Research On Ytterbium-doped Fiber Continuous Laser And Mode-locked Laser

Fiber lasers have good beam quality,wide wavelength range and high conversion efficiency.Furthermore,because of compact structure and stability,fiber lasers will not be easily affected by the external environment.Due to these advantages,fiber lasers have been widely concerned and vigorously developed.On the other hand,ytterbium ion has a wide range of applications due to its simple energy level and high quantum efficiency.Therefore,this paper takes ytterbium-doped fiber laser as the research topic.Specifically,the linear polarized single longitudinal mode ytterbium-doped fiber continuous laser and low repetition frequency ytterbium-doped fiber mode-locked pulse laser are investigated and experimented.The contents are as follows:Firstly,a pair of fiber Bragg gratings is used to construct a linear cavity to achieve continuous laser output.The output of linearly polarized laser with the degree of polarization higher than 35 dB is achieved by inserting a polarization splitter into a linear cavity.In addition,a saturated absorber structure composed of un-pumped fiber and reflector is used to achieve single longitudinal mode laser output.The maximum power of direct output of seed source is 212 mW,the optical signal-to-noise ratio is 50 dB.Secondly,the laser output of 1064 nm with 2.552W can be obtained directly by using the double-clad ytterbium doped fiber for primary optical amplification without pre-amplification because the output power of the seed source is high enough.Moreover,the amplified laser still maintains the characteristics of high linear polarization(degree of polarization above 35 dB)and operates stably at single longitudinal mode state.The laser linewidth is 1.2 kHz measured by using delayed self-homodyne method.The mode-locked laser oscillator is realized by using a linear cavity constructed by a semiconductor saturated absorber mirror and a fiber Bragg grating.The laser at 1063.67 nm with pulse repetition frequency of 18.30 MHz and average output power of 1.52 mW has been achieved.The laser was pre-amplified to obtain a pulsed laser with the average power of 66.5 mW.Then,an acousto-optic separator and an acousto-optic modulator are used to reduce the repetition frequency.Finally,a picosecond pulse output with a repetition frequency of 18.30 kHz and a pulse width of 3.523 ps is obtained.