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Sol-gel derived silica, siica-titania, and tantala coatings were covered with a thin metal film andtranslated across a Nd:YAG laser beam (1.06 jim). The laser energy was absorbed by the metal film, whichheated the underlying sol-gel coating. This heating densified the sol-gel coatings, thereby increasing theindex ofrefraction of the laser heated region, and forming channel waveguide structures in all three sys-tems. The channels formed by this technique were etched, to remove the undensified regions, which resultedin ridged waveguide structures. The structures were also produced by depositing a metal pattern usingphotolithographic techniques, and rastering the laser across the entire sample. The refractive indicies oflaser densifled and furnace densified silica coatings were similar. Large differences were observed in theindicies oflaser and furnace densified coatings for the siica-titania and tantala systems. . 1. INTRODUCTION One of the basic components in integrated optical circuits is the channel waveguide. The channelwaveguide provides two-dimensional confinement ofthe optical signal, which permits the routing of signalsbetween various input, output, and processing components on a chip. While most often used as a passivecomponent, channel waveguides can also be fabricated in electro-optic and semiconducting materials such asLiNbO3 and GaAs, where they actively participate in signal processing. Various geometries (e.g., ridged andimbedded channel guides and strip-loaded planar guides) can be used to synthesize channel waveguides (Fora detailed discussion see Reference 1). However, the basis for all ofthese geometries is the formation of achannel which guides light when it is surrounded on all sides by lower index material.The modal properties of the channel waveguide are determined by the index difference between thewaveguide and its surroundings, and by the waveguide dimensions. When the index differences are small,on the order of 1 to 2%, the single mode operation requires channel dimensions on the order of one to severaloperating wavelengths. For index differences of 10 to 30% these dimensions are reduced to 1/4 to 1/3theoperating wavelength. When the channel dimensions exceed these minimum values, multi-mode operationis possible. For most applications minimum operating efficiencies require that channel waveguide losses beno larger than about 1 dB/cm. However, losses approaching 0.1 dB/cm are much more desirable.A wide range of techniques have been used to synthesize both active and passive channel waveguides.These include radio frequency sputtering,2 chemical vapor deposition,3'4 liquid phase epitaxy,5 vapor phase |
