Search Results (21)

Bi-doped glasses and fibers have been widely applied in solid-state and fiber lasers. However, the mechanism underlying near-infrared (NIR) luminescence remains unclear, and Bi-related luminescence centers (BLCs) are prone to alteration during fiber fabrication, making it challenging to achieve high-performance Bi-doped glass fibers. In this work, Bi-, Bi-Al-, and Bi-Ge-doped silica glasses were investigated to elucidate the origin of NIR luminescence. Two broad NIR fluorescence bands were observed in silica glasses, originating from distinct BLCs. The longer-wavelength fluorescence band at 1423 nm, demonstrating sensitivity to Bi doping concentration and homogeneity, is attributed to Bi clusters (aggregates of Bi⁺ ions), whereas the shorter-wavelength emission, independent of Bi concentration, originates from isolated Bi⁺ ions. A vacuum-assisted melting-in-tube method with a single-step heating process was employed to fabricate Bi-doped silica-based glasses and fibers. The fluorescence bands of the fibers remained consistent with those of the precursor glasses, indicating no new BLCs were formed during fiber fabrication. The modulation of fluorescence bands was primarily governed by Bi cluster formation. Suppressing Bi clustering through co-doping with Al/Ge or optimizing fabrication conditions offers an effective route to tailor the fluorescence properties of Bi-doped glasses and fibers. Full article

Using electrospun nanofibers doped with TiO₂ and rare-earth ion Ho³+ as the matrix, and sodium gluconate as the reducing agent, Bi(NO₃)₃ was reduced using hydrothermal technology to produce Bi@Ho³⁺:TiO₂ composite fiber materials. The materials’ phase, morphology, and photoelectric properties were characterized using various analytical testing methods, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), and transient photocurrent (IP). During the hydrothermal process, it was confirmed that Bi³⁺ was reduced by sodium gluconate to form pure Bi nanoparticles, which combined with Ho³⁺:TiO₂ nanofibers to form heterojunctions. By leveraging the surface plasmon resonance (SPR) effect of metallic Bi and the abundant energy level structure and 4f electron transition properties of rare-earth Ho³⁺, the TiO₂ nanofibers underwent dual modification, effectively enhancing the photocatalytic activity and stability of TiO₂. Under visible light irradiation, the rate of hydrogen production through water decomposition reached 43.6 μmol·g⁻¹·h⁻¹. Full article

A series of glasses based on (80-y) TeO₂-20 BiCl₃-y RE₂O₃ (y = 0, 0.6 mol%; RE = Nd, Sm, Dy, and Er) were prepared. The thermal stability of the glass was determined by differential scanning calorimetry (DSC). The density and optical energy values of the prepared glass increased in the order of Sm₂O₃, Nd₂O₃, Dy₂O₃, and Er₂O₃. In addition, the glass doped with Er₂O₃ had the highest refractive index values compared to the other samples. Subsequently, Judd–Ofelt parameters (Ω₂, Ω₄, and Ω₆) were obtained for the family of RE³⁺ trivalent rare-earth ions introduced as dopants in a tellurite glass. These parameters were calculated from the absorption spectra for each RE³⁺. The structures were studied by Raman spectroscopy deconvolution, which determined that TeO₄, TeO₃, TeO₃₊₁, BiO₆, and BiCl₆ units had formed. In addition, the structural changes in the glass are related to the intensity ratio of TeO₄/TeO₃, depending on the type of rare-earth. For the optics and Judd–Ofelt parameters, the ray spectroscopy results of the prepared glass show that it is a good candidate for nonlinear optics fibers, a solid laser material. Full article

