Femtosecond fiber lasers and amplifiers based on the pulse propagation at normal dispersion

Abstract

The applications of ultrafast optical pulses exploded in last two decade since the discovery of a mode-locked Ti:sapphire laser. Ti:Sapphire lasers are great ultrafast optical pulse sources but they are not suitable for some applications since they are are bulky, expensive, and unreliable. So far, solid-state lasers including Ti:sapphire lasers are dominant as ultrafast pulse sources. However, compact, inexpensive and stable fiber lasers recently started to replace solid-state lasers. Even though fiber lasers have many practical advantages, the performance of fiber lasers is still below that of the solid-state fiber lasers. Among many kinds of fiber lasers, a mode-locked ytterbium (Yb)-doped fiber lasers has been received a broad attention for medical applications such as the biomedical imaging. This thesis summarizes the e ort of the Yb-doped fiber laser performance enhancement utilizing the pulse propagation at high normal dispersion. In this thesis, femtosecond Yb-doped fiber lasers without anomalous dispersion element, so called all-normal-dispersion (ANDi) fiber lasers, are demonstrated based on unique pulse shaping mechanism of the chirped pulse spectral filtering. ANDi fiber lasers represent a new paradigm for femtosecond pulse generation. This new type of a laser is very practical because it avoids the technical challenges of providing anomalous dispersion without loss at 1um. Useful features of the ANDi fiber lasers have been demonstrated experimentally in terms of the pulse energy, the pulse duration, the environmentally stability, and controllable multipulsing states. Pulse energies > 20 nJ with >100 kW peak power and pulse durations <100 fs are experimentally demonstrated. Theoretical studies indicate that further performance improvement is quite possible. The ANDi fiber lasers are not only practical femtosecond lasers, but also great research tools for ultrashort pulse propagation phenomena. Dissipative solitons of complex cubic quintic Ginzburg-Landau equation are demonstrated experimentally from an all-normal dispersion fiber laser. This thesis is not limited to the demonstration of ANDi lasers. It also covers interesting pulse propagation phenomena in fiber lasers and amplifiers. The formation of a second-order dispersion managed soliton, which is referred as an antisymmetric dispersion managed soliton, in a fiber laser with a strong dispersion map is demonstrated. Finally, the thesis describes the chirped-pulse-amplification system performance enhancement with proper nonlinear phase shift and third-order dispersion.