Research On The Design And Characteristics Of Hyperbolic Metamaterials For Micro/Nano Optical Imaging

The emerging discipline of biomedical photonics is developing rapidly,and there is an urgent need for micro/nano optical imaging technology that can obtain cell and tissue information.The development of nanoelectronics and nanophotonic devices also requires disruptive lithography.These are bound to rely on super-resolution imaging that can break through the diffraction limit,but there are still considerable technical difficulties in breaking through the diffraction limit.In recent years,the emergence of hyperbolic metamaterials has greatly pushed micro/nano optical imaging beyond the diffraction limit.The extraordinary open dispersion curve characteristics of hyperbolic metamaterials allow evanescent waves to be reconstructed in the far field,thus achieving super-resolution imaging,and therefore attracted much attention.At present,obtaining higher imaging quality,smaller resolution imaging,and expanding from 2D imaging to 3D imaging are research hotspots in the field of micro/nano optical imaging.However,there are still some problems such as the two image points will interfere with each other,resulting in the deterioration of imaging quality,the lack of radial resolution accuracy in 3D imaging,and the specific structure can only improve the single imaging quality.We design a new type of hyperlens structure that introduces a nano-gap layer in this paper.The basic unit is first composed of a metal and a specific refractive index dielectric film,and then a tubular 3D structure is constructed from the basic unit.The device has a simple structure and is easy to process and prepare in the future.The device structure can use hyperbolic metamaterials to excite the surface plasmon polaritons to break through diffraction limit imaging.Under the condition of sacrificing a certain far-field imaging focal position,it can reduce image interference and improve imaging quality compared with traditional hyper lens.The radial resolution of 3D imaging is greatly improved,and the advantages of various other imaging characteristics are improved.The main work and results of the thesis are as follows:(1)Using 10nm thick silver(Ag)and 10nm thick yttrium trioxide(Y2O3)as the basic unit,a traditional 2D flat-type hyperlens was constructed,which was then successfully extended to 3D hyperlens.Finite element simulation shows that the 3D microtube hyperlens composed of 92 period basic units(inner diameter 400nm,outer diameter 2240nm)can separate the images formed by two 365nm point light sources with a horizontal distance of 180nm in the far field.The position of the focal point in the far field is 355nm away from the outer wall,and a radial resolution of 20nm that is far less than half a wavelength is also obtained,thereby achieving micro/nano 3D imaging that breaks through the diffraction limit.The simulation also found that there are side lobes near the image points of the two point light sources.Therefore,a new physical quantity used to evaluate the imaging quality of the hyperlens breaking through the diffraction limit is defined which called side lobe suppression ratio.The side lobe suppression ratio of the 3D microtube-type hyperlens is 4.82dB by the calculation formula.(2)On this basis,by introducing a nano-gap layer into the 3D microtube-type hyperlens structure,the imaging quality of breaking the diffraction limit is improved simply and efficiently.After systematically optimizing the number,refractive index,thickness,and position parameters of the nano-gap layer,the following is obtained:the nano-gap layer is single layer,the thickness is 30nm,and the interior is kept under vacuum.The distance between the initial position and the inner wall of the tube is three basic units(60nm).(3)The wave vector method was used to theoretically explain the reason for the change in the far-field focal position and side lobe suppression ratio of the optimized 3D microtube-type hyperlens with the introduction of the nano-gap layer.Subsequent finite element simulations showed that:compared with traditional 3D in the microtube-type hyperlens,the introduction of the nano-gap layer only at the cost of the far-field focal position shrinking to 216nm from the outer wall,which increased the radial resolution of 3D imaging by 85%,reaching the level of 3nm for the first time;meanwhile,the side lobe suppression ratio is increased by 3.95dB to 8.94dB,and the mutual interference between the two image points due to the side lobes is reduced to at least half,thereby improving the imaging quality.