Research Of The Generation And Detection About Vortex Beams

In 1992,Allen et al.recognized that beams with an azimuthal phase dependence of exp(7)il?(8)carry the orbital angular momentum(OAM).Where ? is the angular coordinate and l is the topological charges.Such beams have helical wavefronts and they are usually called “vortex beams”.The vortex beam carries OAM of quantity of lη per photon.Compare with the Gaussian beam,the vortex beam has extra dimension emerging from the spatial distribution.So,the vortex beam has numerous applications in free-space optical communication,optical microscopy,quantum coding,optical tweezers,manipulation of Bose-Einstein condensates etc.In recent years,with the developing of related research fields on vector beam theories,vector beam has also a doughnut-shaped intensity pattern,and the intensity on the beam’s center is zero.It’s difference about the Laguerre-Gaussian beams which have the uniform electric field distribution and independent spiral phase.This is because vector beam’s electric field may have a in-homogeneous direction caused by the in-homogeneous phase distribution across the beam.In this work,the methods of generating helical beams and observing the orbital angular momentum were demonstrated.The research contents include:(1)Summarizing the theories about LG beams and vector beams,and proposing the theoretical basis for OAM beams’ generation and detection.(2)Analyzing the theories about the diffraction grating to generate and measure the vortex beams,and facilitating the subsequent analysis of vortex optical field distribution.(3)Analyzing and simulating the method of segmented wave plates to generate the vortex beams,designing a new type of composite wave-plate,which can produce more of the higher-order modes of OAM beams.Designing novel hollow trustum of a pyramid to generate vortex light based on the total internal reflection.(4)Proposing the method of using the combination wave-plates to detect the OAM of vortex beams,and designing a detection device which can measure any OAM modes of vortex beams.The results show that: taping together several the same small segmented wave plates with different discrete crystal angles can get many high-order modes of vortexbeams;The hollow trustum of a pyramid can convert a polarization light to another polarization light with OAM based on the theory of total internal reflection,which has similar character of the segmented wave plates;The composite wave-plate can be used to detect the OAM light.In addition,we design a system to measure arbitrary vortex beams with difference topology numbers.