Experimental Studies, Analysis And Design For Erbium Doped Fiber Amplifiers With Low Noise Figure, High And Flat Gain

Erbium doped fiber amplifier (EDFA) is a key part in an optical fiber communication system. Combined with the dense wavelength division multiplexing (DWDM) technology, optical fiber amplifier is the current trend of optical fiber communication. With the rapid growth of all-optical and high-speed networks, the gain bandwidth of a conventional C-band EDFA cannot satisfy the requirement of a DWDM system. Furthermore, the gain of each channel will change dynamically with the network reconfiguration for a uniformly broadened EDFA, which will finally influence the stability of the communication system. It is thus of importance to develop an L-band EDFA. However, a conventional L-band EDFA is relatively inefficient and has low gain and high noise figure since they are operated at the tail of the erbium gain band. Therefore, it is very important to design and analyze a high performance L-band EDFA with simultaneously high gain, low noise and low gain ripple for a DWDM system.With the support of a major research grant of Zhejiang Province (No. 001101027) and the Plan of Promoting Education of Excellence of Zhejiang University in the 21st Century, this dissertation is devoted to address the above problems and fabricate an L-band EDFA with low cost, high performance and technological innovation.First the mechanism of an erbium doped fiber amplifier is introduced. Various theoretical models based on classical rate propagation equations are summarized and compared for their applications. We use a modified numerical model based on the Giles model, which agrees with the experimental results well. This serves as the theoretical base for the whole thesis and will be used to optimize the characteristics of EDFAs. A novel method based on a map of noise figure and gain is proposed to analyze efficiently the dependence of the noise figure and gain for EDFAs on the EDF length and the pump power. The characteristics of various EDFAs are studied and compared.Secondly, some important parameters are introduced to describe the characteristics of EDFAs. The methods and the experimental setups for measuring the gain and noise figure of an EDFA are emphasized. We introduce how to measure the characteristics of each component of an EDFA, especially the gain and absorption coefficient of an erbium doped fiber (EDF).Thirdly, four types of simple and novel L-band EDFA structures with low noise, high gain and low gain ripple are proposed to satisfy the requirement of a DWDM system. They can be classified into two categories. In the first category, a single ASE pumping is served asa secondary pump. This category includes the following three types. Type (a): a new construction using a fiber Bragg grating (FBG) in an unpumped EDF section at the input side. Type (b): a new structure of L-Band EDFA with two-stage pumps, which utilizes the forward ASE as a second pump. Type (c): a new two-stage, pump-allocated L-band EDFA structure with a single fiber grating. The second category is to use double ASE pumps. For example, Type (d): a novel three-stage L-band EDFA with very large and flat gam and very low noise presented in this thesis. It uses the forward ASE from the first section of the EDF and the backward ASE from the third section of the EDF (both serve as the secondary pump) to pump the second EDF. Note that all these structures are numerically simulated firstly and then verified by the experiments.Fourthly, in accordance with the need of gain control in a wavelength division multiplexed system, a gain-clamped L-band EDFA using a single fiber Bragg grating (FBG) is proposed. Based on the Giles Model with ASE, numerical simulation for the all-optical gain-clamped EDFA is carried out. The influence of the configuration, the pump wavelength, the Bragg wavelength, the reflectivity, the pump power and the length of EDF to the gain-clamped characteristics is studied. An optimal L-band gain-clamped EDFA configuration with appropriate parameters of the amplifier, which can also provide a flat-gain band, are given.Finally, the mechan...