Design And Regulation Of Optical Metasurfaces Based On Localized Resonance Effect

The optical metasurface based on the localized resonance effect is a kind of artificially constructed device with special functions that can respond to the external incident light.Localized resonance effect is the fundamental working principle of this kind of metasurface.Under the strong interaction between the light and the matter,the optical metasurface based on the localized resonance effect can precisely regulate the phase and amplitude of the incident electromagnetic wave,so that the scattering,reflection and absorption spectrum can be designed according to the required functions.And this process is usually accompanied by a strong field enhancement effect,which has important applications in display,energy and biology.Plasmonic metasurfaces and dielectric metasurface based on high refractive index materials are two important optical metasurfaces based on localized resonance effect,which have great value in application for biosensors,surface enhanced Raman scattering and surface enhanced fluorescence,optical lens,and structural color and so on.Reasonable design and regulation of the optical metasurface based on localized resonance effect can enrich its functions to adapt to more situations on demand.There are still some challenges in design and regulation.On the one hand,the existing metallic plasmonic metasurface has high loss,which will degrade the performance of the metasurface.On the other hand,the resonance properties of current optical metasurface can be adjusted by changing the materials,interval and period of the structure,which are mostly based on changing the in-plane coupling effect between the structure unit.The design and regulation of a metasurface with out-of-plane coupling effect that may provide stronger field enhancement and new degrees of freedom for regulation are yet to be developed.In addition,after finished the preparation of the metasurface according to the designed parameters,the structural units cannot be changed.Once the working wavelength is changed,the re-design and preparation of the complex metasurface will cost a lot of time and materials.It is very important to develop the structure and the way of adjustment with more degrees of freedom.In this theis,all-dielectric silicon nanoring metasurface based on high refractive index material and two-layered gold nanoribbons soft plasmonic metasurface based on the out-of-plane design are proposed,the preparation,characterization and regulation of which are studied.The thesis is carried out from the aspects of theory,simulation and experiment.The main content of the thesis includes:Firstly,all-dielectric silicon nanoring metasurface based on high refractive index material is designed,which can be used for structural color.Design and simulation of the silicon nanoring metasurface are studied.The localized resonance modes which can be excited in the silicon nanoring metasurface are also studied.We have studied the effect of four structural parameters on the reflection spectrum using simulation and experiments,which are outer diameter,inner diameter,the spacing between the nanoring structure unit and the thickness of the nanoring layer.It is shown that one electric resonance mode and two magnetic resonance modes can be excited in the silicon nanoring metasurface.The increase of the outer diameter can cause the red shift of the reflection spectrum,while the increase of the inner diameter can lead to the blue shift of the reflection spectrum.The effect of the spacing between the nanoring structural units on the reflection spectrum is relatively complex.With the increase of the spacing between the nanoring structural units,the electric response mode shows red shift,and the magnetic response mode can be split into two peaks from one peak.And among the two peaks,with the increase of the spacing between the nanoring structural units,the lower frequency magnetic response mode shows great red shift,while the higher frequency magnetic response mode shows a little blue shift.Through the reflection spectrum characterization of the metasurface and chromaticity diagram characterization of the color after chromaticity calculation,it is shown that the design can theoretically achieve a color gamut beyond the standard RGB range.Secondly,two-layered gold nanoribbons plasmonic metasurface based on the out-of-plane design is proposed.The design and simulation of the two-layered gold nanoribbons metasurface are discussed.The localized resonance mode which can be excited in the two-layered gold nanoribbons metasurface is also studied,and we compare the mode with its counterpart which can be excited in metasurface with in-plane design and similar structural unit.We have studied the effect of three parameters on the reflection spectrum using simulation and experiments,which are the period of the structure,the separation height between the upper layer nanoribbons and the lower layer nanoribbons and the incident angle of the light.It is shown that one electric resonance anti-bonding mode can be excited in the two-layered gold nanoribbons plasmonic metasurface.Compared with the excited mode in metasurface with in-plane design and similar structural unit,the localized resonance mode in out-of-plane designed two-layered gold nanoribbons metasurface can generate the largest field enhancement factor up to 1293,which is 32 times of that in metasurface with in-plane design and similar structural unit.As for regulation,the larger the period,the longer the wavelength.So with the increase of the period,the resonance wavelength in reflection spectrum shows red shift.With the increase of the separation height between the upper layer nanoribbons and the lower layer nanoribbons,the resonance wavelength also shows red shift.And the increase of the separation height weakens the out-of-plane coupling strength.When the incident angle of the light is increased,there is a redshift of the resonance wavelength in the reflection spectrum of the two-layered gold nanoribbons metasurface with out-of-plane design.Thirdly,the preparation methods of dielectric metasurface based on high refractive index on rigid substrate and two-layered gold nanoribbons metasurface on flexible substrate are explored.We have explored the method of fabricating the silicon nanoring metasurface in detail using traditional micro-nano processing technology.We have solved a series of problems in designing process parameters of achieving the silicon nanoring metasurface,including the size design of the e-beam lithography layout,the selection of the minimum resolution and electric dose during the electron beam lithography process,the selection of the development and fixing time and the selection of the etching depth and the length of etching time.The traditional micro-nano processing technology involving electron beam lithography requires the substrate surface should be flat and have a certain conductivity to reduce the gathering of electron beam and avoid affecting the accuracy of the resolution and the morphology of the metasurface.We propose a template method suitable for the preparation of out-of-plane coupling designed two-layered gold nanoribbons metasurface on flexible substrates,which cannot be prepared by traditional micro-nano processing technology.In this thesis,two kinds of metasurfaces and their optical characteristics were characterized by scanning electron microscope,atomic force microscope and reflection spectrum measurements.Fourthly,it is proposed for the first time to combine the metasurface based on the out-of-plane coupling design with the flexible material.And we have researched on the soft two-layered gold nanoribbons metasurface which is fabricated on PDMS soft substrate with out-of-plane design.We have studied the variation of the geometrical deformation of the structural unit of the metasurface under tensile strain using mechanical simulation.A simplified model is proposed to fit the morphology of the structural unit under tensile strain.The effect of tensile strain on the reflection spectrum are studied by simulation and experiments.It is shown that the tensile strain leads to the increase of the period and the decrease of the separation height between the upper layer nanoribbons and the lower layer nanoribbons.With the increase of the period,the resonance wavelength show red shift,which is the regulation of the in-plane coupling effect.With the decrease of the separation height,the resonance wavelength show blue shift,which is the regulation of the out-of-plane coupling effect.Tensile strain can regulate both coupling effects simultaneously.While under the competitive relationship,the period has a greater influence on the resonance wavelength in the reflection spectrum,which is obtained by the red shift of the resonance wavelength in the reflection spectrum in the experiment.In this study,the normalized resonance sensitivity of the metasurface was analyzed and found to be comparable to that of the current flexible metasurface.We have characterized the repeatable stretchability and one-year stability of the flexible metasurface of the two-layered gold nanoribbons soft metasurface.