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We suggest a three-dimensional theoretical model to explain the origin of light wave propagation in a quasiwaveguide structure formed by a thin film of refractive index smaller than the substrate. The physical principles involved are illustrated by the use of a combination of multiple-wave interference and coherent multiple scattering. Not only the theoretical details and the important analytic formulas describing the properties of wave propagation in the quasiwaveguide were given, but also the positions and linewidths of the quasiwaveguide modes, the intensity distribution in the film, the intensity of the reflected spot, and the intensity distribution of the scattered light (m lines) are studied in detail. We divide the modes in the quasiwaveguide into three kinds: cavity modes, leaky modes, and degenerate modes. Some interesting problems are discussed. We investigate the properties of wave propagation in a quasiwaveguide made with a doped polymer film and discuss the origin of scattering.

We present a simple and efficient technique for evaluating the optical losses of a planar film by use of a quasi-waveguide configuration and a prism film coupler configuration. The technique can separate two contributions to optical loss: that from the surface scattering caused by the roughness of surface and that from volume losses including volume scattering and volume absorption.

Several kinds of azo‐dye polymer films of the guest‐host system were prepared by the spin‐coating method. Four disperse red (DR) dyes of DR1, DR19, DR54 and DR73 were chosen as second order nonlinear optical active chromophores with polymer matrixes such as poly (methyl methacrylate) PMMA or polycarbonate (PC). The processing conditions such as heat‐treatment, substrate, and film storage condition on all‐optical poling characteristics of azopolymers have been investigated. It is found that the second harmonic generation intensity is very sensitive to the chromophores and processing parameters. Some explanations have been proposed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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