| Surface states are a kind of localized states found at the interfaces between two different media. One of the most known types of such waves is surface plasmon polaritons(SPPs), which are electromagnetic excitations that, being coupled to surface collective oscillations of free electrons in a metal, are bound to and propagate along dielectric-metal interfaces. SPPs are renowned for their ability to concentrate electromagnetic fields beyond the diffraction limit, while enhancing local field strengths by several orders of magnitude, becoming the most likely way to achieve all-optic integrated circuit. In addition, SPPs plays an significant role in data storage and solar cell, etc. The other types of commonly known surface waves are optical Tamm states(OTS), which are the electromagnetic equivalent of modes confined to surface states for electrons originally described by Tamm, were first named by A.V.Kaokin in 2005. Such lossless surface wave can be generated in the PC heterojunction or at the interface between a metal and a distributed Bragg reflector without polarization dependence, that represent an excellent alternative for a variety of optical elements with a functionality relying on the surface waves.The main work involved in this dissertation is about those two kinds of surface waves, and be presented as follow:Firstly, a plasmonic lens with long focal length and tight focusing under illumination with a radially polarized light has been present, in an optimized PL design, a focal spot with ～2.5λ0 DOF, ～0.388λ0 FWHM, ～3.22λ0 focal length is achieved under the illumination with a radially polarized light(λ0=632.8 nm).Plasmonic lens(PL) is a nano-optical device, with which a tight focusing spot in a subwavelength-scale can be achieved by exciting and controlling surface plasmon polaritons(SPPs), thus the diffraction limit can be broken.In this dissertation, under an illumination with a radially polarized light, a new type of plasmonic lens is proposed to achieve a long depth of focus(DOF), a long focal length and a sub-wavelength scale tight focusing spot. This kind of plasmonic lens consists of a T-shape micro-hole, concentric rings and multi-level step-like structures. The focusing properties of such plasmonic lenses are analyzed with the finite element method(FEM). Simulation results show that SPPs can be excited efficiently in such structures and the tight-focusing is realized via the multiple-beam interference between the light radiated from the concentric rings and the transmitted light from the center hole. The T-shape micro-hole and step-like concentric ring structures can provide a control on the phase modulation and the propagation direction of the SPPs propagating along the bottom of the groove; thus lead to a compressed focal spot, a longer focal length, an increased depth of focus, and improved focusing properties. The PL structure is compact, and can be easily integrated with other nano-devices. The proposed PL has potential applications in the nano-scale photonic integration, the near-field imaging and sensing, the nano-photolithography, and other related areas.Secondly, the OTS generated at the interface between a DBR and a metal has been investigated by means of transfer matrix method and finite element method. The study elucidate that with increment of the thickness of metal, OTS’s excitation wavelength will first move towards the short-wave section, then become a fixed value. The Bottom layer’s thickness will also influence the OTS’s excitation wavelength. By means of finite element method, a special DBR-metal structure which a trapezoidal groove has mounted on the metal layer has been investigated. The study elucidate that with a trapezoidal groove mounted on metal layer, the transmission of TM polarized light has been enhanced, and the enhancement is depend on the trapezoid’s flare angle. Those result can be a good reference to design nano-optical sensor, i.e. non-cavity polaritons laser and optic-biosensor. |
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