We report a simple numerical analysis to model the performance of in-line fiber optic components which rely on selective coupling between a polished single-mode fiber half-block and a highly multimode overlay waveguide. Important device performance characteristics of these devices are describable in terms of throughput power as a function of various waveguide parameters. Our model is based on treating the fiber as an equivalent planar waveguide (EPG) and obtaining the normal modes of the resultant multilayer structure through a matrix formalism. Throughput power exiting the fiber is obtained by calculating the overlap between the EPG mode and the normal modes. The agreement between our model and the reported experimental results on inline fiber modulators is shown to be excellent. This model should, therefore, be very useful in estimating the performance of a host of such in-line fiber components.

A normal mode analysis is applied to the investigation of the role of the superstrate in terms of its refractive index and thickness in estimating the performance of fiber refractometers and the tunability of fiber components based on evanescent coupling of a side-polished fiber to a multimode overlay waveguide. The model is shown to yield a complete transfer function and information about all the major characteristics of such in-line fiber devices. The results closely match the trends of the reported experiments.

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