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. The multiplexer/demultiplexer according to the present invention includes input and output ports optimally positioned in accordance with the grating facet diffraction envelope to minimized back reflection to the input ports and maximize output light collected from different diffraction orders.