Yb-doped Aluminophosphosilicate Fiber Research Articles

Optical cooling of a Yb-doped alumino-phosphosilicate fiber in air by -250 mK.

Recent progress in the fabrication of Yb-doped silicate fibers with low concentration quenching and low background absorption loss has led to the demonstration of anti-Stokes-fluorescence cooling in several aluminosilicate compositions. This breakthrough is critical to combat deleterious thermal effects due to the quantum defect in fiber lasers and amplifiers. Since cooling efficiencies remain low (1-2.7%), it is paramount to engineer compositions that improve this metric. We report a silica fiber with a core glass heavily doped with aluminum and phosphorus that sets, to our knowledge, a few new records. This few-mode fiber (16-µm core) was cooled in air by -0.25 K from room temperature with ∼0.5 W of 1040-nm power. The measured cooling efficiency is 3.3% at low pump power and 2.8% at the power that produced maximum cooling. The critical quenching concentration inferred from the measured dependence of cooling on pump power and careful calibration of the pump absorption and saturation is 79 wt.%. The inferred background absorption loss is 15 dB/km. Together with the fiber's average Yb concentration of 4.2 wt.%, these metrics rank among the best reported in a silica glass.

Yb-doped aluminophosphosilicate fiber amplifier with 244 pm linewidth and near diffraction limited beam quality for beam combination

Yb-doped aluminophosphosilicate fiber was fabricated by the combination system of chelate precursor doping technique and the modified chemical vapor deposition system. The technical details of the fabrication process were optimized to ensure the same elemental concentration ratio of Al/P. The capability of this fiber for the beam combining application was investigated based on a narrow linewidth fiber laser system. This fiber presented the output power of 1783 W with a slope efficiency of 83.7 % and a 20 dB root-mean-square linewidth of 0.244 nm with no nonlinear effects in the laser spectrum. Near-diffraction-limited beam quality was also observed with a M2 factor less than 1.27. In conclusion, this fiber presented an attractive laser performance for beam combination through the comprehensive optimization of fabrication technique and narrow linewidth laser system.

Comparative study of γ-radiation resistance between Yb/Ce/F and Yb/P doped aluminosilicate fibers

To quantitatively compare the radiation resistance of Ytterbium/Cerium/Fluorine(Yb/Ce/F)-codoped aluminosilicate and Yb-doped aluminophosphosilicate fibers in an ionizing radiation environment, we fabricated these two kinds of samples by applying the modified chemical vapor deposition system combined with chelate precursor doping technique. When the radiation dose accumulated to 200 Gy, the radiation-induced transmission attenuation of Yb-doped aluminophosphosilicate fiber is approximately 2.8 times that of the Yb/Ce/F-codoped aluminosilicate fiber. At this dose level, the slope efficiency of Yb/Ce/F-codoped sample decreased to 1/2 of the non-radiated efficiency value, while the other sample dropped to 1/20. The results demonstrate that Yb/Ce/F-codoped fibers are much more suitable for application in a radiated environment.

10 kW-level Output power from a Tandem- pumped Yb-doped aluminophosphosilicate fiber amplifier

In this paper, we present a 10 kW-level output power fiber amplifier based on tandem-pumping. The characteristics of active fiber for amplifier stage is reported. To ensure adequate absorption of tandem pumping light in relatively short fiber length, a large-scale Yb3+ doped aluminophosphosilicate (Al2O3-P2O5-SiO2, APS) fiber with 50 μm core and 400 μm inner-clad in diameter, i.e., a 50/400 Yb-APS fiber, was theoretically designed and experimentally fabricated by using modified chemical vapor deposition system combined with chelate precursor doping technique. The measurements showed that the dopant concentration of Yb2O3, Al2O3, and P2O5 was estimated to be 0.17 mol%, 1.4 mol%, and 1.5 mol%, respectively, and the absorption coefficient of the fiber was about 0.77 dB/m at 1018 nm. The amplifier stage with this 40 m Yb-APS fiber tandem-pumped by 1018 nm fiber laser, delivered 9.82 kW laser output at 1080.08 nm with an optical-to optical efficiency of 86.8%. The knowledge of the characteristics of the Yb3+ doped APS fiber can usefully guide future design of high output power fiber amplifier based on tandem pumping.

