Research On Multiple Fano Resonance And Its Application In MIM-type Waveguides

Surface plasmon polaritons(SPPs)are electromagnetic wave modes with collective oscillations formed by the coupling of incident light and free electrons that are excited at the metal-dielectric interface and can propagate along the metal-dielectric interface.SPPsbased optical waveguide devices can overcome the limits of conventional optical diffraction and manipulate light at sub-wavelength sizes,which has attracted widespread attention in the field of nano-integrated optical devices.Among various SPPs-based waveguide structures,metal-dielectric-metal(MIM)type surface plasmonic waveguides(SPWs)have advantages such as compactness,ease of fabrication,and strong ability to confine the electromagnetic fields.Meanwhile,Fano resonance with sharp asymmetric spectral line can be excited in MIM-type waveguides with special cavity structures,and these unique advantages and optical properties have enabled the design and production of various MIMtype filters,sensors,all-optical switches,and other devices.In addition,Fano resonance based on SPPs is extremely sensitive to the size of the structures and the refractive index of dielectric medium,which can promote its application in different aspects.To broaden the application of Fano resonance based on MIM waveguide devices in different fields,various forms of MIM waveguide devices with multiple Fano resonances have been explored,and their potential applications in biochemical sensing,slow light devices and other fields have been investigated.In this paper,two kinds of new MIM-type SPWs with compact structure are proposed,guided by the theories related to SPPs,MIM-type waveguides,and Fano resonance.Based on the numerical simulations,the multiple Fano resonances characteristics supported by them are investigated,and the causes,the transmission properties as well as the application of refractive index sensing and the slow light effect of multiple Fano resonances are also systematically discussed.The main research contents of this paper are as follows:(1)A SPPs-based MIM-type waveguide consisting of a k-shaped resonator is designed,which can support triple Fano resonances.The physical mechanisms and parameter dependence behind the formation of multiple Fano resonances are investigated by analy zing the effects of changes in electromagnetic field distribution and geometric parameters on the transmission characteristics.In addition,refractive index sensing characteristics are investigated by varying the refractive index of the dielectric filled in the waveguide.The maximum sensitivity reaches 1250 nm/RIU and the maximum figure of merit(FOM)exceeds 4000.Finally,the slow-light effect is also investigated.And the results show that the maximum optical delay time and group index are about 0.05 ps and 9.23,respectively.(2)A SPPs-based MIM-type waveguide consisting of an X-shaped resonator is designed,which can support quadruple Fano resonances.The influence of the geometric parameters of the X-shaped resonant cavity on the multiple Fano resonances is studied in detail through numerical simulations.The results show that some of the geometric parameters can achieve independent modulation of the spectral profile,transmission intensity and position of the Fano resonances.In addition,the physical mechanism behind the Fano resonance is investigated in conjunction with the electromagnetic field distribution.The results in refractive index sensing show that the maximum sensitivity and FOM are1350 nm/RIU and 37720.80 respectively in the refractive index range of 1.00 to 1.10,while the maximum sensitivity and FOM are 1416.67 nm/RIU and 13256.88 respectively for the refractive index range of 1.31 to 1.37.At last,the slow-light effect of the designed waveguide device is investigated based on the abrupt change of the transmission phase.In conclusion,the two MIM-type waveguides we designed consisting of special resonant cavities have the advantages of simple structure,easy integration and fabrication,while supporting multiple Fano resonances.There results can provide some basic references for the design of MIM-type SPWs structures,which will also have potential applications in the fields of refractive index sensing,slow light effect,and photonic device integration.