| As the next generation of ultrashort pulse laser light source,fiber lasers have numerous applications in optical communication,remote sensing,biomedical imaging,etc due to their distinct advantages of compact size,high efficiency and low maintenance cost.Meanwhile,the development and application of fiber lasers have been promoted by the rapid development of fiber manufacturing technology and various doping technologies,which can reduce the fiber loss and broaden the gain bandwidth of fibers,respectively.Especially,thulium-doped fiber lasers operating at ~2 μm have been intensively researched because of their important applications in scientific research,industry and military such as mid-infrared(mid-IR)frequency generation,laser processing,and pump sources for supercontinuum generation,etc.In recent years,the research on ultra-fast pulse thulium doped fiber laser at 2 μm band has made remarkable progress.Particularly,fiber lasers with high repetition rate and high pulse energy have always attracted significant research interests.In this thesis,based on the design of different specialty optical fibers,we numerically investigated two kind of specialty fiber lasers including high repetition rate fiber lasers and high pulse energy soliton fiber lasers.Through optimizing the parameters in the cavity,high repetition rate and high energy pulses are achieved,respectively.Main contents of this thesis are summarized as follows:(1)Research on high-repetition-rate fiber laser based on highly germania-doped fiber: Firstly,through optimizing the parameters of fiber,a highly nonlinear polarizationmaintaining fiber with group-velocity-matching between 2 μm and 1.55 μm is designed.The designed specialty optical fiber is employed to construct a nonlinear fiber loop mirror(NOLM)as an active mode-locker to offer intensity modulation to the laser cavity.Based on the cross-phase modulation of 1.55 μm pump light and 2 μm signal light in the cavity,an all optical actively mode-locked fiber laser is established.The Nonlinear Schrodinger equation is used to describe the pulses’ transmission in different optical components.Through optimizing the parameters in the cavity,a stable pulse with repetition rate up to 40 GHz is achieved.Moreover,the output pulse width and repetition rate can be flexibly adjusted by tuning the pump.(2)Research on high-repetition-rate soliton fiber laser based on tellurite photonic crystal fiber: In order to further improve the nonlinearity of the fiber and reduce the length of fiber required for cross-phase modulation,a tellurite photonic crystal fiber(PCF)which simultaneously offers the properties of higher nonlinearity and group-velocity matching between 1.55 μm and 2 μm band is designed.Based on this PCF,an actively mode-locked fiber laser is proposed to realize efficient all-optical injection modulation in the cavity.By means of numerical simulation,pulse width and repetition rate can be flexibly adjusted through tuning the pump accordingly.Moreover,a nearly transferlimited soliton pulse with repetition rate up to 40 GHz at 2 μm can be successfully obtained by optimizing the time bandwidth product of the output pulse.(3)Research on high-energy soliton fiber laser: In this paper,different mode-locked pulse based on different mechanism are analyzed firstly.And then a passively modelocked fiber laser with net normal dispersion is proposed based on the designed highly germania-doped fiber.The main parts of the laser contain the highly germania-doped fiber,a saturable absorber,an optical isolator,a 90:10 output coupler,a section of single mode fiber or thulium doped fiber and a Gaussian filter.Two kind of solitons including dissipative soliton and dissipative soliton resonance are realized by adjusting the cavity gain and loss,indicating pulse shaping in the cavity and high energy pulse output. |
