The Study Of Cylindrical Vector Beams Transmission In The Ring-core Fibers

In recent years,with the emergence and the rapid development of new technology such as 5G mobile communications,high-definition video,cloud computing and Internet of things.Data center and metropolitan area network has faced enormous pressure of data capacity,which belongs to communications in short distance.The threshold of capacity in communication systems is rising,and the requirements for communication speed and quality are increasing at the same time.In order to increase the capacity of the existing single-mode optical fiber communication system,various multiplexing technologies by using different latitudes of light as channels have been proposed efficiently to meet future bandwidth requirements.However,the single-mode fiber as the single-channel communication system itself has the limit of Shannon.In order to meet the increasing bandwidth demand of fiber communication systems in the future,the new fiber multiplexing technologies and corresponding large-capacity transmission fibers are further explored to alleviate the data capacity crisis.The cylindrical vector beam(CVB)with a singularity of polarization is a kind of singular beam,and the intensity distribution is annular.Similar to the linearly polarized LP mode,CVB can also act as a carrier,providing a new multiplexing dimension for modular division multiplexing(MDM).The more the multiplexed CVB mode,the larger the system capacity is increased.The refractive index difference between the modes is inversely proportional to the crosstalk between the modes at the time of multiplexing.In order to take into account both transmission capacity and transmission stability,we need to select a ring-core fiber(RCF)with a high refractive index zone and CVB beams for transmission experiments.In order to match CVB and RCF efficiently,this paper proposes a beam shaping method for coupling.The main research contents and results of this thesis are as follows:(1)We demonstrate the shaping effect by using digital micromirror device(DMD)and spatial light modulator(SLM)on CVBs and then coupled CVBs into RCFs.Firstly,the eigenvector modes supported by three different RCFs are calculated by using the finite element calculation software COMSOL,and the effective refractive index corresponding to each mode is recorded.Then the CVBs are shaped by two kinds of modulators to form PCVBs of different order,and then PCVBs are coupled to different RCFs through the objective lens.Three RCFs with different structural parameters are completed,and we transmit CVBs with the lowest +2 order to the highest +7 order CVBs in RCFs during our experiment.(2)The optimization scheme for designing RCFs to transmit CVBs are given by calculation and simulation.Firstly,we use the finite element calculation software COMSOL to calculate the eigenvector mode of RCFs with different structural parameters.The effective refractive index values corresponding to each mode are also recorded.We analyze the maximum CVB modes order that RCFs can support under different conditions.And the number of CVB modes that can be supported in the case of satisfying the effective refractive index difference threshold are also analyzed.