Yb-doped Aluminosilicate Research Articles

Laser performance and material characters of commercial Ce/Yb co-doped aluminosilicate binary glass fiber

To investigate the laser performance and material characters of Ce/Yb/F-codoped aluminosilicate binary glass fiber, we took commercial Nufern-20/400–9 M fiber as a research object. 1.83 kW laser output power at 1066 nm with an optical-to-optical efficiency of 81.7% was achieved in master oscillator power amplifier (MOPA) system. No power roll-over was found for about 1 h at the maximum power, indicating Nufern-20/400-9M fiber has excellent power stability. Ce3+ ions can effectively suppress the regular photodarkening phenomenon easily-observed in Yb-doped aluminosilicate glass fiber. However, as the laser output power exceeded 1 kW, optical nonlinearities, such as four-wave-mixing and stimulated Raman scattering, emerged and the beam quality factor M2 degraded heavily from 1.60 for 1 kW to 2.37 for 1.8 kW. The studying results show that Nufern-20/400-9M fiber with strong nonlinearities and low threshold of modal degradation in the MOPA system which is suitable for kW-level fiber laser applications.

Yb-doped large mode area fiber for beam quality improvement using local adiabatic tapers with reduced dopant diffusion.

A newly designed all-solid step-index Yb-doped aluminosilicate large mode area fiber for achieving high peak power at near diffraction limited beam quality with local adiabatic tapering is presented. The 45µm diameter fiber core and pump cladding consist of active/passively doped aluminosilicate glass produced by powder sinter technology (REPUSIL). A deliberate combination of innovative cladding and core materials was aspired to achieve low processing temperature reducing dopant diffusion during fiber fabrication, tapering and splicing. By developing a short adiabatic taper, robust seed coupling is achieved by using this Yb-doped LMA fiber as final stage of a nanosecond fiber Master Oscillator Power Amplifier (MOPA) system while maintaining near diffraction limited beam quality by preferential excitation of the fundamental mode. After application of a fiber-based endcap, the peak power could be scaled up to 375 kW with high beam quality and a measured M2 value of 1.3~1.7.

Yb-doped aluminophosphosilicate ternary fiber with high efficiency and excellent laser stability

Abstract By using chelate precursor doping technique and traditional modified chemical vapor deposition system, we fabricated Yb-doped aluminophosphosilicate (Al2O3-P2O5-SiO2, ternary Yb-APS) large-mode-area fiber and reported on its laser performance. The fiber preform was doped with Al, P and Yb with concentration of ∼8000 ppm, ∼1700 ppm and ∼400 ppm in molar percent, respectively. Tested with master oscillator power amplifier system, the home-made Yb-APS fiber was found to present 1.02 kW at 1061.1 nm with a high slope efficiency of 81.2% and excellent laser stability with power fluctuation less than ±1.1% for over 10 h. Compared with Yb-doped aluminosilicate (Al2O3-SiO2, binary Yb-AS) fiber, the introduction of P2O5 effectively suppressed photodarkening effect even the P/Al ratio is much less than 1, indicating that Yb-APS fiber is a better candidate for high power fiber lasers.

The Brillouin gain coefficient of Yb-doped aluminosilicate glass optical fibers

Provided herein is a detailed analysis of the Brillouin spectroscopy of the ytterbia (Yb2O3) dopant in aluminosilicate glass optical fibers. Yb-doped fiber lasers have become ubiquitous, and the results presented here may be used to design lasers and amplifiers for narrow linewidth systems and applications. It is found, with a high degree of certainty, that Yb2O3 has an acoustic velocity that is lower than that of silica, a Brillouin spectral width (or material acoustic damping coefficient) that is about 80 times greater than that of silica, and photoelastic constants (Pockels’ coefficients) that are negative. It is found that the primary influence of ytterbia in concentrations typical of active fibers is to broaden the Brillouin gain spectrum, thereby reducing the peak Brillouin gain. A set of design curves is provided outlining the Brillouin gain coefficient as a function of alumina concentration for several ytterbia concentrations, which can be utilized to design fiber structures with reduced Brillouin gain. The Yb-doped aluminosilicate fiber system is compared to the Yb-doped phosphosilicate system, and a high degree of similarity is found between them at low Al2O3 or P2O5 doping levels. However, for fiber produced utilizing conventional techniques, the phosphosilicates are found to have the potential for lower Brillouin gain since more P2O5 can be reliably incorporated into the glassy matrix.

