Study On High Power 1150nm Fiber Laser

In recent years, fiber lasers emitting at 1120~1200 nm have broad applications in the military, astronomy and medical fields. Yb-doped fiber is the most common gain medium, but the power is limited to amplified spontaneous emission around 1060~1100 nm since the emission cross-section around 1120~1200 nm is very small. In order to overcome this difficulty, theoretical and experimental work has been carried on in this paper, and the results are as follows:Firstly, this paper presents the theoretical model of ytterbium-doped fiber laser at 1120~1200 nm to give a systematic analysis on the laser. According to the absorption and emission properties of ytterbium ions, the influence on output characteristics are analyzed in all kinds of factors, such as the feedback of ASE, the reflectivity of fiber Bragg grating, fiber parameters, pumping direction, and background loss. Based on the theory, we design the optimized parameters and carried on an experiment, which is Yb-doped fiber laser emitting at 1150 nm directly pumped by laser diode. A maximal output power of 52 W was achieved, and to the best of our knowledge, it is the highest power at this wavelength.Secondly, in order to avoid the limit of parasitic oscillation in power promoting of Yb-doped fiber laser at 1150 nm, Raman gain comes into consideration. A theoretical model of Raman fiber laser is established to analyze the influence of fiber length, reflectivity of fiber Bragg grating, Raman gain coefficient and signal loss on the output characteristics. Depending on the results of theory, we set up a Raman fiber laser at 1150 nm. The output power of 144 W at 1150 nm was achieved, and to the best of our knowledge, it is the highest power at this wavelength. Besides, pulsed fiber laser at 1150 nm was also achived, and it is the first time to realize a pulsed laser at this wavelength.Thirdly, since the Raman fiber laser is tandem pumped, the structure is complicated and the overall efficiency is low. On the foundation of superiority of Raman gain, a new method is put forward, which is fiber laser based on the compound cavity structure. Since it is pumped directly by laser diode, the structure is simple and the overall efficiency is high, relatively. Besides, the Raman gain makes to the suppression of ASE and parasitic oscillation.