Studies Of Surface Plasmon Polaritons And Optical Nanoantenna

Surface plasmon polaritons (SPPs) are electromagnetic excitations that propagate like waves along the planar interface between a metal and a dielectric. Recently, an idea of engineering surface plasmon at low frequencies was proposed. That is, by cutting holes or grooves in metal surfaces to increase the penetration of EM fields into the metal, the frequency of existing surface plasmon can be tailored at will. The existence of such geometry-controlled SPPs, named spoof SPPs, has recently been verified experimentally in the microwave and terahertz regime. Recent researches indicated that different types of periodical metallic surface structures can be designed to support spoof SPPs. In this paper we study several types of spoof surface plasmon polariton waveguides and microcavity as well as optical nanoantennas. We find that spoof SPPs are supported in such surface structures such as a single row of metallic wedges periodically protruding out of a planar metallic surface, metallic V grooves whose walls are properly structured. Their dispersion properties and absorption losses are all controlled by the geometry of the surface structure. It is shown that such structures can sustain a mode of spoof SPPs in the terahertz region, whose fields are highly confined in the transverse plane. The guiding mode in these structures possess excellent properties such as good modal shape, large propagation length, and low bending loss, making them promising candidates for routing terahertz radiation in highly integrated circuits. We also design a coaxial terahertz plasmonic microcavity with ultra-small mode volume and high quality factor. Moreover, we design and study two new types of optical nanoantennas which can be used to localize and enhance magnetic field in high orders and focus light into a single deep subwavelength focal point at its resonance frequency.