Limited by stimulated Raman scattering (SRS), amplified spontaneous emission (ASE) and transverse mode instability (TMI), it is challenging to achieve high-power laser output in ytterbium-doped fiber (YDF) lasers with operating wavelengths less than 1060 nm. In high-power fiber lasers, bi-tapered YDF can provide a balance between the suppression of SRS and TMI. In this work, we designed and fabricated a new double-cladding asymmetric bi-tapered YDF to suppress ASE and SRS in the 1050 nm monolithic fiber laser. The asymmetric bi-tapered YDF has an input end with a core/cladding diameter of ~20/400 μm, a middle section with a core/cladding diameter of ~30/600 μm and an output end with a core/cladding diameter of ~25/500 μm. The working temperature of the non-wavelength-stabilized 976 nm laser diodes was optimized to improve the TMI threshold. An output power of over 5 kW with an efficiency of 83.1% and a beam quality factor M² of about 1.47 were achieved. To the best of our knowledge, this represents the highest power nearly-single mode in 1050 nm fiber lasers. This work demonstrates the potential of asymmetric bi-tapered YDF for achieving a high-power laser with high beam quality in 1050 nm fiber lasers. Full article

In recent years, great progress has been made in the technology of high-purity and ultra-dry tellurite glasses, which has enabled the creation of high-purity single-mode tellurite fibers doped with rare-earth ions. This technology has made it possible to demonstrate laser generation in the range of about 2.7 μm in erbium-doped tungsten tellurite fibers. In this paper, we present an experimental study of broadband amplification in erbium-doped zinc-tellurite fibers. Zinc-tellurite glasses containing modifying components, such as Na₂O, La₂O₃, Bi₂O₃, or rare-earth metal oxides, are known to have noticeably lower phonon energy than heavy metal-tellurite systems, namely, tungsten tellurite glasses, which leads to better lasing output. The on-off gain of 30- and 60-cm long zinc-tellurite fibers has been measured in a wide range of diode pump powers. It has been shown for the first time that the amplification band is essentially extended, with pump power reaching over 250 nm (2600–2850 nm) at a peak power of about 40 W for a 30-cm long fiber. Full article

The polarization properties of bismuth active centers (BACs) are important for many applications of bismuth-doped fibers, but they are still lacking in study. In this paper, we present the measurements of polarized luminescence (PL) of the BACs formed in a Bi-doped phosphosilicate glass matrix. This research was performed on phosphosilicate fiber preforms used for the drawing of active bismuth-doped fibers for efficient optical amplifiers and lasers. The degree of polarization (DOP) of luminescence of the BACs associated with phosphorus and silica (BAC-P and BAC-Si) is provided and discussed. The DOP of luminescence at the 1320 nm wavelength appeared to be around 19%, 0% and 7.5% for pumps at 1240 nm, 762 nm and 425 nm, respectively. The DOP of PL caused by resonant excitation may be described in terms of a model of a partially anisotropic oscillator with the parameters represented by the principal axes of an ellipsoid. For the resonant excitation at 1240 nm, the ratio of the major principal axis to the minor one turned out to be 5.1 and 3.0 for BAC-P and BAC-Si, respectively. Full article

For the first time, polysulfones (PSFs) were synthesized with chlorine and hydroxyl terminal groups and studied for the task of producing porous hollow fiber membranes. The synthesis was carried out in dimethylacetamide (DMAc) at various excesses of 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A) and 4,4′-dichlorodiphenylsulfone, as well as at an equimolar ratio of monomers in various aprotic solvents. The synthesized polymers were studied by nuclear magnetic resonance (NMR), differential scanning calorimetry, gel permeation chromatography (GPC), and the coagulation values of 2 wt.% PSF polymer solutions in N-methyl-2-pyrollidone were determined. According to GPC data, PSFs were obtained in a wide range of molecular weights M_w from 22 to 128 kg/mol. NMR analysis confirmed the presence of terminal groups of a certain type in accordance with the use of the corresponding monomer excess in the synthesis process. Based on the obtained results on the dynamic viscosity of dope solutions, promising samples of the synthesized PSF were selected to produce porous hollow fiber membranes. The selected polymers had predominantly –OH terminal groups and their molecular weight was in the range of 55–79 kg/mol. It was found that porous hollow fiber membrane from PSF with M_w 65 kg/mol (synthesized in DMAc with an excess of Bisphenol A 1%) has a high helium permeability of 45 m³/m²∙h∙bar and selectivity α (He/N₂) = 2.3. This membrane is a good candidate to be used as a porous support for thin-film composite hollow fiber membrane fabrication. Full article

