SUMMARY: The swollen-gel copolymerization of methyl methacrylate (MMA) with benzyl methacrylate (BzMA) was carried out in a poly(methyl methacrylate) tube in the presence of dicumyl peroxide (DCPO). The diffusion of the higher-refractive-index monomer BzMA into the swollen gel leads to the formation of a refractive index gradient (GRIN). After complete polymerization, a symmetric and bubble-free GRIN optical rod was obtained. It was found that high initiator concentrations cause a great shrinkage during polymerization and lead to the formation of bubbles. A long swelling process (t A 24 h) will cause the deformation of the cylindrical shape of the PMMA tube. The influence of initiator concentration, swelling temperature, swelling time, and polymerization temperature on the optical characteristics of the GRIN rods was investigated. An image with no distortion is observed through the GRIN rods prepared in this investigation. Resolution of 50 lm parallel lines transmitted through the GRIN rod was also examined.

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A modified finite element method with new solving algorithm is proposed to analyze electromagnetic problems of finite periodic structures. Dielectric-loaded parallel-plate waveguides with rectangular and triangular dielectric gratings are tackled as an example of the present approach. Numerical results are checked by the self-convergence test and by comparing with those obtained by other methods. Finally, the dependence of the scattering parameters on the frequency, the period number, and the grating height is analyzed and compared.