Optical properties of high power S-band fiber oscillators and amplifiers

S-band fiber lasers, one type of ytterbium doped fiber lasers(YDFLs) which emitting in the spectral region of 1010 nm similar to 1050 nm, have drawn more and more attention especially after the proposition of tandem pump fiber lasers. The S-band laser plays an important role as the pump in a tandem pumping scheme. However, high power S-band laser output is quite difficult because of severe re-absorption. Therefore, the optical properties of S-band fiber lasers are studied and methods to achieve high power S-band laser output are presented. An S-band laser emission model based on gain comparison is built for analyzing the mechanism of laser oscillation and amplification. The model is composed of rate equations and gain comparison of several wavelengths in ASE spectrum. The gain differential between laser wavelength and ASE peak wavelength is compared to the additional gain imposed by cavity mirrors in an oscillator or the seed in an amplifier. The comparison results help in concluding the feasibility of S-band laser emission. Based on the model, the influences of fiber properties (including core doping level, core -clad ratio, and fiber length), pump power and laser power on the operation of S-band fiber lasers or amplifiers are researched. The analysis shows that fibers with lower doping level, larger core-clad ratio and shorter length, seed with higher power, are more helpful in realizing high power S-band laser output. Also, the profile of oscillator is found more suitable in building high power S-band lasers than that of amplifier.