Study On The Spectral Performance Of Yb³⁺ Doped Silica Fiber For 1018 Nm Tandem-pumping Technology

As the mainstream direction of future development,high power fiber laser has always been a research hotspot,and has a very wide range of applications in industrial processing,medical treatment,national defense and other fields.The 1018nm co-band pumped Yb³⁺doped silica glass fiber laser(YDFL)is one of the effective methods to reach its output limit,mainly because the1018nm co-band pumped technology has the advantages of good beam quality,high brightness,small quantum loss,and effective suppression of high-order mode gain.However,the progress of fiber laser technology also puts forward more stringent requirements for fiber performance.At present,MCVD method adopted by the mainstream commercial optical fiber are severely limited in the fiber core size,doping uniformity and numerical aperture,and sol-gel method in combination with nano powder sintering technology developed by our team can prepare rare earth doped quartz glass with large size and high doping concentration,which can be used for large mode field optical fiber and solid double frequency laser.Based on this preparation technique,a series of Yb³⁺doped quartz glass samples were prepared through further optimization and improvement,and the microstructure and 1018 nm spectral characteristics of Yb³⁺doped silica glass were systematically studied,which provided an important reference for the development of 1018 nm trandem pumped Yb³⁺doped quartz optical fiber.The details of this paper are as follows:Three types of Yb-Al(YA),Yb-Al-P(YAP)and Yb-P(YP)co-doped silica glass systems were prepared by a novel sol-gel method combined with a high-temperature sintering process of nanopowders,and the effects of variations in Al³⁺and P⁵⁺contents on the absorption and fluorescence properties of Yb³⁺doped silica glasses at 1018 nm were initially investigated internationally.We can find that,with the doped P⁵⁺content increasing,the fluorescence sub-peak near 1030 nm blue shifts to around 1018 nm,and the normalized fluorescence intensity of Yb-P series samples is significantly superior to others at 1018 nm through normalized lateral comparison of the 1018 nm spectral performance under different doping systems.A kind of high transparent silica based nanocrystalline glass with excellent spectral properties was prepared by a new high temperature sintering process of sol-gel and nanometer powders.HRTEM shows that the size of Yb:YAG nanocrystals in the glass is about 30 nm,and they are uniformly dispersed in the amorphous silicon glass matrix.By comparing the spectral properties with those of glass samples,it is proved that the low content nanocrystalline glass has a great advantage in spectral properties.Compared with Yb³⁺doped quartz glass,the absorption cross section and emission cross section of Yb:YAG nanocrystalline glass near 1018 nm are greatly improved by?80%,which makes it a promising near infrared laser material for further application in the field of high power laser.A novel sol-gel method combined with a nanopowder high-temperature sintering process was used to prepare and study the structure and spectra of Yb-Er-P co-doped silica glasses,and the Yb?Er energy transfer was most favorable when the Yb/Er doping ratio was 5 times.In addition,high phosphorus(P)doping results in the Yb³⁺ions and Er³⁺ions being mainly surrounded by P atoms.The high phosphorus(P)doping also results in the formation of P=O double bonds,which increases phonon energy of silica glass to 1320 cm^-1.The higher phonon energy leads to a significant reduction of the Er³⁺:⁴I_11/2 energy level lifetime,which significantly suppresses the reverse energy transfer from Er³⁺ions to Yb³⁺ions and effectively enhances the energy transfer efficiency from Yb³⁺ions to Er³⁺ions.The high-level phosphorus(P)doping increases the solubility of Yb³⁺ions and Er³⁺ions in the glass matrix,effectively avoiding the clustering phenomenon caused by the high doping of rare earths.