A single-mode polymer-based graded index channel waveguide array with 1250 channels/cm packaging density on a cross-link induced photopolymeric thin lilm is reported. This array works at 1.31 and 0.63 ,um. Curved waveguides with radii of curvature from 1 to 40 mm were demonstrated. Waveguide propagation -loss in experimentally confirmed at 1.3 1 pm. Replacement of electrical interconnects requires an optical medium through which optical signals in either digital or analog format can be routed

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... om transmitters to receivers. If guided wave rather than free space routing is chosen for this purpose, two available choices are optical fibers and thin film waveguides. For machine-to-machine optical interconnects, optical fibers are the medium of choice. For interconnection scenarios such as backplane, intermodule, and intramodule, thin lilm waveguides are the major tools under intensive investigation."2 A thin film channel waveguide is the only guided wave interconnection device that is lithographically mass producible. This is especially important for applications requiring high density highly parallel interconnections, as do tine grained computing systems. In this letter, we report the first cross-link induced linear and curved channel waveguide and waveguide array on graded index (GRIN) photolime gelatin.3 The GRIN characteristic of the polymer thin film allows us to implement such a channel waveguide on any substrate of interest. After the polymer film was spin coated on a substrate, it was dipped into ammonia dichromate solution for sensitization. Formation of a channel waveguide was realized by cross linking the polymer film through ultraviolet exposure. It was observed that the cross-linked area has a higher index of refraction than the unexposed area. The index modulation due to the photoinduced cross link can be as high as 0.2.4 Consequently, the channel waveguide confinement and thus the packaging density (number of channels/cm) can be extremely high. Implementation of the waveguide pattern was realized either by laser beam direct writing or through a conventional lithographic process. The graph in Fig. 1 was produced by computer simulation based on the effective index method.5 It shows the optimal single-mode channel waveguide dimensions for an optical wavelength of 1.31 pm. The cutoff dimension is shown with index modulation as a parameter. Note that the cutoff boundary defined here is for Ef2, above which the channel waveguide becomes multimode. Marcatili's five-region method6 was also used for this purpose. The result (not shown) is very close to that of Fig. 1 . However, the cutoff dimension for Ei1',6 determined by the effective akurrently with