Cube add/drop optical filter with low polarisation sensitivity using a metal island multilayer filter

An add/drop cube optical filter consisting of a metal island multilayer filter (IMF) sandwiched between two 45° glass prisms is proposed for wavelength division multiplexing applications. The light in a purposive wavelength region is reflected in a direction perpendicular to the incident light beam while other wavelengths are transmitted in a parallel direction. Filtering wavelengths, bandwidths, and device thicknesses can be controlled by the choice of structural parameters for the metal island films and the thickness of the glass layers. An IMF cube filter for 800 nm is designed. It is theoretically shown that the IMF cube filter is insensitive to polarisation in comparison with a conventional dielectric multilayer filter