Research On Fano Resonance And Sensing Characteristics Based On Subwavelength Waveguide Structure

Due to the limitation of classical diffraction limit,the development of photonic devices has reached a bottleneck in size.Surface plasmon polaritons(SPPs)is a way to regulate light in the sub wavelength range.Its advantage is that it can break through the classical diffraction limit and bring hope for the integration of photonic device chips.Metal dielectric metal(MIM)waveguide has attracted extensive attention of scholars because of its small size,easy excitation and simple structure.Fano resonance is a mode interference effect produced in the ionic structure.Because it has the properties of asymmetric and sharp line shape and is sensitive to the change of refractive index,it can be applied in the fields of refractive index sensing and slow light.In recent years,graphene surface plasmons have become a research hotspot of scholars because of their special optical properties,adjustability and strong local effect of electromagnetic field.In this thesis,two different waveguide structures are designed and analyzed by using finite difference time domain(FDTD)method combined with coupled mode theory(CMT)and multimode interference coupled mode theory(MICMT).The main research contents of this thesis are as follows:(1)Firstly,a cross shaped rectangular cavity MIM waveguide structure is proposed,three Fano resonance peaks are realized,and the generation mechanism of Fano resonance in the structure is studied.The refractive index sensitivity of the structure is up to 1000nm/RIU,which can be used to construct refractive index sensor.Secondly,a rectangular cavity is added to the left of the cross rectangular cavity,and five Fano formants are obtained.Thirdly,a rectangular cavity is added to the right of the cross rectangular cavity to realize six Fano formants.Finally,the sensing performance and slow light characteristics of the composite structure are studied respectively.(2)Firstly,an L-shaped graphene strip structure based on graphene plasmon is proposed,which produces the phenomenon of plasma induced transparency(PIT)in the terahertz band.The formation mechanism of pit in the structure is explained by using the electric field energy diagram.Secondly,the function of optical switch is realized by changing the Fermi level,and the sensitivity obtained by changing the refractive index is up to 2.725THz/RIU.Thirdly,two additional pit windows can be generated by adding two L-type graphene strips of different sizes.Finally,the sensing performance of the composite structure is studied.