Analysis Of Fiber Lasers With C+L Broadband Spectrum And High-repetition Square-wave Pulse

Since fiber lasers possess characteristics of excellent compatibility, good optical quality, high energy efficiency, low cost, compact structure and wide tuning range, they can meet the needs of kinds of fields, such as communication, medicine, industry and so on. Therefore, the study to optimize the performance parameters and analyze output characteristics of fiber lasers is of great importance. In this thesis, the analysis and applications of C+L band spectrum、high-repetition square-wave pulse is the major works. The major works about fiber laser with C+L band spectrum and high-repetition square-wave pulse are as follows:1. The3dB bandwidth spectrum of58.5nm and20dB of300nm have been achieved in a NPR laser cavity in anomalous dispersion by means of dispersion management experimentally. While the pulse width is28.89ps, which means giant chirp. In the same structure in normal dispersion, by taking advantages of the gain of C-band and L-band Erbium fiber, the spectrum has been generated with3dB width of60nm and20dB spectrum covers the whole C+L band;2. Square-wave pulses with repetition of8.54MHz have been generated in a NPR passively mode-locked fiber laser. The pulse width can be tunable from881.4ps to6.65ns and the ultra-broadband spectrum is88nm.3. Then stable square-wave pulses with repetition of7.05MHz have been generated in a28.38m fiber resonant cavity with normal dispersion. Besides, the phenomenon of dissipative soliton resonance has been successfully observed. The width of the square-wave pulse increases linearly from1.8ns to6.67ns with the pump power, when the peak power of the pulse almost remains unchanged. At the same time, the pulses and spectrum at different output position have been compared when the pulses transmit in the fiber, which conform to the theory that pulses will be shorten when transmit in anomalous region. Meanwhile, high peak power of8.29W has been successfully obtained by changing the output ratio in the cavity.The innovative work and results in this thesis are as follows: 1. A method of gain joint to generate fiber laser of C+L band has been proposed and demonstrated. The spectrum with3dB bandwidth of60nm has a flat top. The method makes it possible to further decrease the nonlinear chirp of the pulse and shorten the pulse width.2. A method by taking advantages of high nonlinear fiber to generate square pulses with tunable pulse width in a cavity shorter than30m has been proposed and demonstrated. On the one hand, the ultra-broadband spectrum of80nm has been achieved in frequency domain. On the other hand, high peak power of8.29W has been generated by changing output ration in the cavity.