| Traditional optical devices,such as prisms,lenses,and helical phase plates,rely on the phase accumulation of light during transmission to produce the desired wavefront.Generally,such optical devices have irregular geometric shape and large volume,which is not conducive to the miniaturization and integration of devices.Metasurfaces,a class of metamaterials with a reduced dimensionality,can introduce the interfacial phase discontinuity to realize the complete control of the phase,amplitude and polarization of the electromagnetic wave.Optical metasurface has the characteristics of ultra-thin and planar geometry,so that metasueface-based devices are easy to integrate with other optical devices to develop compact multifunctional optical devices.Discontinuous interfacial phase profiles introduced by metasurface can be spin-dependent phase,i.e.,the Pancharatnam-Berry phase,or spin-independent phase.The left-handed and right-handed circular polarizations incident on the Pancharatnam-Berry phase metasurface obtain the conjugate additional phase.Under the action of the conjugate additional phase,the incident left-handed and right-handed circularly polarized lights have different propagation behaviors.The reflection type metasurface based on metal resonator can ac hieve very high diffraction efficiency.Due to the ohmic loss of metal resonator,it is difficult for the transmission-type metasurface based on the metal resonator to obtain high transmission efficiency.All-dielectric metasurfaces can also introduce an abrupt interfacial phase discontinuity.Without metallic resonators,transmission-type all-dielectric metasurface can achieve very high transmission efficiency.Achieving high transmission efficiency is a critical step toward the practical application of devices.In this paper,we first study the modulation mechanism of Pancharatnam-Berry phase based on all dielectric metasurface,and then develop the spin-photonic devices based on all dielectric metasurface,such as spin-dependent splitters,longitudinal spin-dependent multifoci metalens,and photonic spin filters.The related work is as follows:1.The realization of photon spin-dependent splitting based on all-dielectric metasurfaces is proposed,and the intensity patterns of the split spots can be arbitrarily constructed.Previous work about photon spin splitter has been devoted to the splitting of two spin states,without further considering the spin dependent spot patterns after splitting.In practical applications,spin dependent spots with special intensity patterns are often required.Here,using the combination of spatial light modulator and all dielectric metasurface to realize the spin-dependent splitting with arbitrary intensity patterns.Firstly,the quantitative relationship between the separation distance of two circular polarization components and the one dimensional rotational rate of the optical axis in metasruface,and the transmission distance is theoretically calculated.Typical intensity distributions,such as vortex beams,Airy beams,Hermite-Gaussian beams,and special symbols are taken as examples to demonstrate the performance of the separated intensity patterns.The patterns of separated spots can be the same or inconsistent.Further experiments show that the separated spot presents two different intensity distributions.A high transmission efficiency and a high conversion efficiency enable the high quality of the separated spots patterns.The designed spin splitters can be used to analyze the spin state of incident light.The related results are expected to have some application s in information processing and spin encryption.2.Longitudinal spin-dependent multifoci metalens based on Pancharatnam-Berry phase metasurface is proposed.With the rapid increase of information and the higher requirement of communication speed,communication system becomes more and more complex.Therefore,it is urgent and important to develop compact and integrated photonic devices.Most components in optical communication system are made of glass.Therefore,directly integrating Pancharatnam-Berry phase elements into glass has great scientific value and application value.Here,the integration of Pancharatnam-Berry phase lenses and dynamic phase lenses is taken as examples to demonstrate integrating Pancharatnam-Berry phase elements into glass directly.The integrated lens forms on-axis spin dependent multifocal in the transmission edge of the metalens.Unlike the traditional lens,the intensity and spin state of the focus can be modulated by controlling the spin state of the incident beam.The integrated lens may have potential applications in 3D imaging,particle manipulation and optical communication systems.The method can be conveniently extended to optical fiber and laser cavity,which can be used to directly generate orbital angular momentum modes.It is expected to have potential applications in optical communication based on orbital angular momentum.3.A photonic spin filter based on two Pancharatnam-Berry metasurface is proposed.Photon spin offers a new degree of freedom for the control of light,and manipulation of the photon spin is the first step to use this new degree of freedom.A lot of work has been devoted to the manipulation of photon spin,such as photon spin Hall effect.However,the transverse shift of the two circularly polarized components created by the photon spin Hall effect is very small.To detect this small shift,quantum weak measurement techniques are often employed.Metamaterials provide an opportunity to enhance the separation distance of two circularly polarized components,but it is still a challenge to extract an expected spin component from the two separate spin components.Inspired by electron spin filter and spatial filter,a photon spin filter based on dielectric metasurface is proposed and demonstrated experimentally.The filter can effectively sort the expected spin state photons from the incident photons.The filter consists of two confocal Pancharatnam-Berry phase lenses and a diaphragm located at the common focus.The first Pancharatnam-Berry phase lens focuses the desired spin state photons,and diverges the other.Only the focused spin photons pass through the diaphragm.The second Pancharatnam-Berry phase lenses restore the propagation direction and spin state of photons to the case as if no spin filter is presented.4.A compact photonic spin filter is proposed,and the filter is used to extract the circularly polarized components of the vector beams on the higher order Poincaré sphere.The compact photonic spin filter is formed by integrating a Pancharatnam-Berry phase lens(focal length of ?f)into a conventional plano concave lens with focal length of-f.By choosing the incident port of the device,the compact photonic spin filter can select the photons with desired chirality to propagate alone its original propagation direction,while the photons with unwanted spin state is quickly diverged after passing through the photonic spin filter.The higher order Poincaré sphere can conveniently describe the vector vortex beam.The two poles of the higher order Poincaré sphere(two bases)represent the vortex beams whose chirality and topological charge are opposite,and the beams represented by the other points on the surface of sphere can be regarded as a coaxial superposition of beams on the two poles.The compact photonic spin filter can conveniently extract the two spin dependent components of the beam represented by any point on the higher order Poincare sphere.The designed photonic spin filter can conveniently extract the desired circular polarization component of arbitrary beams on the surface of the higher order Poincaré sphere.For simplicity and without loss of generality,five points on the longitude of azimuth angle(0?(28))on the higher order Poincaré sphere(l(28)2)are taken as an example.By comparing the theoretical results with the measured intensity distributions and the retrieved polarization states of the beams,it is found that the spin filter can effectively extract the desired circularly polarized components,such as right-handed or left-handed circularly polarized components.The compact photonic spin filter provides a simple method to manipulate light,and the principle may have potential applications in the design of photonic devices. |
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