Yb～(3+)-doped Figure-of-eight Fiber Ultrashort Laser

As an important tool in physics, chemistry and life science studies, the ultrashort pulsed laser sources are on the edging of optical technology. Because of some of its inherited outstanding properties compared to the common solid-stated laser, the fiber lasers have already become a very active research region. The Er3+-doped ultrashort fiber laser is already very mature and good quality products are available on the market now. As an attractive gain medium the Yb3+-doped fiber has some better properties compared to the Er3+-doped fiber, such as higher saturable power, higher optical conversion efficiency and broader gain spectrum bandwidth (can support pulses as short as 30fs). In this paper the Yb3+-doped passively mode-locked fiber laser using the nonlinear optical loop mirror (NOLM) for mode-locking is studied experimentally and theoretically.At beginning, its development history, the newest achievement, the classification, the merits and shortcomings and also the application of the mode-locked fiber laser is summarized.Secondly, the basic mode-locking principles and technology of the fiber laser especially the figure-of-eight passively mode-locked fiber laser are introduced in detail. The differences between the passively mode-locked fiber lasers working in positive dispersion(Yb3+-doped) and negative dispersion(Er3+-doped) is discussed.Thirdly, through numerical simulation and experiments the properties of nonlinear optical loop mirror working in the positive dispersion region are studied and the effect of the length of NOLM on the pulse spectrum bandwidth is concluded. The design of the laser cavity is discussed. The laser cavities with or without dispersion compensation all were experimentally studied and the double wavelength phenomenon observed during experiments is discussed. The dynamics of the pulses in the cavity is studied experimentally. Finally, through the optimization of theparameters of the cavity, we achieved pulse duration 180fs and repetition rate 24MHz mode-locked pulse sequence output.