Surface Waves Guided by Anisotropic Dielectric Materials in the Grating-Coupled Configuration

Abstract

Surface waves are electromagnetic waves that are guided by an interface of two dissimilar materials. If one of the two partnering materials is a metal, the surface waves are called surface-plasmon-polariton (SPP) waves. If both partnering mate rials are dielectric with at least one being anisotropic, the surface waves are called Dyakonov surface waves. In this thesis, the excitation of both the SPP waves and Dyakonov surface waves was studied when the partnering dielectric material is either uniaxial or biaxial. The biaxial material used here is a columnar thin film (CTF). CTFs are porous and have a columnar morphology with columns lying in a plane called the morphologically significant plane. The excitation of surface waves guided by a CTF deposited on either a one-dimensional metallic surface-relief grat ing, or a one-dimensional isotropic dielectric surface-relief grating was studied, when the grating plane, the plane of incidence, and the morphologically signifi cant plane of the CTF are all different. The incident plane wave in this grating coupled configuration can be either p- or s-polarized. The absorptances were plot ted against the polar angle of incidence at a fixed value of the free-space wave length and absorptance peaks were correlated with the solution of the dispersion equation of the underlying canonical boundary-value problem for the identifica tion of surface waves. Both the p-polarized and s-polarized plane waves can excite surface waves, provided that either the plane of incidence and/or the morpholog ically significant plane of the CTF do not coincide with the grating plane. No, one, or multiple surface-wave excitations are possible, depending on the orientations of the grating plane and the morphologically significant plane with respect to the plane of incidence. The direction of propagation of surface wave thus excited may not wholly lie in the plane of incidence. The excitation of SPP waves guided by a CTF deposited on a one-dimensional metallic surface-relief grating was investigated for sensing the refractive index of a fluid infiltrating that CTF. The Bruggemann homogenization formalism was used to determine the relative permittivity scalars of the CTF infiltrated by the fluid. Change in the refractive index of the fluid was sensed by determining the change in the incidence angle for which an SPP wave is excited on illumination by a p polarized plane wave, when the plane of incidence is taken to coincide with the grating plane but not with the morphologically significant plane of the CTF. Multi ple excitations of the same SPP wave were found to be possible depending on the i ABSTRACT refractive index of the fluid, which could help increase the reliability of the results by sensing the same fluid with more than one excitations of the SPP wave. Also, the excitation of the high-phase-speed Dyakonov surface waves guided by a surface-relief grating of a uniaxial dielectric material and an isotropic dielectric ma terial was theoretically studied for illumination by p- and s-polarized plane waves. Both p- and s-polarized plane waves can excite the high-phase-speed Dyakonov surface waves. No, one, or multiple excitations of high-phase-speed Dyakonov surface waves are also possible, depending upon the choice of the partnering ma terials and the period of the surface-relief grating. Excitation of a high-phase-speed Dyakonov surface wave as a specular Floquet harmonic was also conjectured. The purpose of this research was to study the propagation and excitation of the sur face waves. It was found that (i) the excitation of surface waves is dependent on the orientation of the grating plane, morphologically significant plane of the CTF, and the plane of incidence; (ii) multiple surface waves can be excited for p-polarized and s-polarized incidence, depending on the orientation of different planes; (iii) for certain orientations of the grating plane, morphologically significant plane, and plane of incidence, no surface wave may be excited; (iv) no, one, or multiple ex citations of high-phase-speed Dyakonov surface wave are possible with the phase speed higher than the phase speed of light in the partnering bulk materials; (v) the excitation of high-phase-speed Dyakonov surface waves as a specular Floquet har monics is also possible; and (vi) multiple excitations of an SPP wave can be used for sensing the refractive index of a fluid infiltrating the CTF.