Study Of Optical Switching And Digital Metasurface Based On Plasmonic Fano Resonance

Owing to its strong sensitivity to the local environment and changes in geometry,the plasmonic Fano resonance(FR)in subwavelength nanoscale metasurface structure can be applied for optical sensing,switching,slow light devices,etc.Moreover,it is of great scientific significance to realize flexible amplitude modulation and multiwavelength information transmission and processing in metasurface structure.In this thesis,we mainly explore the influence of geometric parameters of unit structure on the light transmission properties in ringparabolic sub-wavelength nanostructures and the polarization dependence of near-infrared FR under fixed structures and design a new type of micronano optical devices.The main works are listed as follows:(1)The light transmission characteristics of parabolic holes,ring holes,and ring-parabolic composite hole arrays are studied numerically by the finite-difference time-domain(FDTD)method.The results show that the near-infrared plasmonic FR in the transmission spectrum comes from the hybridized mode between the ring hole and the parabolic hole structure.It is further verified that the TCMT agrees well with the numerical simulation.The plasmonic FR profile in the transmission spectrum can be effectively controlled by adjusting the relevant geometric parameters of the ring-parabolic composite structure.In addition,when the unit structure is fixed,the amplitude response of FR in the transmission spectrum can be adjusted by changing the polarization direction of the incident light.(2)In this context,a novel compact dual-wavelength passive plasmonic optical switching can be accomplished at the telecom O-and Lbands with ON/OFF ratios being 21.98 and 15.96 d B,respectively.In particular,such polarization-dependent passive optical plasmonic switching can be served as a 1-bit digital metasurface,by adjusting the polarization direction of the incident light to manipulate the amplitude response characteristic of the transmitted spectra.Also,the digital metasurface can be extended from 1-bit to 2-bit,and the 2-bit digital metasurface can be encoded not only in two kinds of single-wavelength switchings but also in dual-wavelength switching simultaneously.The proposed metasurface device not only provides a flexible and easy way to manipulate light,but also reduces the system size and is easy to integrate,and does not need an additional pump light source and complex control circuit and power supply.Besides,our results open the avenue toward sensors,optical digital communication,modulators,and miniaturized wireless communication systems in the optical communication band.More importantly,this optically controlled metasurface can be more easily extended to the all-optical regions than their electronically controlled counterparts,which also holds great promise for wider applications.