Based On The Imaging Mechanism Of Surface Plasmon Of The Metal Focusing Lens And Optimization Design

Surface Plasmon Polaritons(SPPs), as the electromagnetism pattern caused by the interaction of light wave and free electrons in metals, can break the diffraction limit to realize the subwavelength photoelectric loop's integration. Along with the processing precision, the sub-wavelength photonic integration devices based on surface plasmon are widely researched at the basic theories and experiments. This article summaries SPPs' elementary theories and experiments, then carries on the subwavelength metal focusing lens' image analysis and optimization designs.The first part proposes the metal focus lens model (metal double-slit dielectric gratings modified structure), and analyses the impact of the double slits and the exit surface dielectric gratings' physical parameters on the transmission of light. First of all, considering metal focusing lens research, in particular with single-slit metal lens' problems, the advantages of metallic double-slit lens are elaborated; secondly, by use of waveguide dispersion, diffraction gratings and rigorous coupled wave theory, we obtained the physical parameters of SPPs effective refraction, the phase relationship of light and SPPs excited resonance angle.The second part optimally designs many kinds of methods about adjustments of focal length and focusing deflection, and points out their relative superiority. The adjustments of focal length mainly have 3 methods:1. the change of the middle medium column's width, compared with chirping surface medium gratings cycle of the metal single slit structure, reduces the medium processing number; 2. the change of surface medium gratings shape, may also realize the wide range adjustment of focal length; 3. the change of medium grating thickness' linear distribution, the biggest band reaches 1.16μm, which is bigger than 0.77μm for the metal groove structure, moreover metal coating is easier exactly processed than metal carving groove. And the adjustments of focusing deflection mainly have 2 methods:1. asymmetric change of the double-slit physical parameters (dielectric refractive index and slit width), particularly asymmetric change of refractive index obtains the maximum deflection angle of up to 25°, relative to asymmetric change of both side dielectric gratings' cycles, is easy modulated and processed; 2. the change of the rectangular beam's incident angle, can achieve a certain deflection angle in the focusing structure.