Exceptional Electromagnetic Surface Waves and Compound Waves

Open Access
- Author:
- Zhou, Chenzhang
- Area of Honors:
- Engineering Science
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Akhlesh Lakhtakia, Thesis Supervisor
Lucas Jay Passmore, Thesis Honors Advisor
Tom Mackay, Thesis Supervisor - Keywords:
- Exceptional guided waves
Electromagnetism
Optics
Surface waves
Compound waves
Maxwell equations - Abstract:
- The propagation of electromagnetic surface waves is guided by the interface of two dissimilar mediums. The electromagnetic fields have significant magnitudes only in the vicinity of that interface. Researchers have identified various types of electromagnetic surface waves such as Uller--Zenneck waves, Dyakonov surface waves, Tamm waves, Dyakonov--Tamm waves, and surface--plasmon--polariton waves. Due to their sensitivity to the constitutive parameters of the partnering mediums, they have been exploited in many applications such as sensing and microscopy. In particular, the ability of propagation with negligible attenuation of the Dyakonov surface wave makes it promising in long-range communications. Apart from the propagation of surface waves, compound waves guided by tri-material structures also caught the attention of researchers. The propagation of compound waves arises due to the strong interaction between the two parallel interfaces, which is greatly dependent on the thickness of the thin film sandwiched in between two mediums. The thickness of the thin film is usually in the order of 10-50 nanometers, while the thicknesses of the other two mediums are assumed to be so much larger as to represent half-spaces. In particular, if the thin film is taken to be a metal, then one or several compound--plasmon--polariton wave modes may propagate. The propagation of multiple wave modes makes them promising in applications such as optical sensing, microscopy, and solar energy harvesting. In the past decades, research into electromagnetic surface waves and compound waves has been focused on the propagation of unexceptional surface waves and unexceptional compound waves. The surface and compound waves mentioned above fall into these two categories. The propagation of these waves is restricted to a continuous range of directions in each quadrant, usually with four-fold symmetry. The fields in the partnering mediums exhibit exponential decay from the interface(s). This thesis work introduces electromagnetic surface waves of a new type called exceptional surface waves. Under this category, various types of surface waves are investigated: Dyakonov--Voigt waves, Dyakonov--Tamm--Voigt waves, and surface--plasmon--polariton--Voigt waves. These surface waves require that at least one of the partnering mediums is anisotropic. Similarly, electromagnetic compound waves of a new type called exceptional compound waves are introduced. Of the two mediums with larger thicknesses, at least one has to be anisotropic for the propagation of exceptional compound waves. An exceptional compound--plasmon--polariton wave is an example under this category. Differently from their unexceptional counterparts, the propagation of exceptional surface waves and compound waves is allowed at discrete propagation angles in each quadrant, so far exclusively with four-fold symmetry. The emergence of those exceptional guided waves is due to the non-diagonalizable form of the propagation matrix associated with the anisotropic medium. As a result, they are fundamentally different from unexceptional guided waves in that their fields in the anisotropic medium decay as the product of a linear function and an exponential function of the distance away from the interface.