Research On Key Technologies Of All-fiber Orbital Angular Momentum Mode Multiplexing Communications

The rapid development of modern science and technology enables the exponential growth of communication capacity.However,optical communication networks based on single-mode fibers(SMF)are gradually approaching their capacity limit.The development of the space physical dimension of light is expected to keep the communication capacity growing rapidly in the future.Among space physical dimension resources,orbital angular momentum(OAM)based mode-division multiplexing(MDM)is becoming a promising approach to increase the communication capacity because of the orthogonality of multiple OAM modes with different topological charge values.At present,the researches on OAM mode multiplexing are mainly in free space.In order to realize long-distance OAM multiplexing transmission,OAM based MDM in fiber is highly desired.The generation and multiplexing of OAM modes are the key technologies.In this thesis,the main work is to design an all-fiber mode-selective coupler(MSC)to generate and multiplex OAM modes.The all-fiber multiplexing transmission of two OAM modes is demonstrated in the experiment.In addition,we propose an eigenmode MDM scheme using an elliptical core fiber.The feasibility is proved by simulation results.The detailed research works are as follows.(1)The key technologies of OAM mode multiplexing and several fabrication techniques of MSC are briefly introduced.On the basis of the coupled-mode theory,the key parameters of the fused taper technique are achieved.We thoroughly study the fused taper technique,using which fiber-based OAM MSC is successfully fabricated.(2)The performance of the fiber-based OAM MSC is comprehensively characterized.Using the fabricated fiber-based OAM MSC,two OAM modes are successfully multiplexed and transmitted over a 2-km fiber.The performance of the all-fiber OAM MDM system is evaluated.(3)An elliptical core fiber supporting 6 eigenmodes as independent channels isdesigned.Meanwhile,a MSC for exciting and multiplexing eigenmodes is designed.A scheme of eigenmodes MDM system is proposed and its feasibility is proved by simulations.