The Study Of Fano Resonances In Micro-nano Photonic Structures And Their Mechanism

The asymmetric lineshape Fano resonance is a quantum interference phenomenon generated by the interaction between discrete and continuous states,which is generally considered to be a special feature of quantum systems.However,the phenomenon of wave interference is also widely observed in classical optics,Therefore,Fano resonances have been extensively studied in various optical systems,such as plasmas,photonic crystals,topological photonic structures,and metamaterials.The asymmetric lineshape and high dispersion exhibited by Fano resonances make them have great application prospects in lasers,sensors,nonlinear and slow-light devices.In this thesis,we investigate the excitation mechanism,unique optical properties,and related optical applications of Fano resonances in different micro/nano-photonic structures,utilizing simulation calculation methods such as the finitedifference time-domain method and finite element method,together with theoretical analysis approaches such as the coupled mode theory and rigorous coupled wave theory.The main contents of this thesis include the following aspects:1)Considering the generally low-quality factor of Fano resonance in micro-and nano-structures of plasmas,a hybrid structure allowing for the coupling between graphene surface plasmons and Tamm states was constructed,taking into account the tunability of optical response of graphene surface plasmons and the strong light localization ability of Tamm states.The Fano resonance in this structure shows a high-quality factor and its lineshape and resonant frequency can be actively tuned.The physical mechanism of the Fano resonance was intuitively analyzed using dispersion relations and field distributions.The slow light characteristics of Fano resonance in the structure were also studied,and the sharp changes in amplitude and phase of Fano resonances bring about a high group delay,providing reference for the design of new high-performance slow light devices.2)According to the decoupling properties of Fano resonances,a selfreferenced refractive index sensor based on Fano resonances was designed by utilizing the grating-coupled graphene/waveguide structure.The optical transmission characteristics of the structure were studied using the finite-difference time-domain method and the rigorous coupled wave theory.The results showed that the resonant wavelength and the lineshape of Fano resonance in the structure can be respectively controlled by the incident angle of light and the Fermi energy of graphene.When the Fano resonance was adjusted to a symmetric line shape,the absorption characteristics of the structure were investigated,and a dualchannel high-performance absorber was achieved.When the Fano resonance was adjusted to an asymmetric line shape,the sensing characteristics of the structure were studied,and the results showed that the Fano resonance-based sensor has high sensitivity and self-referencing characteristics.This structure provides a certain degree of guidance and reference for the application of multi-channel absorbers and selfreferenced refractive index sensors.3)Focusing on the fact that narrow spectral line width and high spectral contrast of Fano resonances can greatly increase the modulation depth of optical switches,a Fano resonance based on the coupling between the graphene plasmon and the one-dimensional topological edge state was designed to achieve ultra-high-performance optical switches.The physical mechanism of the Fano resonance generation was analyzed using dispersion relations and electric field distributions.The tuning effect of Fermi energy of graphene and incident angle of light on Fano resonances were investigated by numerical simulation and theoretical analysis.The results showed that the lineshape and resonant wavelength of Fano resonances can be actively tuned by the Fermi energy and incident angle.By angle modulation,an optical switch with high modulation depth was realized,providing a new solution for the design and implementation of optical switch devices.4)Considering that the essence of Fano resonances is the interference effect of two modes,and the asymmetric line is easy to be affected or even destroyed by the change of geometric structure,a structure is designed to excite the Fano resonance by multi-cavity side coupling the topological waveguide.The generation mechanism of Fano resonances in this structure was analyzed using coupled mode theory.The sensing characteristics of the structure were also studied,and the rapidly changing amplitude of the Fano resonance makes the intensity-modulated refractive index sensor highly sensitive.By introducing defects such as disorders and impurities into the system,the stability of the system is studied.The results show that the Fano resonance in the structure still exists after the introduction of defects,and the structure still maintains high sensing performance.In order to further improve the stability of Fano resonances and the ability to resist structural manufacturing errors,a topological ring cavity and a topological corner state side coupling topological waveguide structure were also constructed.The existence of continuous and discrete states is ensured topologically,and the topological Fano resonance is realized after coupling.By introducing defects such as disorder,missing,and bending into the structure,it was found that the Fano lineshape can be maintained even in the presence of defects,demonstrating the robustness of the system.Therefore,these structures provide new schemes for the implementation of micro-nano photonic devices such as sensors,lasers,and optical switches based on Fano resonance.Graphs: 53,References: 243...