A riblike waveguide structure consisting of three isotropic transparent layers on an isotropic transparent substrate is shown to be capable of selectively guiding only the TE-like (TM-like) mode if the waveguide axis is defined by a trough (ridge) in the low-index middle layer. Guidance in the film plane arises from the joint dependence of the planar waveguide mode-propagation constants on the strength of evanescent coupling between high-index layers and on the difference between the propagation constant for the three-layer structure and that for a single, isolated layer on the same substrate. The mode with polarization opposite the guided one radiates away from the guide axis in the film plane. Because the insertion loss arises only from scattering and mode conversion at boundaries, it is expected that high extinction ratios, accompanied by tolerable insertion losses, will be realized.
© 1982 Optical Society of AmericaFull Article | PDF Article
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