Study On Dissipative Soliton Fiber Laser

Fiber lasers have been extensively investigated for excellent gain property, highefficiency, low threshold, compact, economic, and stable performance. Thetraditional soliton formed by the the balance of Kerr nonlinliner effects andanormalous diserpison in a fiber laser with negative dispersion is stable and easy tobe achieved, however, its energy is limited to~0.1nJ according to the soliton areatheorem and the soliton will break up at a higher energy. The pulse energy of thestretched pulse can be one order of magnitude larger than the conventional solitonby controlling the nonlinearity through enlarging average intracavity pulse duration.A pulse with a parabolic shape can realize high energy since it can undergoself-similarly evolution in positive-dispersion region while maintaining its pulseshape. However, its energy is strictly limted by the finite gain bandwidth. Up todate, a novel kind of dissipative-soliton (DS) normal-dispersion fiber laser hasattracted great interest of researchers. The dynamic banlance between the gain andloss in the nonlinear system play an essential role in DS forming process. The DSsshow quite different physical characteristics from other conventional solitons. It canbreak through the energy limit of traditional solitons without wave breaking, so itcan find important practical and potential applications. In this dissertation, the DSpulse shaping mechanism and the pulse characteristics influenced by cavityparameters are investigated experimentally and theoretically based onnormal-dispersion fiber laser.The main contents of this dissertation are as follows:1. Stable DS modelocking is realized in a normal-dispersion erbium-dopped fiberlaser. The typical DS pulse (RS-DS) exhibits nearly rectangular spectral profileswith steep edges. Due to the positive dispersion and nonlinear effects, theRS-DS is highly chirped. It is found that the chirp is almost linear across thepulse, and the RS-DS can be compressed by single-mode-fiber to femtosecondlevel, near the transform limit. Besides, the pulse characteristics, the pulseshaping mechanism, and the evolution process are also analyzed numerically and theoretically, which is in good accordance with experimental results.2. Pulse evolution along with the variation of pump power is investigated. Thenumber of DSs increases (decreases) one by one with the ascending (descending)procedure of the pump power. Experimental results reveal that steady DSs arerestricted by an upper energy limit and affected by the energy quantisation effect,i.e., the necessary increment of pump power for generating one RS-DS pulseapproaches to a constant. The detailed DS pulse shaping process is alsoobserved experimentally, which also indicates that pulses with different energiescan coexist in the cavity. In addition, it is found that DS laser cavities can emitdifferent types of pulses at different pump powers.3. Traditional RS-DS pulses can not support higher energy since they will evolveinto multiple pulses at strong pump. Three different types of high-energywave-breaking-free pulses are observed in further experiment. For the first type,the pulse duration and bandwidth both enlarge with the increase of pump. Forthe second type, the pulse exhibit Gaussian shapes in spectral domain whilerectangular profiles in temporal domain. With the increase of pump, the pulseduration enlarges dramatically whereas the bandwidth and peak power keepalmost constant. For the third type, the bandwidth increases whereas the pulseduration decreases with the increase of pump At the maximum available pumppower, the fiber laser can deliver pulses with the bandwidth of~73nm, the pulseenergy of~200nJ, and the peak power of~3.5kW.4. Different types of pulses can also be achieved with different intracavitypolarization states. Four types of pulses (i.e., the RS-DS, the Gaussian-spectrumDS, the noise-like pulse, and the high-energy broadband pulse) with distinctcharacteristics are experimentally obtained in one fiber laser by adjustingpolarization states. Further investigation on pulse characteristics and formingmechanism is implemented by different means, such as launching the pulses intophotonic-crystal fiber for supercontinuum generation and orthogonal-polarization resolving the output pulses external to the cavity.