Polyvinylidene fluoride (PVDF) dual-layer hollow fiber membranes were simultaneously fabricated by thermally induced phase separation (TIPS) and non-solvent induced phase separation (NIPS) methods using a triple orifice spinneret (TOS) for water treatment application. The support layer was prepared from a TIPS dope solution, which was composed of PVDF, gamma-butyrolactone (GBL), and N-methyl-2-pyrrolidone (NMP). The coating layer was prepared from a NIPS dope solution, which was composed of PVDF, N,N-dimethylacetamide (DMAc), and polyvinylpyrrolidone (PVP). In order to improve the mechanical strength of the dual-layer hollow fiber, a nucleating agent, sodium 2,2′-methylene bis-(4,6-di-tert-butylphenyl) phosphate (NA11), was added to the TIPS dope solution. The performance of the membrane was evaluated by surface and cross-sectional morphology, water flux, mechanical strength, and thermal property. Our results demonstrate that NA11 improved the mechanical strength of the PVDF dual-layer hollow fiber membranes by up to 42%. In addition, the thickness of the coating layer affected the porosity of the membrane and mechanical performance to have high durability in enduring harsh processing conditions. Full article

In this paper, we study the implementation of a secure key distribution system based on an ultra-long fiber laser with a bi-directional erbium-doped fiber amplifier. The resilience of the system was tested against passive attacks from an eavesdropper. A similarity was observed in the spectra for both secure configurations of the system and no signature that would allow an eavesdropper to obtain the secure state of the system was observed during the state transitions. Full article

In this paper, we report the latest research results on the fabrication of double-clad Bi-doped germanosilicate core fibers with a rectangular inner cladding design for improved laser performance in the near-IR spectral region. Detailed comparative analysis of the absorption characteristics of the Bi-doped fibers with a circular- and rectangular-shaped inner cladding was performed. A series of cladding-pumped, Bi-doped fiber lasers emitting near 1.46 µm was developed using the semiconductor’s multi-mode fiber-coupled laser diodes at $\lambda$ = 808 nm. The peculiarities of the laser parameters of the fabricated active fibers with the double-clad design were thoroughly studied by analyzing the dependencies of the slope efficiency of the lasers, namely the pump power, active fiber length and core-to-inner-cladding area ratio. The obtained results show that the rectangular design provided enhanced cladding absorption and improvements in laser performance. In particular, we achieved maximal slope efficiencies of 5.5% and 4.3% for the absorbed pump power introduced into the inner cladding with cross-section areas of 80 × 80 µm${}^2$ and 125 × 125 µm${}^2$, respectively. Multi-wavelength lasing operation in a free-running cavity due to a few modes’ propagation regimes was found using the Bi-doped fiber with an 80 × 80 µm${}^2$ inner cladding. Full article

A novel series of glass, consisting of B₂O₃, Bi₂O₃, TeO₂, and TiO₂ (BBTT) containing rare earth oxide RE₂O₃, where RE is La, Ce, Sm, Er, and Yb, was prepared. We investigated the structural, optical, and gamma attenuation properties of the resultant glass. The optical energy bands, the linear refractive indices, the molar refractions, the metallization criteria, and the optical basicity were all determined for the prepared glass. Furthermore, physical parameters such as the density, the molar volume, the oxygen molar volume, and the oxygen packing density of the prepared glass, were computed. Both the values of density and optical energy of the prepared glass increased in the order of La₂O₃, Ce₂O₃, Sm₂O₃, Er₂O₃, and then Yb₂O₃. In addition, the glass doped with Yb₂O₃ had the lowest refractive index, electronic polarizability, and optical basicity values compared with the other prepared glass. The structures of the prepared glass were investigated by the deconvolution of infrared spectroscopy, which determined that TeO₄, TeO₃, BO₄, BO₃, BiO₆, and TiO₄ units had formed. Furthermore, the structural changes in glass are related to the ratio of the intensity of TeO₄/TeO₃, depending on the type of rare earth. It is also clarified that the resultant glass samples are good attenuators against low-energy radiation, especially those that modified by Yb₂O₃, which exhibited superior shielding efficiency at energies of 622, 1170, and 1330 keV. The optical and gamma ray spectroscopy results of the prepared glass show that it is a good candidate for nonlinear optical fibers, laser solid material, and optical shielding protection. Full article

