Optical multiplexing using transparency window of good conductors

Thin metal films are excellent reflectors and extremely opaque at microwave and mm-wave frequencies. Bulk metal, however, becomes partly transparent at optical frequencies due to the shape of the Lorentz-Drude permittivity function at that frequency regime. We explore this property for designing optical filters composed of a finite number of periodically placed thin metal films, supported by conventional dielectrics. The resulting filters exhibit comb-filter multiplexing characteristics similar to Bragg reflectors at frequencies higher than 10/sup 14/ Hz, but, unlike Bragg reflectors, are completely opaque to any smaller frequencies.