.