Research On Wavelength Dependent Multichannel And Multi-Order Optical Vortices Based On Metasurfaces

Optical vortices(OVs)in the visible band,with helical phase wavefront and orbital angular momentum(OAM)of multiple eigenstates,have broad application prospects in the fields of optical information multiplexing and optical manipulation.The highly localized and uneven spatial distribution of the subwavelength light field in metal metasurfaces provides a promising means for the generation of OVs with arbitrary topological charges.When the coupling between the localized light field and the molecular exciton is strong enough,the energy level and radiation of the hybrid system will change,forming a new hybrid mode,which has important application value in quantum information processing,low threshold laser,molecular detection and other fields.The work of this paper focuses on the strong couplings of different mode light fields with the same type of J-aggregates in metal nano core-shell resonators,the generation of arbitrary order multi-channel OVs at visible light frequencies using metal metasurfaces,and the multifunctional applications of OVs on double-layer metal metasurfaces.The designed metal core-shell resonator provides new ideas for the tunable performance of optical devices and handling complex multimode strong couplings;the improved single-layer or double-layer geometric phase metal nanopore metasurfaces provide a simple and reliable solution for achieving ultra compact,low-cost vortex beam arrays,which helps to improve the capacity storage and security of optical communication,and possess great applications in beam shaping,optical tweezers,near-field detection,and super-resolution imaging.The main contents of our studies are as follows:1.The metal nano core-shell resonator system with ultra small mode volume has been constructed,which supports the strong couplings of two localized surface plasmon modes and molecular excitons.The multimode interference coupled mode theory(MICMT)and the finite difference timedomain(FDTD)method are used to study the mechanism of the coupling of J-aggregate molecules with different modes of localized light fields and the energy exchange rate in the two coupling systems.The Rabi splitting of 143.7 meV and anti-cross energy dispersion in the extinction spectrum are achieved.Research has shown that higher-order modes have smaller mode volume and stronger local field density,making it easier to meet the criterion of strong coupling.We have simulated and explored the effects of multiple structural parameters and different materials on the mode volume.We also have obtained the quantitative relationship between the coupling coefficient under strong coupling and mode volume with the number of excitons,as well as the relationship between oscillation frequency and coupling coefficient.This work has potential applications in the fields of quantum information and biosensors,and provides a new method for realizing the strong interaction between surface plasmon cavities and molecular excitons at room temperature.2.The single-layer metal nanopore metasurfaces are designed,and based on FDTD simulation and spin-to-vortex conversion theory,it is found that the overall effect of the geometric phases of multiple structural units on the metasurfaces is manifested as the spin-orbit interaction(SOI),generating near-field plasma vortices and far-field propagating OVs.And the influence of structural parameters on transmittance and geometric phase has been studied,achieving the generation and characterization of first to eighth order independent OVs.On the basis of the simulation model,the electric field pattern,propagation path,and phase of arbitrary order OVs are studied using the Laguerre-Gaussian(LG)beam theory,and the law of polygonal focal rings is also discovered.By controlling the parameters of the nanopore arrangement distribution,simultaneous amplitude and phase regulation of the vortex beam array has been achieved.The average signal-to-noise ratio of multi-channel OVs is above 15dB,meeting the requirements of multiplexing.In addition,using the orthogonality of OVs of different orders,a dual channel vortex beam generator with the same propagation direction is designed.The sixth order plasma vortex is obtained in the near field,and the second order OVs is obtained in the far field.This makes the OAM information and electric field distribution obtained in the near field different from those obtained in the far field,which helps to enhance information storage and encryption,and realize the application of super-resolution imaging.3.On the basis of the above work,we have expanded from singlelayer metal nanopore metasurfaces to double-layer metal nanopore metasurfaces,achieving an optimization of approximately 30%increase in transmittance and 8%increase in the induced phase efficiency.Propose a series of design solutions to achieve multifunctional applications of OVs:utilizing the characteristics of OVs being able to fully reflect and propagate in high refractive index fibers,achieve demultiplexing and beamforming of individual OVs;Utilizing the broadband and efficient advantages of geometric phase metasurfaces,achieve the focal ring and phase characterization of polychromatic OVs from 500nm blue light to 700nm deep red light;Using the multiplexing of OVs and the orthogonality of different orders,composite optical vortices(COVs)and multi singularity OVs are obtained.Then use the conservation of angular momentum and the conservation of the total mode density of the outgoing vortex beam carrying the OAM to generate additional channels of OVs,and design three multi-channel optical vortex coupling schemes to further increase the channel capacity and improve security.Finally,in order to achieve the application of multi well optical tweezers,the distribution of light radiation force and light gradient force generated by CO Vs on Rayleigh model dielectric particles was explored,which can achieve the capture and manipulation of microscopic particles.Our work of this paper has solved the important problems related to the research of light field and OAM,such as the strong couplings of complex mode light field and matter,the generation of arbitrary order vortex beams,the superposition of phase-controlled OAM,and the coupling of multi-channel OVs with the same order.These results have broad application prospects in the fields of applied optics,topological optics,and chiral quantum optics.