Research On Two-dimensional Periodic Photonic Device With Subwavelength Structure

Surface Plasmon Polaritons (SPPs) is a kind of excited state formed by the interactionsbetween photons and free electrons on the surface of the metal. It can confine the light spread insubwavelength structure, overcome the diffraction limit and greatly reduce the size of photonicdevices. SPPs have many prominent features such as ultra-high resolution imaging, transmissionenhancement, subwavelength constraint and so on. So SPPs is potential in nano optical imaging,new efficient light source, biosensors and other related fields.Based on the summarization of the basic theory of SPPs, thesis researches a kind of SPPsfocusing lens with metal-dielectric annular slit structure, mainly focus on the following questions:We select a set of more appropriate structure parameters by computational analysis, use finitedifference time domain method for numerical simulation. As the focusing performance of the singlemetal-dielectric annular slit structure is not good, multiple metal-dielectric annular slits structure isdeveloped, the relationship between the focusing properties and the number of slits is studied,changes the slits number within the range from1to6, the focal length may change between1.25μmand1.75μm, the depth of focus may change between1.1μm and2.2μm, the FWHM may changebetween228nm and300nm, the focusing effect is very good.In the structure with three periodic slits, the influence on the focusing properties of the innerring radius and the interval of the slits is studied, when t=0.5μm, change r from0.2μm to2.5μm, thefocal length may change between0.75μm and2.75μm; when r=1.0μm, change t from0.4μm to0.7μm, the focal length may change between1.05μm and2.95μm.Changing the incident angle of the light source may produce a certain deflection of the focalposition, when the incident angle changes from0to30°, the deflection angle may change from0to49.63°.The focusing efficiency is improved by adding the periodic groove structure, the field strengthat the focus point is2.5485v/m, which increases33%relative to the structure without periodicgroove structure.Compared to traditional optical focusing lens, the main advantages of the focusing lensdesigned in this paper is its small geometric dimensions, ease of integration, it provides a reference for the early realization of subwavelength focusing in the field of imaging.