Measurement on positive-permittivity metal-clad waveguides

A few metals exhibit a permittivity whose real part is positive at nm, in contrast to most metals which have a permittivity with a large, negative real part. The effects of two metals, chromium and germanium, have been measured when used as claddings on polystyrene asymmetrical waveguides. The measurements confirm recent theoretical predictions, and indicate attenuations greater than an order of magnitude over measured attenuations in silver, aluminum, and gold. Techniques used in making measurements of attenuations up to 100 dB/cm are described, and experimental values are compared with predicted attenuations. They are shown to agree with calculated values when additional mode-conversion losses are taken into account. The measured mode-index data also confirm the presence of guided modes which have a mode index less than that of the second cladding region (air). Such a propagating wave has been shown to exist in both of the metal claddings examined.