Katsu Rokushima

Analysis of dielectric lamellar gratings coated with anisotropic layers

The properties of a dielectric grating coated with an anisotropic layer are studied by using our previous analyses [ J. Opt. Soc. Am.71, 811– 818 ( 1981); IEEE Trans. Microwave Theory Tech.MTT-35, 937– 945 ( 1987)] for anisotropic dielectric gratings. Two peculiar properties that are due to the anisotropy of the material are shown. One is the enhancement of the change in polarization of the incident wave by the Bragg conditions for anisotropic gratings, which occurs in relatively deep gratings. The other is the anisotropic grating anomaly that is due to the excitation of the surface waves, which occurs in shallow gratings.

Analysis of diffraction in periodic liquid crystals: the optics of the chiral smectic C phase

A method for analyzing diffraction properties of periodic liquid crystals is presented that uses the previous theory for anisotropic dielectric gratings [ J. Opt. Soc. Am.73, 901 ( 1983)]. The method applies to any type of periodic liquid-crystal structure with arbitrary orientation of the helical axes. As an example of the present analysis, both forward and backward diffraction properties of a chiral smectic C phase are given for the incidence of linearly polarized and circularly polarized waves. An approximate two-wave analysis is also derived and is compared with the rigorous results.

Three-dimensional rigorous analysis of dielectric grating waveguides for general cases of oblique propagation

A rigorous analysis of wave guidance by dielectric grating waveguides is presented for the general case that both the grating vector and the direction of the guided wave have an arbitrary orientation in three dimensions. Guided modes then become TE-like and TM-like modes owing to the coupling between TE and TM waves. The analysis is formulated in a unified matrix form so that guidance properties can be obtained accurately in any level by systematic matrix calculations. The calculated results indicate that peculiar stop bands and leaky waves appear as a result of coupling between TE and TM waves.

Analysis of wave diffraction in a periodically bent nematic liquid crystal

Diffraction properties of a periodically bent nematic liquid crystal (PBNLC) are analyzed by using the previous theory for periodic liquid crystals [ J. Opt. Soc. Am. A4, 27 ( 1987)]. Wave propagation in the PBNLC is described by coupled-wave equations in a matrix form, and the diffraction and dispersion properties of the PBNLC are given. Approximate two-wave analysis taking into account the boundary effect is also derived, and good agreements between the approximate and rigorous solutions are shown.

Numerical Analysis Of Multistep Dielectric Gratings

An exact numerical method of analyzing deep dielectric gratings with multistep lamellar profiles is presented. This method is able to predict the diffraction efficiencies of dielectric gratings for both TE and TM polarizations. In this paper we use a modal expansion method in terms of modal functions which are rigorous solutions of the Maxwells equations and fulfill the boundary conditions on the upright enclosing sides of the rectangular profiles. The coefficients of the modal expansion are determined such that the mean-square boundary residual becomes minimum, and the sequence of approximate solutions converges rapidly and monotonically with respect to the truncation size of the expansion order with help of the smoothing procedure of the modal fields. To show the validity of this algorithm in the sinusoidal surface-relief gratings, the results are compared with those obtained by other methods.

Modal Expansion Method For Dielectric Gratings With Rectangular Grooves

An exact method of analyzing the dielectric gratings with rectangular grooves is presented. The most common of rigorous approaches are the expansion-methods such as coupled-wave approaches and modal approaches, which expand the fields in terms of space harmonics based on the Floquets theorem. However, these methods are not rigorous in the strict sence for the numerical analysis of dielectric gratings with rectangular grooves, since in the case of rectangular shapes the Fourier series sometimes fails to converge with the increase of the number of order in the expansion. In this paper, a rigorous numerical method for rectangular-groove gratings is presented by using modal expansion in terms of modal functions consisting of the Bloch waves inside the periodic stratified media. The convergence of the solutions in this method is very rapid with the increase of the truncation size retained in the calculation, moreover the accuracy of the solutions can be checked by the energy-conservation and the square-errors of the electromagnetic fields on the boundaries. The scattering problems for both E-mode and H-mode polarizations are treated.

Scattering And Waveguiding Properties Of General Slanted Gratings Consisting Of Anisotrodic Media

A method for analyzing slanted anisotropic gratings is presented. The method allows treatment of scattering and guiding of waves by a general dielectric grating with fringes of any orientation in three dimensions. Generalized coupled-wave equations are derived in a unified matrix form expressing the coupling of the space harmonics in the grating region. By introducing the concepts of the transmission and boundary matrices, the solutions are obtained rigorously by systematic matrix calculations that are easily implemented on a computer. The diffraction efficiencies of anisotropic gratinas and the properties of dielectric waveguides with slanted gratings are shown as numerical examples.

Propagation characteristics of anisotropic chirowaveguides

A rigorous analysis of anisotropic chirowaveguides is presented for the case of oblique propagation. The analysis is formulated in a unified matrix form, so that propagation characteristics can be obtained by systematic matrix calculations. The numerical results clarify that not only surface waves but also leaky waves exist owing to the anisotropy and chirality of the medium.

Wave Diffraction And Guidance By Anisotropic Dielectric Waveguides With Space-Time Periodic Index Modulation

A rigorous analysis for the wave diffraction and guidance in a planar anisotropic medium with tensor permittivity which is modulated periodically with respect to space and time is presented. The method applies to any anisotropic medium, any polarization of the incident plane wave and any orientation of the grating vector. The analysis is formulated in a unified matrix form so that calculations can be performed systematically. Numerical examples of both scattering and guiding properties peculiar to anisotropic waveguides are shown.

Nonlinear effects in multifrequency acousto-optic diffraction

A perturbation formulation is developed for the analysis of acoustooptic diffraction with multiple acoustic waves at different frequencies. The rigorous modal theory and perturbation method are used for the quantitative evaluation of nonlinear effects occurring in acoustooptic spectrum analysis and optical information processing. Various multifrequency diffraction effects were investigated by using rigorous modal approach and approximate perturbation approach. Sample calculations are presented for various regimes of diffraction. A comparison of perturbation approach, coupled wave approach, and rigorous modal approach is made.