Study On The Directional Surface Plasmon Excitation And Nano-focus Devices Based On The Phase Control

The surface plasmon polariton is generated by the collective oscillation of the interacting light wave and the free electrons in the metal. It has three typical characteristics including the wavelength shorter than that of the illumination, the localized surface enhancement and the extraordinary dispersion relation, and most of researches on the surface plasmon are related to these three properties. The sub-wavelength property can break the diffraction limit of the traditional optical device (the focal spot size is larger than 1/2 wavelength) and hopefully can be applied to realize the highly integrated light and electricity of micro-nano size. Localized surface enhancement can strengthen the Raman scattering and then improve the sensitivity and resolution of the related detection devices. With the development of the nano-processing technology and the related computer processing capability, the subwavelength photonic device based on the metal surface plasmon has been extensively studied numerically and experimentally, every hopefully it can be applied in the nano-lithography, optical microscopy, biological imaging and optical data storage, etc. In this paper, starting from the Maxwell’s equations, we illustrate the basic characteristics of the surface plasma based on the interaction between light and metal, and then the directional excitation enhancement and nano-devices for the prolonged focal spot are realized by modulating the phase distribution of the surface plasma wave.With the model of non-periodic grating structure for nano-focus lens, the effective refraction index inside the nano-slits is calculated, and accordingly the width of nano-slits can be determined according to the required phase value of the exited light. Using the principle of phase matching similar to that widely adopted in the nonlinear optics, a new kind of structure for the directional surface plasmon excitation is designed. Furthermore, with the resonant transmission principle, a nano-antenna is added to each nano-slit and then the energy transmitting the slit increases remarkably. At last the by periodically fabricate this kind of nano-structure on the metal screen and make them to fill the constructive interference condition, the surface plasmon is further strengthened in the desired direction. With this meth the energy of the surface can be increased by about 10 times. This kind of device has the advantages of simple structure, compact system, which has an important meaning for micro nano optical transmission and high density optical integrated field etc. Secondly, on the basis of non-periodic focusing grating, a new optimized design is proposed to make focus long and small. It can realize the adjustment of the diffident depth of focus by changing the width of the slit, making the phase distribution satisfies different cone apex angel of lens. Instead the light of the topological charge for 1 of the optical vortex (To two-dimensional structure, the light on both sides of the center had a difference pi phase), the metallic lens can realize the long focal depth of hollow beams, t, long, the combination of the two can further improve the resolution. This structure has a certain reference value in the breakthrough of optical diffraction limit and sub long focal depth beam.