Strip-Loaded Film Waveguide

Strip-Loaded Film Waveguide By V. RAMASWAMY (Manuscript received October 3, 1973) Low-loss strip-loaded guides, consisting of 7059 glass film on fused quartz substrate with sputtered Si02 as the loading strip, have been investigated. The number of modes supported by the strip-loaded structures were determined experimentally and compared with the values predicted by the application of an equivalent index analysis. Agreement between theory and experiment is good in the case of the smaller number of modes which result fro?n small loading, with the 7059 film thickness far away from cutoff. Current interest in optical fibers and thin film devices for use in optical communication systems has prompted the development of several new guided wave structures. One of these is a single material (SM) fiber1 representing an unclad fiber with a structural support. Basically, this is a planar slab waveguide structure with an increase in slab thickness in the central region where the guided light is concentrated. The region with the increased thickness can be considered a strip which loads a planar slab waveguide. 2 Another type of a strip-loaded structure is shown in Fig. 1 (a) where the planar waveguide has the higher index material and a strip of slightly lower index material acts as the loading. Since, within the region of the strip, most of the energy is confined in the film, requirements on the edge roughness of the strip are no longer as severe as in rectangular film waveguides 3 and therefore strip-loaded structures seem easier to fabricate.