Study On The Principle And Fabrication Technique Of Metasurface Lens Based On Surface Plasmon Polaritons

With the rapid development and wide application of optical instrument technology,the traditional optical lens has become the technical bottleneck which restricts the system toward miniaturization,integration,arrays,lightweight direction.How to break through the technical bottleneck and start from the principle of in-depth study that can break the diffraction limit,realize micro-nano scale optical information transmission and processing,and develop the fabrication technology of micro-nano optical device,has very important scientific and realistic significance for integration and miniaturization of optical instrument development.In this paper,with the support of the National Basic Research Program of China(973 Program)and the National Natural Science Foundations of China,we deeply study the principle metasurface focusing lens and fabrication method based on surface plasmon polaritons(SPP).Aiming at the shortcomings of large and bulky volume for the traditional vector polarized light beam focusing system and the problems of expensive cost and low efficiency for fabricating metasurface,we carried out the following main research work:(1)First,we introduce and analyze the tightly focused vector beam with unique nature and broad application prospect.By making use of curved metal antenna and localized surface plasmon resonance to manipulate cross-polarization light and its phase,we designed an ultra-thin radially and azimuthally polarized metasurface lens.A tightly focused spot and a doughnut-shaped focus can be achieved at the wideband frequency range of 300THz-400 THz for radially and azimuthally polarized incident light,respectively.By introducing apodization factor,we can obtain the tight focal spot beyond the diffraction limit(0.47?).Compared with traditional lenses,metasurface lens have some advantages,such as ultra-thin thickness(?/20),aberration-free,easy integration and achieving super-resolution focus.(2)We propose a novel principle for directly converting and focusing the radially polarized(RP)light and design a metal-dielectric grating metasurface based on polarization filtering,which can simultaneously generate and focus the RP light for circularly polarized light illumination at visible light.By varying the period and duty cycle of Au-Si grating,we can manipulate the phase of TM(Transverse Magnetic)polarization and at the same time improve the transmittance of TM polarization and extinction ratio.Then by way of divided regions to locally control the polarization and phases,we can obtain the tight focused RP light.This directly converted metasurface lens has the advantage of large numerical aperture and ease of integration.Because the lens is no need of the liquid crystal polarization converters or spatial light modulator to generate RP light source,and no need of additional collimating system to keep the center of the beam and the lens coinciding,this greatly simplifies the optical system for traditional RP focusing.(3)Aiming at the problems of lacking of effective wavefront control devices in terahertz wave,we propose a metal-dielectric-metal-dielectric-metal multilayer unit cell,analyze the mechanism of electromagnetic resonance and coupling effect among the three-layer metal antennas and achieve efficient polarization conversion and wavefront control.Based on the principle of PB phase,we not only obtain anomalous refraction with high efficiency and large-angle,but also design a large numerical-aperture and efficient metasurface lens with good focus performance and thin thickness(?/5).Flat metasurface lens is convenient for application in miniaturized and integrated terahertz imaging and detection systems.Meanwhile it provides the theory basis for the design of other types and frequency band optical devices.(4)Aiming at the shortcoming of expensive cost and low efficiency for fabricating metasurface device,we proposed a high efficiency and low-cost method to fabricate metasurface device.By using reflective plasmonic Ag layer,surface plasmon imaging lithography can amplify and compensate evanescent wave,and then solve the problems of poor fidelity,low contrast,shallow exposure depth suffered from conventional near-field optical lithography.By optimizing exposure,development,etching process,we fabricated anisotropy nano-hole metasurface lens.(5)We build optical test systems and experimentally demonstrated the focusing performance of metasurface lens in visible light.The experimental results are in agreement with the simulation results.This plasmonic imaging lithography scheme has advantage of low cost and high efficiency because the traditional I-line lithography equipment and mercury light source are available,and the mask can be used repeatedly.