Special Modes In Epsilon-near-zero Material Based Waveguides And The Excitation

In the interaction between electromagnetic waves and dispersive materials,whose dielectric constant exhibits strong dependence on the frequency of the electromagnetic waves,the light speed is frequency dependent.Such dispersive materials are not only naturally occurring,with the development of science and technology people also become capable of designing and preparing materials with desirable dispersive properties.In certain frequency range of electromagnetic waves,some dispersive mateirals have dielectric constant close to zero,and are therefore named epsilon near zero(ENZ)materials.The vanishing of dielectric constant allows the materials to have many novel optical phenomena rarely occurring to traditional natural materials,such as strong coupling,tunneling effect and so on.In recent years,researchers from the entire world are becoming more and more interested in epsilon near zero materials.Since epsilon near zero material itself shows a host of unique properties,nanoscale waveguides based on these materials are also attracting much attention.The wellknown Berreman mode,Brewster mode,and so-called ENZ mode are all rooted in such waveguiding structures.While Berreman and Brewster modes are leaky modes,ENZ mode is a bounded mode.The waveguiding mode of ENZ mode exists in nanostructured waveguides consisting of ENZ materials.In particular,around the working frequency of the ENZ materials,the novel mode supported by the waveguides is defined as ENZ mode.The current thesis will study this guiding mode in thin film based multilayer planar waveguides.Propagating in the ENZ materials implies that the ENZ mode has its electromagnetic fields almost completely confined in the ENZ material layer.Such intriguing features simulate us to study this novel guiding mode in thin film based multilayer planar waveguides.In the thesis we utilized local and nonlocal electromagnetic response theories,and firstly derived the dispersion equations for both situations.In the case of local theory,we considered isotropic and uniaxially anisotropic ENZ materials,and for the nonlocal studies ENZ material is assumed isotropic.After obtaining the dispersion equations,they are solved numerically and we discussed the dispersion curves of guiding modes.Particularly when the dielectric constant closes to zero,we analyzed the distribution of electromagnetic fields and concluded that at the presence of such special mode ENZ mateirals strongly enhance the light intensity.The last part of this thesis mainly studies how to excite this special waveguide mode based on ENZ material.Here we used finite element method(COMSOL Multiphysics)to simulate the excitation,and to discuss the influence of waveguides on the emission power of an electric dipole,which could be used to manipulate spontaneous emission rate.Studies on ENZ mode pave the way to very interesting applications.In particular,the relatively easy fabrication techniques of thin-film semiconductor waveguides lead to applications including directional perfect absorption,ultrafast voltage-tunable strong coupling with metamaterials,electro-optic modulation,ultrafast thermal emission and the control of quantum dot spontaneous emission.