Research On The Thermal Effect On Cavity-assisted-pumping Er/Yb Codoped Optical Fiber Amplifiers

Er/Yb-codoped double-cladding fiber amplifier(EYDFA)can be used to amplify the laser light with a wave at around 1.5 ?m.The laser light at this band not only has low loss propagating in fibers and in atmosphere,but also has a relatively eye safe characteristics.In recent years,with the development of laser welding,laser industry,and space optical communication etc.high-power lasers in the band have been urgently needed.And we found that the Yb-band amplified spontaneous emission is the main obstacle to the development of high power EYDFA.To solve the problem,our research group proposed the Yb-cavity-assisted-pumping EYDFA.Compared with ordinary EYDFA,the Yb-cavity-assisted-pumping EYDFA not only has higher pump power conversion efficiency and better gain flatness but also has a shorter optimal gain fiber length to avoid harmful nonlinear effects.Due to the high-Q of the cavity,the excessive energy accumulated in the Yb-band at a high pump power is almost closed in the cavity as Yb-band oscillations,which causes the thermal effect of the Yb-cavity co-pumped EYDFA more serious than an ordinary EYDFA.Thermal effect has crucial influence on the performance of the amplifier and even damages the amplifier.In order to achieve high-power output,thermal effect on the Yb-cavity co-pumped EYDFA has been investigated in this thesis.A numerical simulation model of Yb-cavity co-pumped EYDFAs considering the thermal effect has been established to investigate the thermal effect on the amplifier,and the results have been confirmed by experiments.The main achievements in this thesis are as follows:1.We proposed a new method for the determination of the positions of Stark levels of the rare-earth ions.Based on the absorption and emission cross-section spectra of rare earth ions measured at a certain temperature and McCumber theory,a numerical optimization method was porposed to retrieve positions of Stark levels.2.Thermal effect on the emission and absorption cross-section spectra has been investigated.And we find that in the region around the pump wavelength,the absorption cross sections decrease with the increasing temperature which results in a decrease in the absorption efficiency of the pump light in the gain fiber.3.The numerical simulation model of Yb-cavity co-pumped EYDFAs considering the thermal effect has been established to theoretically investigate the thermal effect on the amplifiers performance.Thermal effect on the output power,optimal fiber length,and the selection of the resonant wavelength of the cavity are investigated through numerical simulations which provides a reference for the design of the Yb-cavity co-pumped erbium/ytterbium-codoped fiber amplifier.4.Experimental research on the Yb-cavity co-pumped EYDFAs was carried out.The axial temperature distribution,output power and spectral characteristics of the fiber amplifier were measured experimentally.The experimental results show that the Yb-band oscillation in the cavity can make the temperature distribution along the fiber amplifier more uniform,which is beneficial to reduce the maximum temperature of the fiber amplifier.