Study On The Output Properties Of Fiber Lasers Operating Near980nm

Fiber lasers have been a focus of recent researches due to their great potentials toimprove the brightness of laser sources. One outstanding realization is the10kWsingle-mode tandem pumped fiber lasers fabricated by IPG Corp. in2009. However,further enhancement of the output power of the fiber lasers is blocked by the lowerpump absorption in1018nm pumping wavelength. The fiber laser operating near980nm can replace the1018nm fiber lasers to be the high brightness tandem pumpingsource for the high absorption cross-section at980nm region in Yb-doped fibers, beingof great interest. However, the realization of the high brightness980nm fiber lasers islimited by the effect of amplified spontaneous emission (ASE). Thus, in this thesis, theouput properties of980nm fiber laser is theoretically, numerically and experimentallystudied systematically to explore the suppression of the ASE to promote the outputpower and efficiency of the laser. The main contents are as follows:1. The theoretical model of980nm fiber laser has been established to discuss andanalyze the output properties of the980nm fiber laser. The threshold condition of980nm lasing is obtained, so as the relation of the1030nm gain with the980nm gain andthe915nm negative gain. It is found that enlarging of the core/cladding ratio of the gainfiber is an effective way to suppress the ASE to improve the output power and efficientof the980nm fiber laser.2. The influencing factors on the output properties of980nm fiber laser aresestematically and numerically analized and some important conclusions are achievedas below:①the effect of the fiber length on the output properties of980nm fiber laseris studied. It is found that the lengthening of the gain fiber may lead to two peak valueof the output powers, Attributed to the gain competition of two lasing wavelengths.②corresponding to the same core/cladding ratio, the active fiber with larger core diameterproduces a lower lasing power than the one with smaller core diameter.③theexponetional increment of the pump threshold with the fiber length is numericallyacquired, and the relation can be expressed asPp th (L) exp k p apN (L L0) P0.④it is important to make sure the FBG owns enough SLSR to suppress the ASE, but notnecessary to make the SLSR of the FBG as large as possible.⑤with the increase of thespectral width of the FBGs, the output power decreases at first and then increases, whilethe lasing wavelength is red-shifted.3. The all fiber980nm fiber laser is experimentally set-up to study on the outputproperties and validate the conclusions acquired by simulations. The effect of pumppower on the output properties of the980nm fiber laser is obtained and it turns out tomatch the results get from the simulation. Moreover, the phenomenon, the signal power reaches it peak twice on the cource that the gain fiber length increases, is observed inthe experiment. In addition, the exponetional relation of the pump threshold with thefiber length is also obtained by experimental means.4. The dual-ward-feedback pumping scheme, which is beneficial to boost theoutput power and efficiency of980nm fiber laser, is promoted and two possibleexperimental performances are also put forward. By numerical analysis, it is found thatthe output signal power of the980nm fiber laser under this pumping scheme isapproximately5-times larger than that of the980nm fiber laser under forward pumpingscheme.