Study On Vortex Fiber Amplifier

In recent years,the demand for optical fiber communication capacity has been increasing,while the transmission capacity of traditional standard single mode fiber is gradually approaching the theoretical limit.Therefore,there is an urgent need for new multiplexing technology to increase the communication capacity.The orbital angular momentum(OAM)multiplexing technology is a new form of spatial division multiplexing.As a multiplexing mechanism,utilizing the orthogonality of the OAM mode can break the Shannon capacity limit of single-mode fiber and greatly increase the transmission capacity.In order to realize the long-distance optical fiber transmission of OAM modes,the high performance vortex fiber amplifier is indispensable.Reducing the difference of modal gain to achieve gain equalization of all mode channels is an important criterion when designing optical fiber amplifier.Based on the theoretical model of erbium-doped vortex fiber amplifier,this paper studies the gain characteristics of optical amplifier based on vortex fiber,and mainly analyzes the gain equalization characteristics of fiber amplifier.Considering the actual process,this paper firstly optimizes the distribution of erbium ions based on a ring-core vortex fiber structure,and a partially erbium-doped fiber structure is proposed.We analyze the mode gain characteristics of the structure in detail.The results show that this structure can achieve the gain equalization of 6 OAM modes with the differential modal gain(DMG)less than 0.18dB and the minimum gain larger than 21dB.In order to achieve more amplification of the OAM modes,this paper further analyzes the amplification characteristics of an air-core vortex fiber structure which can support 12 OAM modes.By adjusting the pump mode and optimizing the distribution of erbium ions in fiber,we realize gain equalization of 12 OAM modes.Numerical simulation results show that the proposed stepped erbium-doped structure can provide DMG less than 0.26dB,with the minimum gain larger than 21 dB.Our work has guiding significance in the design and manufacture of vortex fiber amplifiers.The designed erbium-doped vortex fiber amplifiers have certain application value in the field of OAM modes multiplexing technology.