Fabrication and laser performance of triple-clad Yb-doped aluminophosphosilicate fiber

Abstract We fabricated an Yb-doped triple-clad fiber consisting in adding to aluminophosphosilicate core and F300-pump cladding, low-refractive-index fluorine doped silica cladding, and demonstrated its laser performance based on an all-fiber oscillator. MCVD system, all-gas-phase chelate precursor doping technique, and a simple overcladding process were applied to make Yb-doped aluminophosphosilicate triple-clad fiber preform. Ultra-thin substrate tube and a two-stage deposition process were proposed to decrease and offset elements evaporation. The outer region of fiber core was tested with ∼1050 ppm Yb2O3, ∼10,800 ppm Al2O3, and ∼9950 ppm P2O5, while the central region was doped with ∼600 ppm Yb2O3, 8100 ppm Al2O3, and ∼7000 ppm P2O5, respectively (ppm is in molar here). Two-stage deposition process and triple-clad design results in pump absorption from Yb3+ ions about 0.67 dB/m at 915 nm. Tested in an all-fiber oscillator configuration forward-pumped by 915 nm laser diodes, 28 m-long triple-clad fiber presented 560 W laser output with optical-to-optical efficiency of 68.7%, and the corresponding beam quality M2 is ∼1.18. The results indicate all-gas-phase chelate precursor doping technique in combination with overcladding technique is potential to manufacture high power triple-clad fiber, and ultra-thin substrate tube as well as two-stage deposition process are very effective ways to decrease and offset element evaporation.

3 kW 20/400 Yb-Doped Aluminophosphosilicate Fiber With High Stability

By using the MCVD system and the all-gas-phase chelate precursor doping technique, we fabricated an Yb-doped aluminophosphosilicate fiber with 20 μm-core and 400 μm-clad in diameter, i.e., 20/400 Yb-APS fiber. The fiber core was doped with 1100 ppm Yb3+, 7200 ppm Al3+, and 8000 ppm P5+. With a molar ratio of Al/P close to 1:1, low refractive index difference and suitable numerical aperture was obtained for large-mode-area fiber design. Directly forward pumped by 976 nm laser diodes, 11-m-long 20/400 Yb-APS fiber presented 3.03 kW laser output at 1080 nm with a slope efficiency of 76.6% and beam quality M2 of ∼1.58. Up to this power level, no signs of instable beam profile, beam quality worsening, and laser power roll-over were obtained, indirectly justified no obvious mode instability in the whole laser setup. To directly characterize its power stability and photodarkening effect, the fiber laser was kept at ∼2.1 kW for over 500 min with power degradation less than 1.1%. These results indicated that the all-gas-phase chelate precursor doping technique is highly competitive for Yb-APS fiber fabrication toward high-power laser, and the fabricated fiber is very suitable for 2 kW-level or above commercial fiber laser development.

Multi-kW Yb-doped aluminophosphosilicate fiber

For directly characterizing photodarkening effects, we demonstrated long-term laser stability of a 5kW-level fiber amplifier based on a Yb-doped aluminophosphosilicate fiber with a 30µm-core and 600µm-clad. The molar ratio of Al3+/P5+ was designed to be 1.1 ± 0.05 for remarkable photodarkening suppression, suitable numerical aperture, and central dip mitigation of refractive index profile. A modified chemical vapor deposition system combined with an all-gas-phase chelate precursor doping technique was applied to fabricate this fiber, doped with 0.15mol% Yb2O3, 1.7mol% Al2O3, and 1.4mol% P2O5. Tested at a master oscillator power amplifier laser setup, the 18m-long 30/600 Yb-doped aluminophosphosilicate fiber allowed for 6.14kW aggregated pump power at 976nm, and then showed a 5.19kW laser output at 1064.4nm with a high optical-to-optical efficiency of 85.2%. Up to this power level, an output spectrum without any sign of stimulated Raman scattering and amplified spontaneous emission was obtained. The fiber amplifier setup was kept at a 5.16kW output for over 600 minutes without power degradation, justifying a remarkable suppression of photodarkening. The results indicated that the all-gas-phase chelate precursor doping technique is highly competitive for low-photodarkening Yb-doped aluminophosphosilicate fiber fabrication towards a 5kW-level commercial high-power laser.

30/900 Yb-doped Aluminophosphosilicate Fiber Presenting 6.85-kW Laser Output Pumped With Commercial 976-nm Laser Diodes

To incorporate sufficient pumping power, a large-scale Yb-doped aluminophosphosilicate (Al2O3 -P2O5-SiO2, APS) fiber with 30- μ m core and 900- μ m inner clad in diameter, i.e., a 30/900 Yb-APS fiber, was theoretically designed and experimentally fabricated by using modified chemical vapor deposition system combining with chelate precursor doping technique. Analyzed by an electron probe microanalyzer, the dopant concentration of Yb2O3, Al2O 3, and P2O5 was estimated to be 0.14 mol%, 1.1 mol%, and 1.4 mol%, respectively. Based on an all-fiberized master oscillator power-amplifier laser setup directly forward pumped by commercial 976-nm laser diodes, 6.85-kW laser output at 1079.79 nm was achieved with an optical-to-optical efficiency of 67.1%, and the beam factor of $M^{2}$ was 2.38. The results indicate that large-scale Yb-APS fiber is quite competitive for high-power fiber laser development.