Qinling Zhou

Influence of Al3+ and P5+ ion contents on the valence state of Yb3+ ions and the dispersion effect of Al3+ and P5+ ions on Yb3+ ions in silica glass

Three series of Yb3+-doped silica glasses containing different amounts of Al2O3 and P2O5 were prepared successfully by using a sol–gel method. Absorption, excitation and fluorescence spectra of Yb2+ ions in these silica glasses as well as X-ray photoelectron spectra (XPS) of Yb4d were recorded and analysed systematically. It is found out that the addition of Al3+ or P5+ ions has great influence on the redox state of ytterbium ions. With increasing Al3+ ion contents in these silica glasses, more trivalent Yb3+ ions are reduced to divalent Yb2+. In contrast, the increase of P5+ ion contents greatly promotes divalent Yb2+ ions to be oxidized to trivalent Yb3+. The possible redox mechanisms have been explored and discussed in detail. The influence of Al3+ and P5+ ion contents on the near-infrared luminescence intensity of Yb3+ ions and cooperative luminescence of Yb3+ ion pairs was also discussed. Both the near-infrared luminescence intensity of Yb3+ ions and cooperative luminescence of Yb3+ ion pairs decrease gradually with increasing Al3+ and P5+ ion contents. The decrease of cooperative luminescence of Yb3+ ion pairs indicates a good dispersion effect of Al3+ and P5+ ions on Yb3+ ions in Yb3+-doped silica glass. The results are useful for optimization of fabrication of the high quality Yb3+-doped silica fiber by the composite design of Yb–Al–P co-doped silica glass.

Neodymium-doped phosphate fiber lasers with an all-solid microstructured inner cladding

We report on high-power fiber lasers based on index-guiding, all-solid neodymium-doped (Nd-doped) phosphate photonic crystal fiber (PCF) with a hexagonal-shaped inner cladding. The optimum fiber laser with a 36 cm length active fiber, generated up to 7.92 W output power at 1053 nm, which benefited from a high absorption coefficient for pump power due to its noncircular inner cladding. The guiding properties of the all-solid PCF were also investigated. A stable mode with a donut-shaped profile and a power-dependent laser beam quality have been observed experimentally and analyzed.

Watt-level Yb-doped silica glass fiber laser with a core made by sol-gel method

A Yb-doped silica glass fiber laser with a core made by sol-gel method is reported. The maximum power of 1.14 W is obtained with a pump power of 5.46 W at a wavelength of 976 nm. The slope efficiency is 34%. The refractive index fluctuation across the core is below 5×10-4 at a doping level of Yb 0.15 mol%, A2O3 4.0 mol%, and P2O5 2.0 mol%. High background attenuation of 6 dB/m at 1 053 nm limites the slope efficiency and maximum output power.

Cooperative Quantum Cutting in Yb

Quantum cutting down-conversion (DC) with the emission of two near-infrared photons for each blue photon absorbed is realized in Yb -Tb codoped borosilicate glasses. With the excitation of Tb ion by a 484-nm monochromatic light, emission from the F F transition of Yb ions is observed and this emission is proved to originate from the DC between Tb ions and Yb ions. Results shows that maximum quantum efficiency reach as high as 153%, which is comparable with that in oxyfluoride glass ceramics in this system. With the advantages of excellent transparence, easy shaping, good stability, and low cost, Yb -Tb codoped borosilicate glasses are poten- tially used as down-converter layer in silicon-based solar cells. Index Terms—Optical glass, photovoltaic cells, quantum cutting (QC), Yb -Tb .

^{3+}

We report experimental results on high-power heavily Nd-doped phosphate continuous-wave (CW) fiber lasers of very short length. The optimum fiber laser with a length of 26 cm exhibited a maximum output power of as much as 2.87 W and a slope efficiency of 44.7% with respect to absorbed pump power at 795 nm. Up to 1-W laser was also obtained from a 6-cm-short active fiber. The fiber lasers were demonstrated at 1053 nm with a linewidth of 1.6 nm, and showed no evidence of roll-over even at highest output power. The output powers were stable and limited only by available pump power.

–Tb

The absorption and emission properties of Yb3+ doped oxy-fluoride-silicate glasses prepared by the melt-quenching method have been investigated. Yb3+ ions in the oxy-fluoride-silicate glasses show large absorption and emission cross-section and the fluorescence lifetimes are longer than 1.3?ms. The minimum pumping intensity, minimum fraction of excited ions, saturation pumping intensity, minimum pulse duration and peak power are also analysed to characterize the samples. The minimum pulse duration and peak power are 79?fs and 0.432?PW?cm?2, which indicates the potential application in high power and ultrashort pulse lasers.

^{3+}

This paper reports, for the first time to our best knowledge, a nearly diffraction-limited output in a Yb(3+)/Al(3+)/F(-) codoped double cladding silica fiber with a 50 μm core diameter and 0.02 core NA. The core glass with a diameter >6  mm was fabricated through solgel process combined with high temperature sintering. Laser performances of this fiber at different bend diameters were studied. The mean M2<1.1 in this 50 μm core diameter fiber was achieved at a bend diameter of 0.35 m. The core glass with the refractive index nearly equal to pure silica glass is suitable for the fiber design, such as large-mode-area photonic crystal fiber.

Codoped Borosilicate Glasses

Tm3+-doped 0.1Tm2O3-1Al2O3-98.9SiO2 (mol%) silica glass with good uniformity was prepared by sol-gel method combining with high temperature sintering. The core glass sized Φ3.2 × 50 mm with Δn of 5 × 10−4 was obtained after gelation, heat treatment, melting and polishing. Its spectroscopic properties were evaluated according to the detected absorption and fluorescence spectra. The maximum emission cross-section of Tm3+ ion in this glass is 6.2 × 10−21 cm2 and tested fluorescence lifetime is 836 μs at 1806 nm. Large core double cladding fiber with core NA of 0.102 was prepared by rod-in-tube and high temperature drawing. Its tested optical loss is 1.1 dB/m at 1333 nm. 1.11 W fiber laser output centered at 1969 nm with M2 factor of 1.99 was obtained from a 140 cm length double-cladding fiber with core diameter of 38 μm. The quasi-single mode laser with M2 factor of 1.33 was achieved in the fiber with core diameter of 19 μm.

Efficient Generation of Watt-Level Output From Short-Length Nd-Doped Phosphate Fiber Lasers

Based on the sintering of ytterbium-doped nanoporous glass, a nonchemical vapor deposition process aimed at fabricating a large-mode area of photonic crystal fibers has been proposed for the preparation of active silica glass. With the relatively low doping concentration and boron in the silica glass as benefits, a close refractive index between the core and the cladding was obtained. The refractive index variation indicated good homogeneity of the doped fiber core. Up to 34.8 W laser output was demonstrated with the PCF laser and the slope efficiency was 71.3%. The output laser beam quality had slightly multimode behavior, with a mean M 2 of 2.42.

Optical properties of Yb3+ ions in SiO2?Al2O3?CaF2 glasses

We demonstrate an all-solid Nd 3+-doped silicate photonic crystal fiber with 13.1 W output power at 1061 nm and 64.5% slope efficiency. We also theoretically investigate and prove the effects of confinement loss and overlap fraction on a double-clad photonic crystal fiber laser. An innovative design is suggested to improve the laser beam quality.