Design Of Microstructure Fibers And Analysis Of Rare Earth Doped Amplifiers

Microstructure fibers(MFs) have attracted much attention in the past twenty years, there are many special properties in MFs, such as endless single-mode, ultra large single mode core size, large mode area and controllable dispersion. MFs can avoid nonlinear optical effect, improve coupling efficiency of pump power and maintain low loss optical transmission in high pump and signal power. There are great potential applications in optics communication, high power optical transmission and high power amplifiers or lasers.The work in this dissertation is motivated by "Design of Ultra-large-core size single mode K9 photonic crystal fibers and analysis of K9-PCF amplifiers doped with rare earth ions" between University of Science and Technology of China and Xi'An Institute of Optics And Precision Mechanics Of CAS together with "Analysis of Segmented cladding fiber amplifiers" between University of Science and Technology of China and City University of Hong Kong. By analyzing the character of photonic crystal fibers and segmented cladding fibers, we design several ultra-large -core size single mode fibers with low loss, and analyze the rare earth doped MFs based on the model of rare earth doped MFs simulation and my own software about MFs amplifiers.The main research work and conclusions are as following:1. Based on the conventional rare earth doped fiber rate equations together with the normalized power density and population distribution, the rate equations of rare earth doped MFs are derived. Developing a software of rare earth doped MFs amplifiers, we provide a good simulation model of MFs amplifiers.2. We design a photonic crystal fiber at a core size of 20μm considering the advantage in processing and high doped concentration in K9 glass fibers, obtain its parameters such as: mode refracting index n_c(λ)=1.516, the single mode diameter D=21μm, mode area A_eff=345.8μm², and get its limit ellipticity ratio error is 94.7%, limit offset of inner hole is 0.1 um.3. We analyze a segmented cladding fiber, discuss its effective index distribution and dispersion curve, and obtain the parameters of a segmented cladding fiber with large single mode, small fundamental mode loss, large higher mode loss. Based on this fiber with Er³⁺ doped, we analyze in detail the amplification characteristics, and obtain its threshold pump power, pump power distribution and saturation output signal power. Finally we obtain its noise figure, and prove the rare earth doped segmented cladding fibers have many advantages comparing with conventional fiber, such as: the segmented cladding fiber has an mode area one hundred times larger than conventional fiber, its signal gain comparable with that of a conventional erbium-doped fiber, and its noise figure satisfy the requirement of fiber amplifiers.4. We analyze the amplification characteristics of Yb³⁺-doped segmented cladding fiber, and obtain its threshold pump power, pump power distribution, saturation output signal power and noise figure. By comparing the nonlinear power threshold in unit area with conventional Yb³⁺-doped fiber, we prove segmented cladding fiber can support high power. Finally, we discuss the potential applications in high power amplifiers and lasers.The innovative results in this dissertation are as following:1. By using the two-level and three-level propagation rate equations and power transmission equations in rare earth doped microstructure fiber, combing with Finite Element Method and Plane Wave Expansion Method, we design a software for rare earth doped microstructure fiber with large core size, which provide a good simulation tools for microstructure fiber amplifiers and lasers. We design a high concentration Er³⁺ doped photonic crystal fiber amplifier, whose single mode diameter is 21.6μm, the maximum gain can be 40 dB at a pump power of 500 mW.2. We design a microstructure fiber amplifier with Er³⁺ and Yb³⁺ doped, analyzing its amplification characteristics in detail, which has a dozens of times larger than conventional fiber, so can support much higher power. This microstructure fiber amplifier has a maximum gain of 37dB at several meters length, and its noise figure less than 4 dB. By nonlinear power threshold and damage threshold of fiber, we disscuss the application of microstructure fiber amplifier in coherent beam and the potential applications in rare earth doped high power fiber amplifiers and lasers.