Research On All-fiber Q-switched Pulsed Fiber Laser

In recent years, with the advantages of good beam quality, high energy and peakpower, the Q-switched pulse fiber laser has attracted widespread attention in manyfields, such as industry, communication, medicine, military and so on. Especially inthe field of industrial processes, shows its unique advantages in green machining. Atpresent, the research on Q-switched fiber laser mainly focus on the realizaton of highpower and energy of the pulse at home and abroad, lack of detailed analysis of thedynamic characteristics of the pulse and the research of pulse control. Therefore, thispaper researches on all-fiber Q-switched pulsed fiber laser from two aspects of thedynamic output characteristics and the pulse control deeply, the following work hasbeen done:Firstly, we summarized the theory of Q-switched fiber laser, and introduced theworking principle of self-Q-switched fiber laser and acousto-optic Q-switched fiberlaser respectively. The working characteristics of Q-switched fiber laser wereintroduced from rate equations, peak power, pulse energy and pulse width. Theimplementation methods of Q-switched fiber laser were summarized and compared.Secondly, on the base of self-Q-switched fiber laser, we designed and built aself-Q-switched erbium-doped fiber laser based on a saturable absorber. The dynamiccharacteristics of the laser were analysised from two cavity shapes of linear cavity andring cavity separately. The linear cavity structure laser output experienced runningstate from continuous wave to the self-Q-switched pulse. In a pump power range from21mW to190mW, the self-Q-switched pulses can be obtained with the pulse widthtunes from8μs to100μs and the repetition rate tunes from2.5kHz to54kHz. Thejitter of repetition frequency and peak power is less than10%and5%respectively.The ring cavity structure laser output experienced running state from theself-Q-switched pulse to continuous wave. In a pump power range from16.2mW to110mW, the self-Q-switched pulses can be obtained with the pulse width tunes from138μs to180μs and the repetition rate tunes from2.8kHz to3.4kHz. The jitter ofrepetition frequency and peak power is less than5%and11%respectively. Wecompared and analyzed the dynamic output characteristics of two different cavitystructures. The research results are helpful to study the stability problem ofQ-switched pulsed fiber laser further and improve its practicability. Then, since the self-Q-switched erbium-doped fiber laser has limitations in termsof pulse control, in order to study the pulse chontrol problem, we designed and builtacousto-optic Q-switched fiber laser systems from two different pump structures offorward pump and backward pump separately. In the two laser systems with differentpump structures, we obtained the minimum pulse width of pulse was24ns and19nsrespectively, the repetition rate was80kHz. We compared the performance of the lasersystems with two different pump structures from the aspects of average power, pulsewidth, pulse smoothness and stability, the results showed that the backward pumpstructure is better than the forward pump structure.At last, the pulse control methods of acousto-optic Q-switched fiber laser wereresearched based on the backward pump structure. We studied the effects of the signalrepetition frequency and duty ratio on the pulse average power, pulse width andrepetition frequency, and given the theoretical explanations respectively. Finally, thepulse repetition frequency and pulse width can be controlled individually by anexternal control signal, we obtained stable and smooth pulse with the repetition ratetuned from10kHz to100kHz and the pulse width less than100ns.In addition, the change of repetition frequency with duty ratio in experimentswere analysised in detail. We explained the phenomenon from the relationshipbetween the opening time and pulse build-up time of the acousto-optic modulator, andwe found it was related to the smoothness control of pulse, this is a new idea in theresearch of the pulse control,This paper researched the dynamic characteristics and the pulse control problemsof the all-fiber Q-switched pulsed fiber laser by passively and actively Q-switching.Finally, the parameters of laser such as the stability, smoothness, repetition frequencyand pulse width can be flexible controlled, we obtained the smooth and stable pulsewith narrow pulse width. This laser is suitable for a high quality seed source in themaster oscillator power amplifier(MOPA) system, it helps to improve the machiningefficiency and quality in industrial processing, and has good application value.