Cladding-modulated Bragg gratings in silicon waveguides

A cladding-modulated Bragg grating implemented using periodic placements of cylinders along a waveguide is proposed in a silicon-on-insulator platform. The coupling strength is varied by changing the distance between the cylinders and the waveguide. This implementation enables precise control and a wide dynamic range of coupling strengths and bandwidths that can be practically achieved for applications with specific bandwidth requirements. Modeling results are verified experimentally, and we demonstrate coupling strengths differing by 1 order of magnitude (43 and 921 per cm) with bandwidths of 8 and 16 nm, respectively. This method scheme enables weakly coupled devices with high fabrication tolerance to be realized.