Modes of a 3-dimensional sandwich-ribbon optical waveguide

Sandwich-ribbon-fibre waveguides are intended for directional coupling to and from thin-film optical integrated circuits. The propagation characteristics of a 3-dimensional ribbon fibre have been studied using the synchronous angles of a prism coupler, and by observing the near- and far-field patterns of the excited modes. Although the cross-section of the guiding region is not rectangular, it has been found that the modal characteristics can be adequately described using approximate solutions developed for rectangular waveguides.