Metal-clad waveguide as cutoff polarizer for integrated optics

Propagation constants, attenuation, and field distributions of optical modes in dielectric waveguides clad by a thin metal layer are calculated. It is shown that by reducing the metal thickness, the attenuation of optical modes reduces in such a way that short metal-clad devices become possible even in thin guides with thicknesses near cutoff. As an application, a cutoff polarizer in symmetrical waveguides has been built by depositing a small thin silver stripe on the surface of the guide. By this structure the TE0mode is coupled out into the substrate, whereas the TM0mode is transmitted with very low losses. The best extinction ratio measured is 18 dB. The polarizer can be used as a TE0mode coupler into symmetrical waveguides as well.