US Patent 7151635 Planar waveguide reflective diffraction grating

The invention relates to a planar waveguide reflective diffraction grating for use in an optical device, such as a wavelength division multiplexer, providing an increased bandwidth over conventional planar waveguide reflection diffraction gratings while eliminating the polarization dependent loss (PDL) typically associated therewith. Accordingly, a low order (<3), high aspect ratio (>10) grating is provided with a very short side wall (less than the wavelength of the optical signal) for use with incident angles of less than 15°.