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Experimental And Theoretical Studies For Fiber Lasers Based On Erbium-doped Fiber And Fiber Raman Amplification

Posted on:2008-11-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:S QinFull Text:PDF
GTID:1118360212989564Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
With the development of the fiber communication technology and fiber-optical sensor technology, the optical devices which are compatible with optical fibers have been studied widely and in depth. Because of their advantages such as low cost, high reliability, flexible configuration and compatibility with fibers, and the potential applications in e.g. fiber communication systems, fiber sensors, optical spectrum analysis and RF generation, fiber lasers have attracted great interests. However, the intrinsic shortcomings in various current fiber lasers including multi-wavelength fiber lasers (MWFLs) such as power conversion efficiency gains, output stability and output spectral width, have influenced the performance and limited their applications.In this dissertation, we started with the studying of two different gain mechanisms used in fiber lasers — fiber Raman amplification and Erbium-doped fiber (EDF) amplification. By comparing the advantages and disadvantages between them, we focused the attention on MWFLs and proposed a novel hybrid gain mechanism which was used in MWFLs to suppress the intrinsic gain competition in Erbium-doped fiber amplifiers (EDFAs). Finally, a set of stable and uniform MWFLs in room temperature were obtained in our experiments.The theoretical analysis and numerical simulation on this hybrid gain mechanism were also proposed and the results showed that it can support stable operation of the fiber lasers.Another experiment was shown that this hybrid gain mechanism can also be applied in active mode-locked EDF lasers (AML-EDFLs) to suppress the supermode noise due to the gain competition in EDFA.This dissertation is organized as follows:In the introduction chapter, the history and present status of lasers and fiber lasers were introduced, and more attention was focused on the development process and current situation of MWFLs. In particular, the status of some key devices such as erbium-doped fibers, Raman fibers, pump sources and spectral filters were reviewed. The advantages and disadvantages of EDFAs, fiber Raman amplifiers (FRAs) and Semiconductor optical amplifiers (SOAs) were also introduced. At the end of this chapter, the main problems faced by MWFLs were presented.In chapter 2, the basic theory of EDFAs was studied, and the basic theoretical model was introduced and derived. Then, methods and processes of test and measurement on some important basic parameters of EDF were introduced. And then, an L-band EDFA with low noise and high gain was proposed and studied. Additionally, an ultra-broadband amplified spontaneous emission (ASE) source based on Bi-EDF was also studied and demonstrated.In chapter 3, characteristics of the medium gains and losses that impact the stability of multi-mode laser resonator, such as line broadening, gain saturation and mode competition were analyzed systemically. The rate equation of a multi-mode resonator was also studied.Then, taken the Sagnac loop filter as a main example, some key devices such as the resonators and spectral filters were analyzed theoretically and experimentally.In chapter 4, the stimulated Raman scattering (SRS) in fiber including some other nonlinear effects such as four-wave mixing (FWM) was studied theoretically. Then, the basic rate equations and coupled equations were derived from the semi-classical electromagnetic theory. And then, methods and processes of test and measurement on some important basic parameters for FRA were introduced. Finally, a Sagnac loop filter employed a section of photonic crystal fiber (PCF) was presented and a Raman MWFL was demonstrated in experiments.In chapter 5, the main tasks and major innovations of this dissertation were contained in this part. The different characteristics between EDF and fiber Raman gains were first compared experimentally, and then the hybrid gain mechanism based on EDFA and FRA was proposed. Furthermore, several MWFLs with various structures utilizing this hybrid gain mechanism were designed and studied. Since the gain of EDFA was much greater than the one of FRA, the hybrid gain mechanism can not be regarded as a simple combination of FRA and EDFA. With the experimental evidence on the absence of cross-saturation effects in fiber Raman, theoretical analysis and numerical simulation on the operation principle of this hybrid gain were proposed and the experimental results can be explained very well. Then, two novel methods of channel-spacing tunable and output wavelength range controllable MWFLs utilizing were proposed respectively.In chapter 6, the hybrid gain was used in AML-EDFLs, and the experimental results also show it can suppress the supermode noise in AML-EDFLs.In summary, this dissertation focused on the hot point of MWFLs, a novel method to obtain stable and uniform MWFLs in room temperature was proposed, and several important problems of MWFLs were studied theoretically and experimentally. Both theoretical and experimental results can play a role in guiding study on MWFLs.
Keywords/Search Tags:multi-wavelength, fiber laser, optical amplifier, Raman scattering, fiber Raman amplifier, Erbium-doped fiber amplifier, broadband source, gain competition, gain saturation, homogeneous broadening, inhomogeneous broadening
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