Research Of High Q-Factor Sensors Based On All-Dielectric Multi-Fano Resonances

In the field of micro and nano optics,all-dielectric metasurface have become a hotspot in recent years due to their low ohmic loss advantage that metal metasurface do not possess.In particular,all-dielectric metasurface can inspire multiple coupled electromagnetic sources under the incident electromagnetic waves,which can excite high Q-factor(quality-factor)multi-Fano resonance.This characteristic makes them widely used in absorbers,nonlinear optics,sensors,and so on.In this paper,we focus on the study of all-dielectric metasurface that can excite high Q-factor multiFano resonances and apply them to the field of high preformance refractive index sensing,with the following aspects.1.We designed a metarsurface consisting of two Si-based semicylinder and proposed a sensor with the sensitivity of 365 nm/RIU and FOM(figure of merit)of 3550 RIU-1.Symmetry-breaking method is used to produce double Fano resonances with Q-factors of 535 and 19998 under the incidence of incident wave on the metasurface.The far-field radiation properties of resonant modes are investigated by Cartesian multipole decomposition technique,and the existence of multiple elementary electromagnetic sources such as toroidal dipole is confirmed in combination with the near-field distribution of metasurface.The existence of symmetry-protected BICs(bound states in the continuum)is demonstrated by verifying the inverse relationship between the Q-factor and the asymmetry degree.Moreover,the dependence of the transmission spectra on different geometric parameters is investigated as well to explore the optimal parameters of this metasurface for practical sensing applications.2.By designing a double hollow-strips Si-based cylinder dielectric metasurface,we proposed a sensor capable of generating double Fano resonances with the sensitivity of 160 nm/RIU and the FOM of 575 RIU-1.The metasurface exhibits Fano resonances which can be characterized by toroidal dipole response and magnetic dipole response,respectively.Then our metasurface shows excellent flexibility by verifying the geometric parameters.Comparing with similar previous studies,it is noted that double Fano resonances both exhibit good sensing performance while providing ultra-high Q-factors of 17106 and 8428,respectively.And this type of sensor does not suffer from the problem of overlapping detection points.The results of this study are important for future high-precision sensing applications.3.By designing a hollow split-ring silicon metasurface,we proposed a high-precision refractive index sensor based on multi-Fano resonances.This metasurface can excite six high Q-factor Fano resonances by symmetry-breaking,with the highest Q-factor up to 12787.Cartesian multipole decomposition technique is used to calculate the polar moments of elementary electromagnetic sources,and the multipole coupling modes are found at the resonant wavelength of the Fano resonances.Besides,the specific coupling is analyzed by the electromagnetic field of the metasurface.After that,we selected three structural parameters,including silicon film height,cell size and inner-radius of the split ring,to investigate the tunability of this metasurface in detail.The sensitivity and FOM of the six Fano resonances are different,with the highest sensitivity and FOM of 424 nm/RIU and 615 RIU-1,respectively.Since the hollow split-ring silicon metasurface can excite more Fano resonances than most of the proposed similar metasurfaces,it is believed that the results of the study can offer an excellent prospect for the study of refractive index sensing with multiple Fano resonances.