Investigation Of 1.0μm High Power Wideband Square-wave Pulse Fiber Laser

In recent years, fiber lasers with advantages of high efficiency, compact structure, working stably, obtain a more widely application in academic and industrial fields. Nanosecond square-wave pulse has been paid much attention due to its unique properties at the temporal and frequency domain in communication, laser display, medical fields as well as research on the basic principles of the square-wave pulse. In this thesis, the high power wide band square-wave pulse fiber laser at 1.0 μm is investigated, including its properties in the temporal and frequency domain.The major results in the thesis are obtained as follows.1. A wideband and stable mode-locked all-polarization-maintaining fiber laser using a nonlinear optical loop mirror (NOLM) is obtained in experiment. The central wavelength of the laser is 1080.14 nm and the 3 dB bandwidth is 20.29 nm. The repetition rate of the pulse is 3.28 MHz and the pulse width is 848 ps. By tuning the pump power, which is centered at 980 nm, from 300 mW to 380 mW, we obtained a linearly changed output power from 6 mW to 7.12 mW.2. Based on the nonlinear amplifying loop mirror (NALM), the high power pump source of laser diode centered at 915 nm and the ytterbium-doped double-clad fiber (Yb-DCF) as gain fiber, we obtained the high power wide band square-wave pulse with 3 dB spectrum bandwidth 6.5 nm, central wavelength 1083.65 nm, the maximum average output power 1.31 W and peak power 40 W. Furthermore, the square-wave pulses could be tuned from 4.79 ns to 14.43 ns.3. By changing the length of the inserting single mode fiber (SMF) in the NALM loop, we always obtained the stable square-wave pulse. Meanwhile, with the length of the SMF changed in the NALM loop, the output spectrum got narrower, varying from 6.5 nm to 0.08 nm.The innovative work and results in this thesis are as follows.1. Different from the common way to generate square-wave pulse with the nonlinear polarization rotation (NPR) at 1.5 μm, ytterbium-doped double-clad fiber with high absorption efficiency was used to generate the high power wide band square-wave pulse. The 3 dB spectrum bandwidth was 6.5 nm. To the best of our knowledge, this is the widest output bandwidth in a square-wave pulse fiber laser operating at 1.0 μm.2. By changing the length of the inserting SMF in the NALM loop, we obtained the stable square-wave pulse with 3 dB bandwidth varying from 6.5 nm to 0.08 nm.