Generation And Manipulation Of Surface Polaritonic Vortex

Vortices are common phenomena in nature.Optical beam can carry orbital angular momentum,which is known as the optical vortex.Over the past three decades,optical vortex beam has unveiled a novel understanding of optics,leading to exploration of angu-lar momentum.Optical devices have been developed into integration and miniaturization,whereas it is hard to break the diffraction limit within traditional optical devices.Control-ling light at the nanoscale by exploiting ultra-confined polaritons–hybrid light and matter waves–in various materials empowers unique opportunities for many nanophotonic on-chip technologies,which can be categorized as surface plasmon polaritons（SPPs）,phonon polaritons（Ph Ps）and exciton polaritons（EPs）,etc.Akin to optical vortex beam in free space,surface polaritons can carry angular momentum as well.In this dissertation,gener-ation and manipulation of polaritons and plasmonic vortex are researched.Furthermore,by introducing the vortex beam as an incidence,Airy-like hyperbolic phonon polaritons are proposed.Finally,unidirectional exciton-polariton induced by spin orbit coupling effect is visualized in real space,and exciton polaritonic vortices are generated as well.Specifically,the content of the dissertation is enumerated as follows.First,as for SPPs,an optimized plasmonic vortex lens is designed to achieve sub-wavelength focusing and generate plasmonic vortex,the intensity of which is enhanced by at least one order of magnitude.Furthermore,three versatile plasmonic metasurfaces are proposed,one of which is designed to simultaneously manipulate far-and near-field orbital angular momentum.Traditional plasmonic vortex lens is usually designed for a monochromatic light.The second metasurface is proposed as a wavelength-dependent plasmonic vortex generator.And the third plasmonic metasurface is proposed to realize on-chip detection of spin and orbital angular momentum,which offers great potential in high-dimensional integrated photonic devices.Then,hyperbolic Ph Ps are studied.Mainstream approaches have relied interfacial techniques to control polaritonic wavefront so far,for example,refractive optics and moire engineering.Here,we propose that orbital angular momentum of incident light could of-fer a new degree of freedom to structure vd W polaritons.With optical vortex excitations,a new class of accelerating polariton waves–Airy-like hyperbolic Ph Ps in vd W crys-talα-Mo O₃is observed.Akin to Airy beams in free space,such Airy-like Ph Ps show self-accelerating,nonspreading and self-healing characteristics in propagation.Owing to the helical phase gradient introduced by incident vortex beam,the Airy-like Ph Ps pos-sess asymmetric propagation feature,analogous to hyperbolic shear polaritons in low-symmetry crystals.Finally,EPs in transition metal dichalcogenides are researched.By coupling spin photons into the tip of a scattering-type scanning near-field optical microscopy（s-SNOM）to mimic a circularly polarized dipole,we first report the real-space nanoimaging of unidi-rectional self-hybrizied EPs,where EPs with opposite helicities are transported to opposite directions（the ratio of unidirectionality is equal to 3.44）and the resolution can reaches to 10 nm.This work provides an alternative but more direct approach to uncover the underlying physics of optical spin-orbit coupling and EPs in vd W semiconductors.