Waveguide echelle grating with low polarization-dependent loss using single-side metal-coated grooves

A novel type of echelle groove, in which only the illuminated facet is coated with metal, is proposed for the design of a planar waveguide echelle grating. Numerical simulations using the rigorous coupled-wave analysis show that the metal coating on the shaded facet of a conventional metallic echelle grating is the main source of the polarization-dependent loss (PDL) while it does not contribute to the improvement of the diffraction efficiency. It is also shown that the diffraction efficiency, especially for the transverse-magnetic mode, is enhanced and the PDL is greatly reduced when the proposed single-side metallic coating is used.