Compact efficient broadband grating coupler for silicon-on-insulator waveguides

We have designed a high-efficiency broadband grating coupler for coupling between silicon-on-insulator (SOI) waveguides and optical fibers. The grating is only $13 \mathit{\mu }\mathrm{m}$ long and $12 \mathit{\mu }\mathrm{m}$ wide, and the size of the grooves is optimized numerically. For TE polarization the coupling loss to single-mode fiber is below 1 dB over a 35-nm wavelength range when using SOI with a two-pair bottom reflector. The tolerances to fabrication errors are also calculated.