Research On Vortex Beam Detection Technology Based On Spindecoupled Metasurface

To promote the transmission speed of the communication system,both SAMs and OAMs of light have been utilized to expand the dimensions of quantum information,optical communications,and signal processing,wherein unambiguous SAM and OAM identification is of great research significance.Most of traditional OAM detection approaches require complicated optical setups or bulky devices,which is in inconformity to the development trend of devices that pursue miniaturization and integration.Problems still exist and OAM mode recognition still faces many challenges.Emerging as a universal wavefront shaping platform,metasurfaces have the advantages of ultra-light,ultra-thin,and highly integrated,which provide opportunities for solving the above-mentioned problems.The current metasurface detection vortex beam device can only detect no more than 10 OAM modes,with a single function under a specific working wavelength.To solve those problems,geometric phase type and composite phase type metasurface devices are designed to realize multifunctional vortex beam detection.The main content of this paper includes:1.A broadband metasurface device based on the azimuthal-quadratic phase of photon momentum transformation(PMT)is designed to realize the detection of left vortex.A novel optical transformation mechanism is proposed for OAM modes identification,which transforms the azimuthal-linear phase of vortex beams into azimuthal rotation of focusing patterns in the far-field focal plane,and then the azimuth of the focal point is measured to realize OAM mode recognition.The numerical simulation shows that any OAM mode with up to ±100 order can be measured,and the OAM beam with 41 superposition modes can be measured simultaneously with a step size of 5.Experiments have measured the results at 480 nm,532nm,580 nm and 633 nm wavelengths,which prove that the designed PMT metasurface has the ability to recognize broadband OAM simultaneously.These results opened up a new way for future compact OAM communication systems.2.A composite phase metasurface device combining transmission phase and geometric phase is designed,and the simultaneous recognition of SAMs and OAMs is realized through asymmetric photon spin.Vortex beams of different spins are transformed into focusing patterns on two separated halves of the screen on a transverse focal plane with topological charge-dependent azimuthal rotations.PMT metasurface was experimentally demonstrated at several different wavelengths in the visible band.Further experimental investigations have proven that the single spin-decoupled metasurface possesses the ability to detect cylindrical vortex vector beams(CVVB)with simultaneous phase and polarization singularities.Finally,we showed that the proposed approach could be extended to sorting of superimposed OAMs with a proper mode interval.These results reported here may have many important applications in momentum measurement of both the spin and angular momentum and singularity detection of both phase and polarization singularities.