We analyze a compact double-grating coupler that provides coupling through radiation modes between two vertically stacked silicon-on-insulator waveguides. The grating is sufficiently strong to be considered a one-dimensional photonic bandgap structure that facilitates a short coupling length. Simulations suggest that a 29% coupling efficiency is achievable in coupling light from one waveguide to another with 12.9 µm long binary gratings. We found that the coupling efficiency is enhanced by Fabry-Perot resonance between two gratings. The coupling efficiency can be increased by use of a blazed grating. We use the eigenmode expansion method to design and optimize the binary grating coupler, and the results are verified by use of the finite-difference time-domain method.
© 2005 Optical Society of America
Po Dong and Andrew G. Kirk, "Compact double-grating coupler between vertically stacked silicon-on-insulator waveguides," Appl. Opt. 44, 7540-7547 (2005)