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 TE
0
mode is coupled out into the substrate, whereas the TM
0
mode is transmitted with very low losses. The best extinction ratio measured is 18 dB. The polarizer can be used as a TE
0
mode coupler into symmetrical waveguides as well.