Researches On The Technique Of Pulse Fiber Laser And Amplifier

High power, high energy pulse fiber lasers are considered as the prevalent tendency in the future by their many advantages. Now, the traditional pulse lasers have been began to be replaced by the fiber laser in some fields. Therefore, to research the pulse fiber laser is very meaningful and helpful for the development of the fields such as military, industry, and medicine. Firstly, the generation of pulse in the fiber laser is investigate. Then, the modulated semiconductor lasers as the seeders are researched in the experiment. On that basis, the MOPA technique is used, and the seed pulse is amplified to be a high power laser pulse by the fiber amplifier. Finally, the nonlinear effects which generate in the traveling fiber and fiber amplifier by high peak power pulse are researched in experiment systemically and analyzed with the corresponding theory.The main research works and innovations of this dissertation are summarized as follows:1. An all-fiber Q-switched Yb³⁺-doped fiber ring laser pumped with a 976nm laser diode (LD), which uses a fiber-pigtailed acousto-optic modulator as the active Q-switching element is reported. The stable pulse can be obtained when the modulation frequency is adjusted from 200Hz to 60.9kHz. The output wavelength of the laser is 1030nm. The maximum peak power is 2.7W, and the minimum pulsewidth is 53.2ns. A passively Q-switched Yb³⁺-doped double-clad fiber laser with homemade semiconductor saturable absorber mirror (SESAM) as the saturable absorber is demonstrated experimentally. The stable pulse of 29.4kHz repetition rate is achieved. The maximum pulse energy is 0.636μJ and the pulse duration is 3.148μs.2. The experiment of big signal modulated and gain switched semiconductor Laser are discussed. A distributed feedback semiconductor laser (DFBL) with linewidth of 1.64MHz and the wavelength of 1548nm is directly modulated to generate square-shaped optical pulses whose time duration can be varied in the range between 3.3ns and 200 ns, and the tunable repetition rate is 30kHz⁵0MHz. An external cavity FBG semiconductor Laser with wavelength of 1064nm and linewidth of 10MHz is used to the gain switched laser source. The pulsewidth of 186ps is achieved, and the tunable repetition rate range is 1kHz～120MHz.3. The multi-stage fiber amplifiers are used to amplified the seed pulse generating from the directly modulated DFBL by the MOPA technique. A maximum pulse energy of 25μJ with pulsewidth of 3.3ns is obtained at the wavelength of 1548nm by using a double-clad, single mode, Er:Yb co-doped fiber power amplifier.4. A novel technique to broaden and reshape the spectrum of picosecond laser pulse based on the seeder of gain switch laser diode and Yb³⁺-doped fiber amplification(YDFA) is reported. Using this method, a 7nm bandwidth seed pulse generated by a gain switch semiconductor laser diode is broaden to 20nm, and the rectangular-shaped, flat-top spectrum is achieved as well.5. A compact tunable high power picosecond MOPA source based on Yb³⁺ doped fiber amplifier of gain switch laser diode is demonstrated. The laser are composed of the first stage preamplifier, tunable filter, the second stage preamplifier, and two stages power amplifie. The preamplifiers use the single mode Yb³⁺ doped fiber to be the gain medium. The fiber coupled tunable filter is made by ourself and has adjustable linewidth. The large mode area Yb³⁺ doped double clad fiber and Yb³⁺-doped double clad photonic crystal fiber is used to the two power amplifiers respectively. The tunable pulses are further amplified to 6.8W average power with 80ps pulseswidth at 1 MHz repetition rate, and the center wavelength is tunable in the range from 1053nm to 1073nm with single mode beam quality. 6. The four kinds of nonlinear effects which are FWM, SPM, SRS and SBS are researched in experiment and discussed by the corresponding theory, which will be very helpful for the design of the fiber amplifier.