High-efficiency fiber laser at 1018 nm using Yb-doped phosphosilicate fiber

A high-efficiency fiber laser at 1018 nm using homemade Yb-doped phosphosilicate fiber is demonstrated. The fiber shows blueshifted emission spectrum compared to Yb-doped aluminosilicate fiber, and is considered favorable for the short wavelength Yb-doped fiber laser. With a 7 m gain fiber, up to 22.8 W output at 1018 nm is achieved with an optical efficiency of 53%. The amplified spontaneous emission at 1030 nm is suppressed to 50 dB below the 1018 nm laser. This work shows that highly-efficient fiber laser at 1018 nm can be obtained with Yb-doped phosphosilicate fiber.

Improvement of radiation resistance by introducing CeO2 in Yb-doped silicate glasses

The influences of Ce on the radiation resistance of Yb-doped aluminosilicate glasses were investigated. The Ce ions in silicate glasses can effectively trap holes and free electrons due to their multivalency, consequently suppressing the radiation-induced absorption band. This could greatly improve the radiation resistance without obvious impact on the absorption properties of Yb-doped glasses. However, the fluorescence intensity and lifetime of Yb3+ ions were significantly decreased by high concentration Ce codoping. The mechanisms involved in these effects have also been discussed. The experiment results indicate that Yb-codoped glasses with a moderate Ce-concentration can be used as active medias for radiation–resistant materials in harsh radiation environments.

Feasibility study of Yb:YAG-derived silicate fibers with large Yb content as gain media

We present spectroscopic measurements and amplifier experiments on a new type of Yb-doped glass optical fiber derived from Yb:YAG crystal rods. The goal of this work is to provide a feasibility analysis of these novel silicate glasses as heavily-doped gain media for fiber-amplifier applications. Amplifier performance currently is limited by background losses arising from the precursor crystalline rod. Both basic spectroscopic measurements and fiber amplifier experiments, in addition to modeling efforts that include the background losses, are presented. The findings show that Yb:YAG-derived fibers are spectroscopically very similar to more conventional Yb-doped aluminosilicate materials but can be doped to considerably higher concentration, generally have greater doping and compositional uniformity, and possess advantageous stimulated Brillouin scattering (SBS) characteristics.

Photoexcitation of Yb-doped aluminosilicate fibers at 250 nm: evidence for excitation transfer from oxygen deficiency centers to Yb^3+

Emission spectra in the ~240–1100 nm wavelength region as well as the temporally resolved decay of Yb3+ and point defect spontaneous emission have been recorded when aluminosilicate optical fibers doped with Yb are irradiated with ~160 fs laser pulses having a central wavelength of ~250 nm(ℏω=5 eV). Photoexcitation of the fibers in this region of the deep ultraviolet (UV) provides access simultaneously to the Type II Si oxygen deficiency center (ODC), the non-bridging oxygen hole center (NBOHC: an oxygen-excess defect), and the Ge ODC. Emission from all of these defects in the ultraviolet and/or visible is observed, as is intense fluorescence at 976 nm from Yb3+. Absorption measurements conducted in the ~230–265 nm region with a sequence of UV light-emitting diodes reveal a continuum peaking at ~248 nm and having a spectral width of ~18 nm (FWHM), confirming that the 250 nm laser pump is photoexciting predominantly the ODC. The temporal histories of the optically active defect and rare earth ion emission waveforms, in combination with time-integrated spectra, suggest that the Si ODC(II) triplet state directly excites Yb3+ as well as at least one other intrinsic defect in the silica network. Prolonged exposure of the Yb-doped fibers to 250 nm radiation yields increased Yb3+, NBOHC, and Si ODC(II) singlet emission which is accompanied by a decline in Si ODC(II) triplet fluorescence, thus reinforcing the conclusion—drawn on the basis of luminescence decay constants—that the triplet state of Si ODC(II) is the immediate precursor to the NBOHC and is partially responsible for Yb ion emission at 976 nm. This conclusion is consistent with the observation that exposure of fiber to 5 eV radiation slightly suppresses ODC absorption in the ~240–255 nm region while simultaneously introducing an absorption continuum extending from 260 nm to below 235 nm (ℏω≈5.28 eV). These results suggest that ODC→E′ center conversion assumes a role in excitation transfer to Yb3+.

