Investigation On Multiple Fano Resonances Based On Metasurfaces And Their Sensing Performance

It has always been the goal for the researchers to flexibly and efficiently control electromagnetic wave.Bidimensional synthetic material metasurfaces perfectly fit this demand.Metasurfaces are small,thin and easy to integrate and systematize,and it costs little to manufacture them.These advantages lead metasurfaces to shine in the applications such as invisibility cloak,high-performance sensing,super-focusing lenses,optical filtering and so forth.Recently,Metasurfaces exciting multiple Fano resonances have become a research hot issue in Optics.Due to the strong restricting ability of metasurfaces to the electromagnetic field,Fano resonances possess high Q-factor and narrow linewidth,which can provide a new solution for numerous high-performance optical applications,such as refractive index sensing.It is requisite for refractive index sensors to feedback the weak change information of the surroundings in order to offer the basis for medical diagnosis and environmental monitoring and other scenes.Metasurface sensors based on multiple Fano resonances can provide multi-channel sharp and highly sensitive observation resonances,Meanwhile,the sensing system is integrated on the chip,improving the detection efficiency and accuracy.In this paper,the finite difference time domain method and bound states in the continuum theory are utilized to explore the metasurface exciting Fano resonances and their characteristics,and analyze its application potential in sensing.The main four aspects covered in the whole paper are listed below.(1)A metasurface based on a rhombus-like etching hole is designed,and triple Fano resonances with high Q-factor are excited in the transmission spectrum by breaking the in-plane symmetry of the structure.The far field scattering intensity proves that the Fano resonances possess magnetic dipole and electric quadrupole characteristics.The proposed metasurface is extremely sensitive to the incidence polarization,and when the incident light with the polarization angle of 0° or 90°,different resonant excitation modes are presented in the transmission spectrum,which provides a novel scheme for bidirectional optical switching.(2)A butterfly-shaped metasurface is proposed.After introducing asymmetry break,the bound states in the continuum are transformed into the leakage modes,resulting in quadruple Fano resonances with narrow linewidth excited in the near infrared spectrum.Magnetic dipole,electric quadrupole,and toroidal dipole contribute dominantly,which indicates that the Fano resonances own richer modes.Fano resonance responses can be regulated through adjusting the structural parameters to meet different application requirements.With the help of near field coupling of adjacent unit cells,an electromagnetically induced transparency-like peak is excited,and the group refractive index is 145,and the sensitivity is 338.4nm/RIU,showing excellent slow light characteristic and sensing performance.(3)The narrow band absorber is formed by adding an aluminum layer under the metasurface with a rhombus-like hole.Triple absorption peaks with narrow linewidth are excited.The narrowest linewidth is 0.54nm,and the highest absorption rate reaches 99.7%.The linewidth of the absorption peaks can be tuned flexibly through changing the thickness of silica.The absorber features high sensing performance with the maximum sensitivity of 254 nm/RIU and the maximum FOM of 403 RIU-1.(4)Three substrate etching sensing optimization schemes are proposed on the metasurface with a butterfly-shaped hole.After optimization,the maximum sensitivity reaches 491.5nm/RIU,and the maximum FOM reaches 891.6 RIU-1.The two sensing measurement index increase 44.7 nm/RIU and 78.4RIU-1 respectively.