Research On Orbital Angular Momentum Mode Two-layer Erbium Doped Fiber Amplifier Based On Circular Photonic Crystal Fiber

Optical communication technology has been developed rapidly in the past decades.The optical fiber communication network based oin single?mode fiber(SMF)has spread all over the wor-ld.With a series of breakthiroughs of the various new technologies,the demand for data transmission is growing rapidly to improve people's life.Although mlultiplexing and higher or-der modulation technological breaktlhroughs have made the capacity of single fiber promoted to meet the increasing need,the transmission capacity is gradually reaching the capacity limit of the standard single-mode fiber.Space division multiplexing(SDM)system has great potential to solve this problem.It has strong compatibility with other fiber communication technologies.SDM increases the communication capacity of a single optical fiber by increasing channels irn spatial dimension.Our group has been studied photon orbital angular momentum(OAM)mode multiplexing technology,one of the SDM technologies.It has great potential to improve the communication transmission capacity.However,there are still many techniques needed to handle for implementation of long-haul MDM systems based oin OAM modes.OAM carrier signal amplification is one of those critical techniques.Erbium-doped fiber amplifier(EDFA)has made a great contribution to the development of optical communication.In this paper,EDFA which is suitable for OAM mode multiplexing technology is introduced.We propose and design a new EDFA with two-layer Erbium-doped based on the C-PCF.The performance of the OAM-EDFA with different parameters is analyzed to get an optimal design.The research are as follows:(1)The recent research of OAM mode multiplexing technology is studied and compared in this paper.The study of OAM technology is mainly based on the ring-core fibers(RCF)and circle photonic crystal fibers(C-PCF).In this paper,we choose the fiber of our design by analyzing and comparing the performance of different OAM fibers.The research of Erbium doped fiber amplifier for OAM mode(OAM-EDFA)based on different optical fiber structures is introduced in detail.The performance of different design is analyzed and the method is studied.(2)We presented a new design of OAM-EDFA with two-layer doped profile.The OAM-EDFA is based on the C-PCF which can stably maintain 18 eigenmodes(14 OAM modes).In our design there are more parameters than the one-layer doped structure,which means the flexibility of our design is higher.Parameters that affect the amplifier performance,such as the width of two doped regions,the doping concentrations,the length of the amplifier fiber,the pump power and signal power,are optimized by trade-off schemes.The OAM-EDFA can amplify 18 modes(14 OAM modes)simultaneously over the C-band with differential mode gain(DMG)lower than 0.1 dB,while keeping the modal gain over 23 dB and noise figure below 4 dB.