Abstract
The paper deals with the problem of electromagnetic TE-polarized monochromatic light diffraction on three-dimensional thickening of the waveguide layer of regular three-layered open planar dielectric waveguide, which forms thin-film waveguide lens. The authors propose an approximate mathematical model in which open waveguide is placed inside the auxiliary closed waveguide, that leads to well-posed diffraction problem. It is shown, that properties of guided modes of the open waveguide are stable with respect to shifts of the closed waveguide boundaries. So, the proposed approach describes the propagation of polarized light in the open smoothly irregular waveguide adequately. The three-dimensional thickening of the waveguide layer forces us to deal with electromagnetic field in vector form due to depolarization effect. The diffraction problem, presented in the work, is solved in adiabatic approximation by the small parameter of irregularity of the waveguide layer. The numerical experiments show that decreasing of the small parameter tends the reflection coefficient matrix to zero-matrix, tends the transmittance coefficient matrix to identity matrix, and besides the non-diagonal matrix elements, corresponding to modes interaction, tend to zero by an order faster than diagonal matrix elements, which shows that depolarization effects in the given configuration can be neglected.
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