The Fabrication,Characterization And Application Of Yb³⁺-Doped SiO₂-Al₂O₃-Y₂O₃ Fibers

Single-frequency（Single-longitudinal mode）fiber lasers lasers have attracted much attention for their applications in coherent optical communication,distributed optical fiber sensors,coherent lidar,microwave and THz wave generation.Since gain fibers are the key components of the fiber lasers,the selection of material and preparation of fiber would affect the performances of the lasers.Although great progress has been made in the exploration of highly doped phosphate and germanate fibers,it is still of great significance to explore new gain media for the development of single-frequency fiber lasers.The SiO₂-Al₂O₃-Y₂O₃ fibers have been successfully fabricated using YAG as core material.The fibers have high thermal conductivity and low Brillouin gain coefficient.At the same time,Yb³⁺in the fibers can simply replace the position of Y³⁺without destroying the network structure of the material itself.And It is beneficial to obtain high unit length gain by increasing rare earth doping concentration（more than 20 wt%）.Using Yb³⁺-doped SiO₂-Al₂O₃-Y₂O₃ fiber as gain medium is beneficial to build high efficiency single-frequency fiber laser.In this paper,the fabrication and optical proper-ties of Yb³⁺-doped SiO₂-Al₂O₃-Y₂O₃ fiber,and design of fiber laser are studied experi-mentally.1.Using Yb³⁺-doped YAG crystal rods as core materials,Yb³⁺-doped SiO₂-Al₂O₃-Y₂O₃ fibers with 3.26 wt%concentration were successfully fabricated by using a melt core method.The Yb³⁺doped SiO₂-Al₂O₃-Y₂O₃ fiber has a core diameter of⁶.5μm.The transmission loss of⁰.0085 dB/cm@1560 nm was measured by using a cutback method.The absorption and emission cross sections of the fiber were calculated.The result shows that the absorption and emission cross sections of the optical fiber are better than those of the silica and phosphate fibers,which is beneficial to build high efficiency fiber lasers.2.The unit gain of gain fiber is an important parameter for rare-earth fiber laser.The gain characteristics of Yb³⁺-doped SiO₂-Al₂O₃-Y₂O₃ fiber was measured.The obtained unit gain of fiber was 3.9 dB/cm,which was comparable to Yb³⁺-doped phosphate glass fiber.And no obvious darkening phenomenon was observed during the experiment.The result shows that the fiber is a potential gain medium of fiber lasers.3.Uing 1 cm long Yb³⁺-doped SiO₂-Al₂O₃-Y₂O₃ fiber as gain medium and 99%and 68%Bragg gratings as reflectors respectively,a short linear cavity fiber laser was constructed.The output laser with a central wavelength of 1036.1 nm was obtained,the slope efficiency was 5.2%.The experimental result shows that the fiber is expected to be used in the development of single-frequency fiber lasers.We also used Yb³⁺-doped SiO₂-Al₂O₃-Y₂O₃ fiber and carbon nanotube（CNT）saturable absorber as gain medium and mode-locked device to build a ring cavity mode-locked laser.A stable mode-locked laser output was obtained.The threshold of mode-locked laser output was 42.5 mW.The laser slope efficiency,pulse interval,repetition rate and pulsewidth were 4.4%,34 ns,25.5 MHz and 680 ps respectively.