Vortex Beam Generation Using Spiral Holograms

Vortex beam is a type of special beam with orbital angular momentum in the course of propagation.The beam possesses phase factorexp(7)il?(8),of which l represents its topological charge.The particularity of vortex beam is that the orbital angular momentum of every photon is,which makes it have wide application prospects in many fields,such as microscopy,nanometer manipulation,astronomy,crystallography and so on.In addition to the possession of orbital angular momentum,and vortex beams with different azimuth angles of coaxial transmission are orthogonal to each other.The fact enables it to have great potential in free space communication and quantum communication of multiplex transmission.A great deal of research on vortex beam is aimed at how to transform the ordinary plane wave into the needed vortex beam.For example,the plane wave can be transformed into vortex beam directly by the spiral phase plate.This method looks simple,but the demand of process precision is very high,especially for high order vortex beams.The vortex beam can be easily generated by using a fork shaped hologram.However,this method will produce a lot of vortex beams with different topological charges,and the overlap between the high-order vortex beams will occur.At present,the spiral holography is a research hotspot,because in this way vortex beam of single mode with high quality can be produced,but the focusing effect of the vortex beam produced by this means will come up in the process of transmission.In the thesis,a new method for generating vortex beams is put forward.On the basis of the method of spiral holography,the spiral holographic screen is replaced with the Archimedes spiral diffraction screen.The vortex beam can be got by using the plane wave to irradiate the diffraction screen,and the generated vortex beam will not focus in the transmission process.This method develops a new way for the generation of vortex beams.It provides a new perspective for the existence of vortex beam in nature.The contents of this thesis are as follows:1.The background and purpose of the subject research is introduced.In this thesis,the research history of vortex beam and the research trends at home and abroad are introduced in detail.The application of vortex beam in the manipulation of micro-nano particles and optical communication is introduced.2.A general overview of vortex beams is presented.The related theory of vortex beams is introduced in detail.Several common methods of producing vortex beams are described.3.A new method for generating vortex beams is put forward.The theoretical model of this method is introduced in detail.The light intensity distribution and phase distribution of the beam are got by Matlab simulation.It is proved that what is produced by this method is the vortex beam.And it is proved that the vortex beam produced by this means will not focus.4.On the basis of the previous diffraction screen,two new diffraction screens are presented.It is proved that the two kinds of diffraction screens can also produce vortex beams.In addition,a new method is proposed for the superposition interference of vortex beams with the topological charges of equivalent magnitude and opposite symbol.