The Bi/Sn-doped aluminosilicate glass samples were prepared using a melting–quenching method and their near-infrared (NIR) emission properties were studied. An ultra-broadband NIR emission ranging from 950 nm to 1600 nm was observed in all samples under 480 nm excitation, which covered the whole fiber low-loss window. The NIR emission spectrum showed that the maximum emission peak was about 1206 nm and the full width at half maximum (FWHM) was about 220 nm. Furthermore, the NIR emission intensity strongly depends on the composition of the glass, which can be optimized by modulating the glass composition. The Bi⁰ and Bi⁺ ions were the NIR luminescence source of the glass samples in this paper. The Bi/Sn-doped aluminosilicate glass has the potential to become a new type of core fiber material and to be applied to optical fiber amplifiers (OFAs), based on its excellent performance in ultra-broadband NIR emission. Full article

Fiber lasers have long remained relevant for various applications worldwide in many industries. This paper presents a mode-locked ytterbium-doped fiber laser (YDFL) using our home-made topological insulator Bi₂Se₃ nanosheets (TI Bi₂Se₃) as the saturable absorber. The fabricated TI Bi₂Se₃ is transported to the end of the fiber ferrule using an optical deposition process, which is a key ingredient for initiating a pulsed fiber laser. With a pump power of 211.1 mW, the captured repetition rate and pulse width are 8.3 MHz and 6.2 ns, respectively. The length of the setup configuration is approximately 20 m, which corresponds to an output power measurement of 12.4 mW with a calculated pulse energy of 1.5 nJ. There are no significant Kelly sidebands, but the strong stability of the pulsed laser is defined by a high signal-to-noise ratio (SNR) of around 60.35 dB. Full article

A visible-light-Fenton-like reaction system was constructed for the selective conversion of peroxymonosulfate to sulfate radical. Au@CoS, when doped on monoclinic BiVO₄ {010} facets, promoted spatial charge separation due to the different energy band between the m-BiVO₄ {010} and {110} facets. The visible-light response of m-BiVO₄ was enhanced, which was attributed to the SPR effect of Au. And the photogenerated electrons were transferred from the m-BiVO₄ {010} facet to Au via a Schottky junction. Owing to higher work function, CoS was able to capture these photoelectrons with acceleration of the Co(Ⅱ)/Co(Ⅲ) redox, enhancing peroxymonosulfate conversion to sulfate radical (Co²⁺ + HSO₅⁻→ Co³⁺ + •SO₄⁻ + OH⁻). On the other hand, holes accumulated on m-BiVO₄ {110} facets also contributed to organics oxidation. Thus, more than 95% of RhB was degraded within 40 min, and, even after five cycles, over 80% of RhB could be removed. The radical trapping experiments and EPR confirmed that both the sulfate radical and photogenerated hole were the main species for organics degradation. UV-vis DRS, photoluminescence (PL) and photoelectrochemical analyses also confirmed the enhancement of the visible-light response and charge separation. In a pilot scale experiment (PMS = 3 mM, initial TOC = 151 mg/L, reaction time = 4 h), CoS-Au-BiVO₄ loaded on glass fiber showed a high mineralization rate (>60%) of practical wastewater. Full article