R. K. Shevgaonkar

Bio: R. K. Shevgaonkar is an academic researcher. The author has contributed to research in topics: Multi-mode optical fiber & Dielectric. The author has an hindex of 1, co-authored 1 publications receiving 11 citations.

Multimode propagation in anisotropic optical waveguides

Abstract: Using far from cutoff approximation (2a/λ0 ≫ 1) we have derived elegant expressions for the characteristic equations and their relevant solutions to determine the guided wave features of an optical waveguide having an axial dielectric anisotropy. Also, the attenuation constant has been calculated following the concept of a complex permittivity in a lossy medium. For TE and TM, as well as hybrid modes studied here, the results computed by the approximate method show very good agreement with those of the exact analytical solutions. The dependence of the power carrying capacity and attenuation on the waveguide parameters highlights the usefulness of the dielectric anisotropy in optical waveguides.

The Inverse Problem for Biaxial Materials

Abstract: Theory and measurements for the determination of the constitutive parameters of an anisotropic material are described, when a slab of the material is inserted in a rectangular waveguide. If both epsilon and µ tensors have zero off-diagonal elements (biaxial material), then the six diagonal elements can be determined by measuring amplitude and phase of reflection and transmission coefficients. If the material is nondispersive, two sets of measurements at two different frequencies are sufficient, under TE/sub 10/ excitation. In the more general case of a lossy and dispersive material, two sets of measurements at the same frequency under TE/sub10/ and TE/sub20/ excitations are needed. An experimental setup for the latter case is described.

Analysis of cladded uniaxial single-crystal fibers

Abstract: A complete analysis for a uniaxial core–uniaxial cladding step-index fiber is presented. Numerical results of a few lowest-order modes are presented for weakly guiding LiNbO3 single-crystal cladded fibers. We find that the fundamental mode in a uniaxial fiber is not linearly polarized but has significant orthogonal components, even though the fiber is under weak guidance and has no modal birefringence because the wave propagation direction is the crystalline Z axis. We conclude that large anisotropy can cause the relatively large minor field in a uniaxial fiber, but modal birefringence is not necessarily involved. The electrical lines of the fundamental mode for a uniaxial fiber are also considerably different from those of an isotropic one, but eigenvalues and fractions of power in the core are similar.

Reflection and transmission for gyroelectromagnetic biaxial layered media

Abstract: A planar structure consisting of layers of different media is considered. The material of each layer is linear and homogeneous but anisotropic and, in general, exhibits biaxial, gyroelectric, and gyromagnetic properties. Thus most materials used in practice fall into the general category considered here. The structure has free space on one side and an isotropic medium (e.g., a dielectric or a metal) on the other side. A plane electromagnetic wave with arbitrary direction and polarization is incident upon the structure. The propagation constants and the components of the electric and magnetic fields are determined in each layer. A chain-matrix approach is implemented to obtain reflection and transmission coefficients for the structure.

Dyadic green's functions for a two-layer biaxially anisotropic medium

Abstract: The dyadic Green's functions (DGF's) of a two-layer biaxially anisotropic medium are derived The principal coordinate system of the anisotropic medium is allowed to have arbitrary orientation with respect to the layer geometry First, the unbounded DGF is derived using the Fourier transform method Hence the DGF's for the two-layer medium in the spectral domain are formulated Using a matrix method the coefficients of the two-layer DGF's are expressed in terms of half-space Fresnel reflection and transmission coefficients To complete this procedure the various relevant half-space Fresnel coefficients are derived The form in which the results are presented has a physically meaningful and compact structure A numerical example is provided where we have computed the reflectivities

Transversely anisotropic curved optical fibers: variational analysis of a nonstandard eigenproblem

Abstract: The variational principle for nonstandard eigenvalue problems, recently reported by one of the authors, is applied for the study of guided-wave propagation in an anisotropic dielectric waveguide. A stationary functional is derived for the general dielectric waveguide with transverse anisotropy. The functional is tested for the well-known case of an isotropic step-index single-mode fiber. It is seen that for simple trial functions with only two parameters, a good accuracy is obtained. For two types of transversely anisotropic step-index fibers, relations between the propagation factor, anisotropy parameter, dielectric parameter, and frequency are calculated. The functional does not assume weak guidance condition nor perturbational anisotropy and, hence, is also applicable for other dielectic waveguides. In this application, only a modest computer or a programmable calculator is needed. Moreover, the spurious modes causing confusion in the finite-element method of calculation do not appear with the present method.