Study On The Characteristics Of Fano Resonance And Mode Splitting In MIM Type Plasmonic Waveguides

Surface plasmon polaritons(SPPs)are a kind of collective charge oscillation,resulting from the coupling between the input light and free electrons of metals.The SPPs wave can propagate along the interface between metals and insulators;however,it will decay exponentially on the both side directions of the interface.SPPs have extremely small mode area,which can break the limitation of diffraction limit to propagate and manipulate the electromagnetic field at subwavelength scale.In terms of the unique characteristics,SPPs have been considered as excellent carriers of energy and information,providing a new thought towards nanoscale optical devices in realizing various functions.Consequently,SPPs based on surface plasmonic waveguides(SPWs)have become a hotpot that attracts people's attention in the area of integrated nanoscale optical devices.Metal-insulator-metal(MIM)type SPWs structure,with the excellent characteristics of easy excitation of SPPs,easy fabrication of structures,mature processing technology,strong confinement of electromagnetic fields,longer propagation distance,and lower coupling loss,has gradually become the preferred choice on the design of SPWs devices.In recent years,many MIM type SPWs devices have been designed and studied to achieve different functions.Based on the reported studies,this paper will design and study two kinds of novel SPWs devices based on MIM type structure with numerical simulations and theoretical derivations.Both of the two structures can achieve PIT-like transmission characteristics.The main research contents of the thesis are as follows:(1)A kind of MIM type SPWs structure is designed,which is composed of a bus waveguide with a stub resonator coupled to a split square ring resonator.By using finite element method(FEM)method,the transmission characteristics of the structure are analyzed numerically.In addition,the temporal coupled mode theory(CMT)is used to analytically fit the numerical results to give a comparison and to verify the accuracy.The dependence of the transmission characteristics of the designed SPWs device on the geometric parameters is studied in detail by changing the geometrical size such as height of the stub,size of the split ring and by changing the symmetry of the structure.At the same time,by calculating the position change and the intensity change of the resonance peak caused by the change of the refractive index of the medium inside the cavity,the application characteristics of the device in the field of refractive index sensors are studied.It is found that the device can achieve higher sensing performance with sensitivity up to 1500nm/RIU,which will have great application prospects in the field of nanoscale refractive sensors.(2)A type of SPWs structure with plasmon induced absorption like(PIA-like)transmission characteristics based on MIM structure is designed.The waveguide structure is consisted of a straight bus waveguide directly or indirectly coupled with two ring resonators.Studies have shown that this type of PIT-like transmission is formed by the resonant mode splitting induced by field-driven interactions between the two ring resonators.Simulation results also indicate that this mode split is not only sensitive to changes of geometric dimensions,but also affected by the refractive index of the medium filled inside the resonators.In addition,the group index can be a larger positive or negative value at a certain wavelength,which means the normal and abnormal dispersion characteristics,and can achieve slow-and fast-light effects,respectively.The designed structure can not only realize functions such as nanoscale filtering and nanoscale refractive sensing with sensitivity of 685nm/RIU,but also provides a new idea for the control of light speed.