Fabrication And Characterization Of Er³⁺:Yb³⁺ Co-doped Phosphosilicate Fibers

With the rapid development of high data rate optical communication system, highpower (>1W) optical fiber amplifiers, compatible with high data rate channels spreadingover the1530nm-1565nm (C-) band spectrum, are of great interest in applications suchas nonlinear signal processing and optical data transport. Recently, withytterbium-sensitization, the optical pump excites the erbium(Er) ions indirectly, via energytransfer from ytterbium(Yb) ions, cladding pumped EYDF amplifiers (EYDFA) haveattracted considerable attention to achieve high power levels. Thus, fabrication process ofYb/Er co-doped fibers by modified chemical vapor deposition (MCVD) becomes theresearch focus.Fabrication process of efficient Er/Yb co-doped phosphosilicate fibers by MCVD isreported in this paper. The process is combined with the solution doping technique wherethe co-dopant of aluminum is absolutely removed. Fabrication process of Er/Yb co-dopedphosphosilicate fiber preform by MCVD, which is combined with the backwarddeposition process is described in details. It shows that the backward deposition processcan be adapted to incorporate low viscosity phosphate glass and the reason of the porouslayer with a higher phosphorus content which is fabricated in that process is also discussed.The limiting of the back-transfer of energy from Er ions to Yb ions and the suppressingthe onset of Yb-ASE are demonstrated by fluorescence spectrum of the perform ofphosphosilicate.Finally, the performances of double-cladding Er/Yb co-doped fiber lasers(EY-DCFLs) are studied experimentally. Then, the effect of the ytterbium to erbiumconcentration ratio and different fiber lengths on the laser characteristics are discussed.The maximum output power of EY008is about3.2W by using a4m fiber, with a slopeefficiency of30%. It shows the efficient energy transfer only with low concentration rareearths in this ytterbium-sensitized erbium fiber, because of high concentration rare-earthions cluster in low P2O5concentration region.