Research On All-dielectric Toroidal Dipole Metasurfaces And Devices

Understanding the physical mechanism of light-matter interaction and building novel devices for effective manipulation of light is one of the central problems in current nanophotonics research.The large amount of local electromagnetic field enhancement,high sensitivity to environmental perturbations,and high Q-value lineshape of toroidal dipole resonance make the All-dielectric toroidal resonant structures an important way to develop advanced nanophotonic components with low loss and low cost,and it has a strong potential to control light-matter interactions in various multiscale subwavelength photonic devices.As a fundamental member of the toroidal family,radiating toroidal dipoles are able to achieve strong squeezing of the field at very small points and effectively interact with incident electromagnetic waves.This is important for the study of resonant metastructures for applications such as low-threshold lasers,optical sensors,slow light,beam control,and chiral mediums.Toroidal dipole resonances excited in three-dimensional and two-dimensional metamaterial structures can be used for different purposes.For example,their powerful ability to confine incident optical radiation can be used in nonlinear optics.In the near-infrared band,this research includes the implementation and modulation of high-Q multi-resonance modes in a Alldielectric metasurface device,as well as the sensing performance and application analysis of this structure and its four extended structures.The specific research results are as follows.(1)A silicon block array metasurface structure based on quadrupoles is investigated in this work.It is capable of producing four high-Q Fano resonance responses driven by a toroidal dipole,an electric quadrupole and a magnetic dipole in a continuous near-infrared band with a theoretical maximum Q value of 2.0×106.Among them,the toroidal dipole resonance is doubly insensitive to polarization and fabrication tolerances.When inplane symmetry breaking is introduced,two symmetry-protected quasiBIC resonances driven by electric quadrupole and magnetic dipole,respectively,are excited.Then,the deep relationship between the structural asymmetry and the Q values of these two symmetry-protected BIC Fano resonances is analyzed and demonstrated.Finally,the dominant role of multipoles in the four modes,as well as the excitation of the nonradiative anapole state,is demonstrated by multipole decomposition and near-field analysis.(2)In terms of device analysis,firstly,the sensing performance of the device structure under the incident light polarization angle and refractive index of the surrounding medium is analyzed,and the double toroidal dipole resonances excitation of the device is demonstrated by multilevel decomposition.Then,an improved asymmetric metasurface structure was designed to achieve an ultra-thin and high Q value all-dielectric ultranarrow-band absorber.Finally,the sensing performance of four such extended metasurface structures is designed and analyzed,and the commonalities and differences of such all-dielectric metasurface structures are summarized.Compared with other complex nanostructures,the alldielectric supersurface structures studied in this work are more tunable and practical,which can be applied to near-infrared biological and chemical sensing,multi-channel refractive index sensing,optical switches and optical modulators,and provide ideas for the design of toroidal dipole devices with polarization-independent properties.