Ultra-broadband high-efficiency grating couplers for light injection in horizontal slot waveguide

An ultra-broadband high-efficiency grating coupler has been designed for the +1 diffraction order at an operating wavelength of 1.55μm for TM polarization in horizontal slot waveguide. The coupling bandwidth is significantly increased by properly raising the height of unperturbed silicon ridges, meanwhile the coupling efficiency is also enhanced. The 1dB bandwidth is 70nm which doubles the previously reported value; it is much larger than the slab waveguide grating couplers. Maximum coupling efficiency of 72% has been achieved for positive detuned grating couplers with incident light from SMF at 8°. The approaches for parameters optimization and maximum coupling efficiency are discussed based on the simulation results. Sensitivity to fabrication and alignment tolerances of the structure has also been analyzed.