Ytterbium-doped Y 2O 3 nanoparticle silica optical fibers for high power fiber lasers with suppressed photodarkening

We report efficient laser demonstration and spectroscopic characteristics of a Yb-doped Y 2O 3 (or Y 3Al 5O 12) nanoparticle silica fiber developed by conventional fiber fabrication technique. The spectroscopy study evidences modification in the environment of Yb ions by the Y 2O 3 nanoparticles. As a result, photodarkening induced loss is reduced by 20 times relative to Yb-doped aluminosilicate fibers. The fiber is suitable for power scaling with good laser slope efficiency of 79%.

Measurement of photodarkening in Yb-doped aluminosilicate fibres at elevated temperature

Photodarkening behaviour in Yb-doped aluminosilicate fibres at elevated temperatures is reported. The fibre was core-pumped at 977 nm and the transmitted powers were monitored at 633 (probe) and 977 nm (pump) simultaneously with ∼47% of population inversion of Yb3+ ions. A saturated photodarkening loss was found, which is inversely proportional to temperature and, at ∼573 K, the loss was negligible at the pump wavelength. From the decay curves at different temperatures, it was found that the photodarkening involves second-order kinetics to form colour centres.

Reply to comment on “Photodarkening in Yb-doped aluminosilicate fibers induced by 488 nm irradiation”

In response to the Comment, we show that Engholm [Opt. Lett. 33, 1216 (2008)] misinterpret the absorption peak at 230 nm and reach mistaken conclusions that contradict their experimental results. Differences in compositions and fabrication details mean that their results are only marginally relevant to our experiments [Opt. Lett. 32, 1626 (2007)]. The excitation of electrons to a charge-transfer band around 230 nm in Yb-doped aluminosilicate glasses leads to conversion from Yb2+ to Yb3+, which, in our opinion, is more likely to account for photobleaching rather than photodarkening.

Comment on “Photodarkening in Yb-doped aluminosilicate fibers induced by 488 nm irradiation”

We present some strong evidence against the assignment of an ytterbium-related oxygen deficiency center (ODC) near 230 nm in Yb-doped aluminosilicate glass in the Letter by Yoo [Opt. Lett.32, 1626 (2007)]. The strong 230 nm absorption band is actually a charge-transfer band corresponding to the transfer of an electron from nearby oxygen ligands to the ytterbium ion and not related to ODCs.

Photodarkening in Yb-doped aluminosilicate fibers induced by 488 nm irradiation

Photodarkening of Yb-doped aluminosilicate fibers by continuous wave 488 nm irradiation was investigated. The irradiation induced significant excess loss in the UV-visible spectroscopy (VIS) region in Yb-doped aluminosilicate fibers while pure aluminosilicate fibers showed negligible induced loss. Ultraviolet-VIS-near-infrared spectroscopy revealed an absorption peak at 220 nm in unexposed Yb-doped aluminosilicate fiber preforms. The observed peak was attributed to Yb-associated oxygen deficiency centers (ODCs) and proposed as a precursor of the photodarkening. The proposed model was supported by measurements on oxygen-loaded Yb-doped aluminosilicate fibers. In these, the photodarkening could be significantly reduced, which we attribute to a smaller number of ODCs following oxygen loading.