We present a technique for characterising metal-clad optical waveguides. Unperturbed Waveguides have been analysed and
the results compare well with the theoretical results from finite difference approximation of the scalar wave equation. Waveguides containing periodic perturbations have also been analysed. These perturbed waveguide structures have been characterised using a prism coupler and it has been found that there are images of the guided modes which line up well with theoretical predictions. These images are due to diffractions from the periodic perturbations within the waveguide structure.