Multiple Fano Effects And Optical Sensing Properties Based On C3 Symmetric Metasurface Structures

Surface plasmon is a collective oscillation effect caused by the excitation of free electrons on the surface of a metallic structure by incident light when it interacts with a subwavelength metallic nanostructure.Metamaterials are two-or three-dimensional periodic structures composed of metals or dielectric materials that can precisely modulate light-matter interactions at the nanoscale.Two-dimensional optical superconfigurable materials,also known as metasurfaces with subwavelength periodic unitary structures,have attracted extensive research interest because they are ultra-light,ultra-thin and easy to integrate.By adjusting the geometric parameters of unit cells of metasurdace,such as shape and size,flexible modulation of optical frequency electromagnetic waves can be realized in the metasurfaces structures,including Fano resonance,optical switching and optical sensing.Fano resonance is an optical interference phenomenon that has been widely studied in light-matter interaction systems.The Fano resonance effect in metallic nanostructures can be produced by the interferometric interaction of plasmonic resonance modes with narrow linewidths（dark modes）and plasmonic resonance modes with wide linewidths（bright modes）.Interestingly,the multiple Fano resonances effect in the spectral response not only contain a local field enhancement effect at multiple wavelengths,but also help to realize applications such as nano-integrated circuits and multi-element biosensing based on this effect.In this paper,we investigate the optical response properties of a composite metasurfaces structure consisting of concentric C3 symmetry holes and circular hole unitary structures with tunable multifano effect and self-referential optical sensing phenomena by changing the C3 structural symmetry.The main contents are as follows.（1）In order to investigate the effect of C3 symmetry unitary structure in the metasurfaces structure on the realization of Fano resonance,we designed the tip C3 symmetry hole metasurfaces structure,the circular metasurfaces structure,and the composite unitary structure metasurfaces structure composed of both,respectively.The results show that when the incident light polarization direction is along the X-axis,the metasurface composed of the tip C3（circular）unitary structure alone induces an effective electric dipole resonance mode D_C3(D_CRA).When there is a spectral overlap between D_C3 and D_CRA in the near-infrared band,the two are able to produce triple Fano resonances phenomena in the composite metasurfaces structure through dipole interactions.Meanwhile,the multimode interference coupling mode theoretical analysis agrees well with the numerical simulation results.On this basis,we change the parameters of the tip C3 structure as well as the circular parameters,which can realize the modulation between single Fano resonance and double Fano resonance,triple Fano resonance,radiation monitoring sensing of the Fano depression depth and self-reference sensing with a single Fano resonance peak as the signal.（2）To further investigate the effect of the C3 symmetry unit structure on the multiple Fano resonance effect in the metasurfaces spectral response,we designed a composite metasurfaces structure consisting of a rectangular C3 symmetry hole and a circular ring.The results show that the rectangular C3-circular structure is also capable of producing triple Fano resonance phenomena when the incident light polarization direction is along the X-axis direction.By changing the polarization direction of the incident light,the modulation of the multiple Fano resonance effect can be realized.By changing the arm length of the rectangular C3 structure while keeping the polarization direction of the incident light along the X-axis constant,we can achieve the modulation between the double-Fano and triple-Fano resonance phenomena that are not the same as the tip C3.When changing the arm length of C3,plasmonic sensing phenomena can be generated.And then,by changing the inner radius of the circle,we can also achieve the modulation between multiple Fano resonances while keeping the parameters of the rectangular-C3 structure and the polarization direction of the incident light constant.