Propagation and Excitation of Multiple Surface Waves

Open Access
Author:
Faryad, Muhammad
Graduate Program:
Engineering Science and Mechanics
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 19, 2012
Committee Members:
  • Akhlesh Lakhtakia, Dissertation Advisor
  • Akhlesh Lakhtakia, Committee Chair
  • Michael T Lanagan, Committee Member
  • Osama O Awadelkarim, Committee Member
  • Jainendra Jain, Special Member
Keywords:
  • surface plasmon-polariton waves
  • Kretschmann
  • grating
  • solar cell
  • sculptured thin film
  • rugate filter
Abstract:
Surface waves are the solutions of the frequency-domain Maxwell equations at the planar interface of two dissimilar materials. The time-averaged Poynting vector of a surface wave (i) has a significant component parallel to the interface and (ii) decays at sufficiently large distances normal to the interface. If one of the partnering materials is a metal and the other a dielectric, the surface waves are called surface plasmon-polariton (SPP) waves. If both partnering materials are dielectric, with at least one being periodically nonhomogeneous normal to the interface, the surface waves are called Tamm waves; and if that dielectric material is also anisotropic, the surface waves are called Dyakonov--Tamm waves. SPP waves also decays along the direction of propagation, whereas Tamm and Dyakonov--Tamm waves propagate with negligible losses. The propagation and excitation of multiple SPP waves guided by the interface of a metal with a periodically nonhomogeneous sculptured nematic thin film (SNTF), and the interface of a metal with a rugate filter were theoretically investigated. The SNTF is an anisotropic material with a permittivity dyadic that is periodically nonhomogeneous in the thickness direction. A rugate filter is also a periodically nonhomogeneous dielectric material; however, it is an isotropic material. Multiple SPP waves of the same frequency but with different polarization states, phase speeds, attenuation rates, and spatial field profiles were found to be guided by a metal/SNTF interface, a metal/rugate-filter interface, and a metal slab in the SNTF. Multiple Dyakonov--Tamm waves of the same frequency but different polarization states, phase speeds, and spatial field profiles were found to be guided by a structural defect in an SNTF, and by a dielectric slab in an SNTF. The characteristics of multiple SPP and Dyakonov--Tamm waves were established by the investigations on canonical boundary-value problems. The Turbadar-Kretschmann-Raether (TKR) and the grating-coupled configurations were used to study the excitation of multiple SPP waves. In the TKR configuration, which is easy to implement in a laboratory, a plane wave of either of the two linear polarization states was made incident on the metal-capped rugate filter of finite thickness and the absorptances were calculated using a numerically stable algorithm. In the grating-coupled configuration, which is required for solar cell applications, a plane wave of either polarization state was made incident on a rugate filter or an SNTF backed by a finitely thick metallic surface-relief grating and the total absorptance of the structure was calculated using the rigorous coupled-wave approach. In both the configurations, the excitation of SPP waves was inferred by the presence of those peaks in the absorptance curves that were independent of the thickness of the dielectric material. It was found that (i) it is the periodic nonhomogeneity (not the anisotropy) of a partnering dielectric material normal to the interface that is responsible for the multiplicity of surface waves; (ii) multiple SPP, Tamm, Dyakonov--Tamm, and Fano waves of the same frequency and different phase speeds and spatial profiles can be guided by an interface of two different materials provided that at least one of them is periodically nonhomogeneous normal to the interface; (iii) the morphology of the partnering dielectric material affects the number, the phase speeds, the spatial profiles, and the degrees of localization of the surface waves; (iv) the number of surface waves can be increased further by the coupling of two interfaces separated by a sufficiently thin layer; and (v) multiple surface waves can be excited in the TKR and the grating-coupled configurations both with the isotropic and anisotropic but periodically nonhomogeneous dielectric materials.