Study On Gain And Noise Characteristics Of Few-mode Fiber Amplifier

With the emergence of new services such as Internet and Internet of Things,people put forward higher requirements for communication capacity.Space division multiplexing,including core division multiplexing and mode division multiplexing,is one of the key technologies to improve channel capacity.Mode division multiplexing uses mutually orthogonal modes as independent channels for information transmission,so that the communication capacity of optical fiber system can be greatly improved.In order to realize the long-distance transmission of the modes,high performance Fiber Amplifier is necessary.Erbium Doped Fiber Amplifier(EDFA)is used to amplify the C-band signal,which is of great significance for the development of optical Fiber communication.In this paper,the gain and noise characteristics of few-mode Erbium Doped Fiber Amplifiers(FM-EDFA)are studied.The main contents are as follows:(1)Based on the rate equation,the theoretical model of EDFA based on scalar mode is given,and the performance index and numerical solution algorithm of EDFA are introduced.(2)Two kinds of erbium-doped fiber with few mode are designed.The fiber structure is step type and ring core type,respectively.The gain equalization of the signal is realized by optimizing the erbium-doped concentration,erbium-doped range,pumping power,signal power and fiber length,and the gain competition of multi-mode signals and multiwavelength signals in the transmission process are analyzed.The results show that the fiber length is a key parameter to achieve signal gain equalization when signals of different wavelengths and modes are transmitted simultaneously in the fiber.By optimizing fiber length and sacrificing part of signal gain,gain equalization of multiwavelength and multi-mode signals is realized.(3)The noise characteristics of erbium-doped fiber amplifier(EDFA)are analyzed by full bandwidth noise model and equivalent bandwidth noise model respectively.For the equivalent bandwidth noise model,when the central wavelength is fixed,the change of noise power with different equivalent bandwidths and the influence on the signal gain(G),differential modal gain(DMG)and Noise Figure(NF)are analyzed.The results show that the noise power is proportional to the equivalent bandwidth,and the larger the equivalent bandwidth,the lower the signal gain,and different equivalent bandwidths have different effects on the signal gain equalization.For the full bandwidth noise model,the influence of noise model on G,DMG and NF is analyzed when the bandwidth range is determined.By comparing the results of the equivalent bandwidth noise model with the full bandwidth noise model,it is concluded that the gain and noise characteristics of the system can be accurately analyzed by using an equivalent bandwidth noise model which is close to the actual noise.In this paper,the gain and noise characteristics of the few-mode fiber amplifier are studied.The conclusion of this paper is of guiding significance for the study of the gain and noise characteristics of the few-mode erbium-doped fiber amplifier.