Study On Characteristics Of Orbital Angular Momentum Super-mode Microstructured Fiber

With the advent of the"Internet+"and the“5G”,the future internet must meet the needs of ultra-high speed data transmission.However,the current method of network expansion already has technical bottlenecks.So far,space division multiplexing has been proved to be an attractive method to break through the capacity limit of present optical communication system.For space division multiplexing,multiplexing of orbital angular momentum mode is considered as one of the most promising technologies.In order to transmit the orbital angular momentum in fiber,and combined with the advantages of flexible control of microstructured fibers,researchers have adopted ring-core microstructured fibers.However,to guarantee effective refractive index difference large between HE and EH modes which can forming the same order orbital amgular momentum,the ring-core has to be very narrow.Therefore,in this paper,a high refractive index column will be introduced into the ring-core.Based on the coupled mode theory,super-mode superposition is used to form the orbital angular momentum mode to achieve a large mode area.Firstly,the background and significance of microstructured fiber and orbital angular momentum is introduced in this paper.And this paper details the current research status of orbital angular momentum fiber at home and abroad.In addition,the transmission characteristics,formation methods and typical fiber of orbital angular momentum are also studied.Secondly,based on the coupled mode theory,this paper classifies the super-modes which formed by the fundamental mode coupling.The orbital angular momentum super-mode microstructured fiber is designed.Each high refractive index column is used as each core,and the modes in each core are coupled to form the super-mode.The effects of different parameters on the effective refractive index,refractive index difference,limiting loss,dispersion,and mode area of the fiber are studied.Finally,the optimal design scheme is proposed,and its mode area is increased by more than 6 times compared with the traditional ring-core fiber.Thirdly,the order of orbital angular momentum formed by the design scheme for the fundamental mode in single core is limited by the number of cores.This paper further extends the single core single mode to the single core multi-mode and the ultramultimode orbital angular momentum super-mode microstructured fiber has been designed.This paper introduces the tangential coupling and normal coupling of the HE_2,1 mode,proposes an fiber structure.The influence of structural parameters on fiber characteristics is studied.Finally,the optimal design scheme is given,which supports 56 modes of large mode area transmission.Finally,a kind of all solid orbital angular momentum super-mode microstructured fiber is designed.Compared with the air hole scheme,this structure is simple,the cost of design and preparation is low.Both sides of the all solid scheme ring-core are closed boundary conditions.In this paper,the refractive index of super-mode groups and cladding material are compared for different number of fiber cores.And reasonable parameters are selected to propose the optimal design scheme,the highest mode purity of the designed fiber exceeds 99.9%.