The development of high power fiber laser and technologies are covered in this thesis. The first part of the thesis simulates the signal gain spectrum in an erbium-ytterbium fiber amplifier, which can be implemented in fiber laser systems to generate high power output. The second part proposes the use of gain-guided (GG) optical fibers to achieve high power mode-locked fiber lasers. The spatial-temporal pulse propagation in the GG fiber is simulated; self- focusing, and self-phase-modulation in this type of fiber is studied. The third part discusses phase- locked fiber laser designs. Self-imaging in optical fibers is simulated; the results provide a guide to the phase-locking fiber laser system design. The last part of the thesis investigates cylindrical vector (CV) beams generation from fiber laser system using a birefringent crystal. Radial and azimuthal polarization output can be switched very easily in this fiber cavity design. More interestingly, lasing with radial and azimuthal polarization can be achieved simultaneously. By introducing misalignment in the cavity, a beam with different polarization distributions is generated.