Study And Implementation Of The High-Q Resonances For Metasurfaces Applications

Robust development in nanostructure manufacturing capabilities allows us to design and fabricate metasurfaces that are capable of achieving efficient wavefront control of electromagnetic waves.It leads us to the new age of technologies and is comparable to control over a fire in ancient times.Thus,designing the metasurfaces as a fundamental part of different applications is important,particularly in implementing optical antennas,laser and sensor devices with outstanding characteristics.Metasurfaces made only by utilizing all-dielectric components are promising for optical applications due to their low dissipative losses and a great variety of supported resonances,in counterpart to plasmonic ones.However,realizing high-quality resonances in dielectric metasurface based on an open resonator（open resonant system）takes much work.Among a variety of known metasurface configurations,we distinguish a particular class of planar resonant structures that allow obtaining the strongest resonant response due to the excitation of so-called trapped modes（also known as the symmetry-protected bound states in the continuum,BICs）.The degree of this asymmetry introducer in the unit cell of the metasurface determines the strength of electromagnetic coupling between the incident field and the currents induced by this field on the constituent particles.In the context of light and matter interaction in a metasurface,the additional problem for high-quality resonances appears.It is due to the field localization inside the resonator’s volume.It can be overcome by the clever design of cluster-based metasurface,which is discussed in these theses.1.Herein,we study realistic dielectric metasurfaces composed of a large but finite number of resonators.In the first stage,we obtain an approach for calculating the coupling coefficients between dielectric resonators located in free space.We derive our approach in a general form,considering the arbitrary mutual orientation of resonators in free space,and compare our analytical results to numerical simulation.Additionally,we provide simplified equations suited to use for engineering purposes.Finally,we utilize our method to study the characteristics of all-dielectric antennas with non-planar and free-form disks configurations.The antennas with bidirectional radiation patterns and beam steering capability are realized.All results are verified in full-wave numerical simulations and quasi-optic experiments.2.The metasurfaces that support high-Q resonances based on asymmetry breaking are characterized.The origins of high-Q resonances are based on the symmetry breaking of properties of the TE_01δmode of a single resonator（with axially symmetric electric oscillations in the plane）arranged in a periodic 2D array.The unit cell symmetry breaking with the assistance of natural material anisotropy（the anisotropic properties of bulk Mo S₂）,artificial anisotropy（spatial asymmetry）,and artificial anisotropy with coupling in cluster unit cells are examined.The use of cluster-based metasurface unit cells allows exciting different dynamic out-of-plane magnetic dipole orderings FM and AFM.The metasurface designs with polarization insensitivity and field localization outside of high-index resonators are also realized.All designs of proposed metamaterials that support the excitation of the high-Q resonant trapped mode regimes are characterized in full-wave numerical simulations and experimentally verified.3.Due to the duality of the electromagnetic phenomena,we show the designs of the metasurfaces that support high-Q resonances,where the origins of high-Q resonances are based on symmetry breaking of properties of the hybrid mode of the trimer（with axially symmetric magnetic oscillations in the plane）,arranged in a periodic 2D array.Particularly,this hybrid mode oscillation corresponded to the excitation of the toroidal dipole mode.In trimer-based metasurface,we examine the different in-plane and out-of-plane symmetry-breaking mechanisms for toroidal dipole mode excitation.In addition,the trimer-based metasurface with different unit cells is studied.Using trimer-based cluster metasurface’s unit cells allows exciting different dynamic out-of-plane toroidal dipole orderings TO and ATO.The metasurface designs with near-field hot spot control via polarization and field localization outside of high-index resonators are realized.All designs of proposed metamaterials that support the excitation of the high-Q resonant are characterized in full-wave numerical simulations and experimentally verified.After tunning metasurface’s frequency in a range of interests,presented in this thesis,designs of high-Q metasurfaces with plasmonic-like near-field localizations are recommended as a platform for sensory applications and lasing devices,like SPASER（Surface Plasmon Amplification by Stimulated Emission of Radiation）.