Design And Performance Analysis Of A Novel Photonic Crystal Fiber For OAM Mode Transmission

With the rapid development of the information,the demand for communication capacity has been increased exponentially.People have put forward higher requirements for data transmission capacity.In order to solve the crisis of communication capacity,new technologies are constantly emerging.Because there is an orthogonal relation between the OAM modes with different topological charges in space,and its topological charges are theoretically infinite.Orbital Angular Momentum?OAM?optical communication provides a potential solution for the lack of communication capacity.Using OAM beams as the information carrier of the communication system has attracted wide attention.The transmission medium is the key device in OAM optical communication.At present,there are two kinds of OAM transmission medium,free space and optical fiber.In free space optical communication,the current transmission rate can reach Tbit/s,and the number of OAM modes can reach dozens.However,the transmission of OAM beam in free space is easily impacted by atmospheric and external environment changes.The transmission distance is short and the energy distribution is divergent.So the transmission of OAM in optical fiber is currently a hot research topic.In this paper,the theoretical basis of OAM transmission in optical fiber is analyzed,and a new type of OAM photonic crystal fiber is designed.In this photonic crystal fiber,the air holes in the inner layer of the cladding are designed as square air holes.Using the COMSOL Multiphysics software based on FEM,we simulate and analyze the influence of the various structure parameters of the fiber,including the influence of the radius of core and the distance from the center of the fiber core to the cladding on the fiber dispersion,nonlinear co_efficient etc.The minimum dispersion is 52ps/mode ps/?nm·km?,and the nonlinear co_efficient is 1.41km^-1·w^-1).The simulation results show that the OAM optical fiber can transmit 54 mode.And the difference of _effective refractive index can reach 3.45×10^-3,_effectively reducing the degenerate between vector modulus.What's more,the structure of the photonic fiber can be designed flexibly.Compared with the existing OAM optical fiber,the number and mode characteristics of OAM mode transmitted in the new photonic fiber have been improved,which has great potential in improving transmission capacity.