The Holographic Plates With Blazed Grating Were Fabricated By A Femtosecond Laser To Realize Composite Vortex Beams

The discovery that optical vortices-light beams with a spiral phase singularity at center of helical wavefronts-carry orbital light angular momentum(OAM)has led to appreciable advances in optical microscopy,micromanipulation,photonic integrated circuits and quantum information and communication field.In addition,when a vortex beam is superimposed with another one,the phase distribution of the composite vortex is dependent on the composite vortex beams,and the superposed orbital angular momentum(OAM)states would also change due to the superposition of different vortex beams.Vortex beam generated by traditional methods,which optical purity may be lower,and the whole experimental system for large,complex.Here,we propose a kind of compact strategy to produce vortex beam with high purity,and optical superimposed vortex beams generated by designed structure.First,the concept of the vortex beam and the method of producing it are described systematically.Wave function and the characteristics of the vortex beam are introduced.Are introduced in detail,about the orbital angular momentum theory knowledge,including electromagnetic field carrying the orbital angular momentum.Then the most common and the latest detection of methods are introduced,such as spiral phase plate,spatial light modulator,q-plates,whispering gallery modes resonator,metasurfaces,etc.HPBG structure processing system,the process flow of femtosecond laser direct writing HPBG structure and diffraction efficiency and transmission efficiency of machining HPBG structure are introduced.Through detailed study on the diffraction efficiency and transmission efficiency,thus proving HPBG structure can produce efficient vortex beam.Through our own detection optical path,the detection HPBG structure pattern of the Fresnel diffraction light field can be observed in the intensity distribution and interference pattern of vortex beam.A single holographic plate with blazed grating(HPBG)can simultaneously generate and separate the first order optical vortices,and characterization of the phase singularities are proved in the overall.Finally,optical superimposed vortex beams generated by integrated holographic plates with blazed grating,which introduced in detail..We introduced the theoretical basis of superposed vortex beam.In order to superimposition the vortex light generated by a double HPBG structure,we further studied the relationship between the periods of blazed grating and the discrete angles of vortex beams.Through this relationship,we design the double HPBG structure,including the periods of blazed grating(4.06?m),radius(20?m),HPBG spacing between the structures(2?m)and the direction of rotation between HPBG structures.Through double HPBG structure of this design,two vortex beams can be superposed in a fixed space diffraction distance,without the background light.The superposed light field can be considered a kind of composite vortex light field,we further study the relationship between topological charges of the composite vortex beam and topological charge of a single vortex beams,and the corresponding relations of orbital angular momentum(OAM).And proved that our method is robust,it not only overcomes the traditional superposition of OAM need complex experimental system,and effectively produce the composite vortex light field with controllable topological charge.