An optical coupler comprises an input waveguide, an intermediate waveguide, an output waveguide, a first grating situated between the input and intermediate waveguides, and a second grating situated between the intermediate and output waveguides such that, in use, light propagating in the input waveguide...http://www.google.ca/patents/US7221825?utm_source=gb-gplus-sharePatent US7221825 - Optical coupler
