Bismuth (Bi)-doped silica-based glasses and fibers are attractive materials for the new optical amplifiers and tunable lasers. In this paper, Bi/Al co-doped silica glass with a relatively high Bi concentration (0.552 wt.%) were prepared by using the optimized sol-gel method. Hydrofluoric acid (HF) was used as a catalyst in the reaction, which reduced the hydroxyl to lower than 5ppm in the final glass. After the process of drying and sintering, the gel was turned into the transparent glass at low temperature (~1300 °C). The optical properties of Bi/Al co-doped silica glass were also investigated. Excited by a 980 nm laser diode, broadband fluorescence centered at 1114 nm was obtained, which was ascribed to the Bi-Al active center (BAC-Al). The emission cross-section (𝜎𝑒𝑚) was calculated to be 7.4 × 10−21 cm2 for BAC-Al. In addition, ultra-broadband emission ranging from 850 nm to 1700 nm was also obtained excited by the 808 nm LD, which might be ascribed to BAC-P overlapped by other BACs. After the gaussian separation of fluorescence peak, the emission cross-section for BAC-P was 13.4×10−21 cm2. Our results confirmed the potentialities of the optimized sol-gel method in Bi-doped glass fabrication. The Bi/Al co-doped silica glass prepared in this work were promising to develop Bi-doped fibers and relative devices.
Er/Yb co-doped YAG nanopowders-derived silica fibers (YNDSFs) are fabricated from UV-curable composites and achieve 1550-nm laser generation with active fiber length of 1 cm. The UV-curable nanocomposites are consisted of 40 wt% home-made Er:YAG/Yb:YAG nanopowders and 60 wt% polymer resins. The Er:YAG/Yb:YAG nanopowders are fabricated by coprecipitation method with diameters in the range of 25 - 165 nm. An Er:YAG/Yb:YAG–polymer hybrid core rod was polymerized using high power UV-lamps, and was drawn to Er/Yb co-doped fiber in silica cladding by melting-in-tube method after debound process to remove organics. The absorption coefficients of the Er/Yb co-doped fiber were measured to be 17 dB cm-1 and 3.2 dB cm-1 at 976 nm and 1530 nm, respectively. The background loss was 0.05 dB cm-1 at 1200 nm. A linear fiber laser cavity was constructed with different length of Er/Yb co-doped fiber and a pair of FBGs (reflectivity: 99 % and 94 %) to quantify the laser performance. The maximum output powers were 7.5 mW and 1.5 mW with active fiber length of 6 cm and 1 cm, respectively. This scheme is expected to be an effective approach for obtaining Er:Yb co-doped fiber with high pump absorption for the generation of 1550-nm single-frequency fiber lasers.
A silica leakage channel microstructured optical fiber (LCMOF) is firstly drawn from a 3D printed preform. The LCMOF realized the optical signal transmission of supercontinuum spectrum from 600 nm to 1650 nm and the measured propagation loss is 15 dB/m at 632 nm and 19.5 dB/m at 1064 nm. The bending loss is 5 dB/m with 15 cm radius and 7.3 dB/m with 5 cm radius. The refractive index fluctuation is less than 7×10-4 in the fiber core region. The structure of LCMOF can be adjusted effectively by altering the pre-designed preform and optimizing drawing temperature, which result in the less defects and lower loss.
We report a new method to prepare active silica fiber preform at low temperature, not exceeding 1300℃ through the whole process. We prefabricated glass parts with nano-porous structure by UV cure equipment and debinded, the average pore diameter is about 46 nm. To prepare the active fiber preform, several different concentrations of Yb3+ ions were impregnated with solution doping method and further sintering under flowed O2. After several hours vitrification, the Yb3+- doped silica fiber preform with 0.05 wt%, 0.1 wt% and 0.2 wt% doping concentration were produced, and the size of the final fiber preform is φ3×39 mm. Then the fiber owning an Yb3+ concentration of 0.1 wt% was drawn by rod-in-tube, the measurements show that Yb3+ ions are homogeneous, central wavelength is 1030 nm, the 3 dB linewidth is about 38 nm, fluorescent lifetime is 1 ms, the fiber has absorption from Yb3+ 7 dB/m at 976 nm. To best of our knowledge, it is first time that active fiber preform is produced by this approach.
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