Generation And Manipulation Of Structured Light By Dielectric Metasurfaces

The customization of intensity,direction of wavevector,phase,and polarization of light endowed a great flexibility in the research of light fields and the development of new light applications.In traditional optics,the uniform and homogeneously polarized light produced by lasers provided a well light source in light detection,communication,and mechanical processing,which is widely used in industry and daily life.However,with the development of technologies for generating and modulating,variety of structured light field is getting more and more attentions recently.These sculpted lights break the limitations met in general optical fields in all degree of freedoms,and makes the new application of light be more accessible.Vortex beam is a prominent representation of structured light,which ca n theoretically provide infinite orbital angular momentum carriers for data coding and transmitting.Vector beam is another kind of structured light with inhomogeneous polarization states.As its vector properties,new diffraction algorithm is required in this realm.Applications in light-matter interaction,high resolution imaging,and quantum computing are expected to be found in the research of these vector lights.In this paper,dielectric metasurfaces are applied to generate and tailor the structured l ights.By shaping the subwavelength structures contained in metasurfaces,we can intentionally modulate the local polarization states of light.Also,with the evolution of polarization states,the related geometric phases can be used to modulate the phase structure.This method presented a versatile solution to produce all kinds of structured fields and can be superposed and miniaturized to realize the optical integration.The paper includes the following four major parts:1.A spin dependent splitting can be found in some situations in generating structured lights.This effect is a representation of light-matter interaction and will destabilize the light field.We experimentally verified that the spin dependent splitting can only be observed in the structures without rotational symmetry.When light passes through a fan-shape metasurface,a spin dependent splitting can be observed and will increase with the propagation.After enough accumulation,we observe a spatial shift in the optical far field.This research verified that breaking rotational symmetry is the prerequisite to observe the spin dependent splitting,which is meaningful for producing stable light.2.The spin dependent splitting leaded by breaking the rotational symmetry of structure is closely related to the photonic spin-orbit interaction and spin Hall effects.We extrapolated the rotational Doppler effect from time coordinate to position coordinate,thus found a feasible approach to manipulate the spin dependen t splitting.By changing the spatial rotational rate of structure patterns,a transverse component of wavevector will be added to shift the scale and direction of splitting.This work uncovered the relationship in polarization evolution,variation of wavev ector,and geometric phase,and gives a solution to modulate the topological charge of vortex beams.3.Cylindrical vector beam is the light beams with cylindrical symmetric polarization distribution,which is the vectorial solution of Maxwell equations.Plenty of applications in micro-and nanoparticle manipulation,photonic computing,and super-resolution imaging requires a convenient generator to obtain arbitrary cylindrical vector beam.However,traditional approaches can usually produce only one particular vector beam,and the setup also seems to be cumbersome.Based on the high transmitted dielectric metasurfaces,we present a simple and convenient method to yield arbitrary cylindrical vector beams and realize its evolution on high-order Poincaré sphere.Our method may provide a convenient and versatile way to generate the cylindrical vector beams,which is expected to provide a platform for studying the topological properties of vector lights.4.Perfect vortex beams are the orbital angular momentum(OAM)carrying beams with fixed annular intensities under varying propagation distance,which provides a better carrier of OAM than traditional Laguerre-Gaussian beams.Perfect vector beams can also overcome the influence induced in propagation,that is an ideal source of vector beam.However,ordinary schemes to obtain the perfect vortex beams are usually bulky,unstable,and cannot be miniaturized,which is therefore restricted in integrate optics.We demonstrate here a novel generation scheme to generate perfect vortex beams and perfect vector beam based on dielectric metasurfaces.It is predictable that the stable and integratable perfect vortex beam and vector beam generator will be indispensable in the future of optical applications.