The efficiency of an N.times.N waveguide grating router may be increased in many applications by incorporating at least one output waveguide, such as an (N+1).sup.st waveguide, positioned for capturing second order diffraction optical energy from a free-space region in the router. The second order diffraction...http://www.google.es/patents/US5600742?utm_source=gb-gplus-sharePatente US5600742 - Wavelength grating router with output coupler
