Study On Far Field Super-resolution Imaging And Subwavelength Focusing

With the deep research on nanometer scale technology and life science, the diffraction effect that limits the resolution of focusing and imaging in far field is becoming a fetal barrier to super-resolution in the domain of optics, for example optical microscopy, microlithography, optical data storage and etc. In order to obtain a higher resolution in far field, the diffraction limit should be conquered or circumvented by means of some special methods to make evanescent components contribute to the far field focalization or imaging with super-resolution. The surface plasmon polaritons (SPPs) with particular features of such as shorter wavelength than the incident light of excitation, surface localization and near-field enhancement provide a great idea to surpass the diffraction limit and attract more and more attention in related research fields. Based on the sub-wavelength metallic structures, the lens models of far-field sub-wavelength imaging and super-focusing were proposed and the principals were studied in this dissertation. It is observed that the elaborate structures were designed to manipulate the SPPs so that the sub-diffraction-limit imaging and sub-wavelength focal spot could be formed in far-field beyond the resolution limit.As the thickness of the mask, the oblique incident angles and polarization of the incidence wave were ignored when the scale diffraction theory was applied to calculate the aerial image in the traditional lithography simulation system, there was a great error between the prediction and the actual results transferred from mask to the wafer. The rigorous vectorial electromagnetic theory should be utilized and we exploit the waveguide method to acquire the near field distribution of the three-dimensional (3D) mask with off-axis illumination. A general 3D mask model with respect to the incident angles and the thickness of the mask is derived, which is convenient for aerial image calculation in the simulation of the sub-wavelength lithography fast and precisely. The shadow effect and the polarization effect induced by oblique illumination are illustrated by the numerical method. Furthermore, one of the resolution enhancement technologies, optical proximity effect correction (OPC), combined with the general 3D mask model are verified by related simulations. It was found that the OPC process can amend the near field distribution and enhance the final resolution of the project lithography. Also the optimal incident angles have been obtained by the numerical method, which are consistent with the actual value in practices.Based on the principle of cylindrical hyperlens, which was made of metal-dielectric alternating multilayer and could distinguish sub-wavelength objects in the far field beyond the traditional diffraction limit, we further optimized the structure of the hyperlens for lithography working at 193nm wavelength. The materials of the metal and the dielectric were replaced by aluminum (Al) and titanic oxide (TiO2) and they exhibited strong anisotropic with hyperbolic dispersion relation, which is propitious to shrinking imaging in far-field. The simulation results show that the 20nm technology node and below can be realized by the optimized hyperlens banding together with the phase-shifting mask,. This scheme can extend the life of the expensive 193nm lithography machines and supply a new precept for nano-scale manufacture.Although the cylindrical hyperlens is capable of magnification or demagnification, the curved inner and exterior surfaces have serious disadvantages on object location and image measurement. While the slab superlens has planar surfaces but cannot magnify or demagnify the image. Combined with the advantages of the planar Superlens and the cylindrical Hyperlens, we had put forward a Concave Hyperlens model, which provided with planar object plane and image plane for ease of usage and measurement, and is capable of shrinking or enlarging the image beyond the resolution limit. The electromagnetic propagation behavior via the multilayer of concave hyperlens has been derived rigorously with the transfer matrix method (TMM). Also the Mathieu functions have been introduced into TMM to study the field propagation in the confocal elliptical coordinate system and the semi-analysis expression for the transmitted field was deduced. The results of numerical calculation demonstrated that the concave hyperlens had demagnification imaging performance with high image contrast. Compared with multilayer planar superlens and planar hyperlens, our concave hyperlens takes on a distinctive non-uniform demagnification ratio.In order to focus the incident light in far-field with a high efficiency, we brought forward two kinds of nano-focusing schemes based on annular metallic lens with radially polarization illumination. One scheme shifted the near-field focal spot to far field by the modulation of the surface dielectric grating upon the exit plane of the metallic lens. The other one was based on radiationless electromagnetic interference (REI), through the anisotropic metamaterials adjacent to the exit plane of the metallic lens; the evanescent waves are amplified and converged in far-field to form a sub-wavelength focal spot efficiently. Taking advantage of the full wave simulation, we studied the first scheme of far-field sub-wavelength focusing in details and the parameters of the lens structure are optimized through numerical method. The simulation results showed that the far-field sub-wavelength focusing lens has a high focusing efficiency and figures of merit. Further the method to adjust the focal length by changing the annular slits'parameters or the numbers of grooves has been discussed, which are flexible to meet the practical applications.On all accounts, the overall results of this thesis illustrate that the proposed sub-wavelength metallic structures for far-field super-resolution imaging and the super-nanofocusing can conquer the traditional diffraction limit. The related study on super-resolution imaging and sub-wavelength super-focusing has great theoretical and practical value and is potential for nanometer manufacture technology, optical lithography, high density data storage, biology sensor, new type optical source, analysis and detecting technology and so on.