Theoretical And Experimental Research On Wavelength-tunable Passively Mode-locked Fiber Lasers

The passively mode-locked fiber laser with central wavelength tunable can bewidely used in optical communication system. Hence, the passively mode-lockedfiber laser which pulse central wavelength can be tuned continuously is mainlystudied theoretically and experimentally in this thesis. In experiment, thedual-wavelength mode-locked pulses are obtained by semiconductor saturableabsorber mirror（SESAM） in linear cavity ytterbium-doped fiber laser. The passivelymode-locked pulse is realized by nonlinear polarization rotation（NPR） in ring cavitydouble-clad erbium/ytterbium co-doped fiber laser. The detail research work can beclassified as follows:1. Wavelength-tunable SESAM mode-locked linear cavity ytterbium-dopedfiber laser. The passively mode-locked pulse with the repetition rate of16.42MHz is achieved, which maximum average output power is10.2mW andsingle pulse energy is0.63nJ at central wavelength of1030nm. Volume Bragggrating（VBG） acts not only as the mirror of the laser cavity, but also thewavelength tuning device. By adjusting VBG, the central wavelength of themode-locked pulse is tuned from1011.9nm to1050.6nm qualitatively andquantitatively, which tuning range of38.7nm. Based on the grating formula,every output wavelength matches one of the angles of VBG. Through adjustingthe VBG along clockwise, the pulse wavelength is tuned to longer wavelength;conversely, it becomes shorter.2. Wavelength tunable dual-wavelength linear-cavity passively mode-lockedYtterbium-doped fiber laser based on SESAM. This fiber laser is constructedwith an Yb-doped fiber and two branch cavities by polarization-maintaining beamsplitter. This laser system can output simultaneous dual-wavelength pulses withthe qualitative and quantitative wavelength tuning range of1020.3~1038.5nm and1027.2~1055.1nm by net gain equalization method at room temperature with themaximum and minimum wavelength separation of34.8and2.4nm, whichrepetition rate of11.39and11.41MHz respectively. And their maximum singlepulse energy are0.47and0.33nJ.3. The mode-locked ring cavity double-clad erbium/ytterbium co-doped fiberlaser based on nonlinear polarization rotation. The passively mode-locked pulse is obtained with the repetition rate of12.12MHz, which optical spectrum bandwidthis5.26nm and signal-to-noise ratio is60dB at the central wavelength of1568.98nm. The minimum pulse duration is1.78ps. The central wavelength ofthe mode-locked pulse is tuned from1564.60nm to1568.98nm by adjustingpolarization controller with the tuning range of4.38nm. The maximum averageoutput power is52.2mW at the pump power of3.9W.4. Self-Q-switched and self-mode-locked ring cavity double-claderbium/ytterbium co-doped fiber laser. When increasing the pump powergradually, the repetition rate of the Self-Q-switched pulse is tuned from4.17KHzto55.56KHz. At the same time, the pulse duration is tuned from11.9μs to8.1μs.The repetition rate of the self-mode-locked pulse is12.58MHz with the opticalspectrum bandwidth of3.15nm at1565.80nm. The self-mode-locked pulsedisappears when the pump power is higher than2700mW.