Fiber Core Glass Research Articles

Nanoporous glass as prospective material for fiber optics

The method of manufacturing active silica fibers by sintering nanoporous glasses has a number of advantages over methods of vapor deposition (MCVD, OVD). The features of obtaining nanoporous glasses by the method of two-phase separation of alkali borosilicate glasses are described. Examples of doping sintered nanoporous glasses with rare earth elements are given and the main results on the production of active fibers with a core are considered. It has been shown that such fibers are similar to their MCVD analogues in terms of properties. At the same time, it is possible to impregnate nanoporous glass with large (more than 1 at.%) concentration of dopants without revealing clustering effects and without noticeable fluctuations in the refractive index of the fiber core glass.

Cubic-Shaped and Rod-Shaped YPO4 Nanocrystal-Doped Optical Fibers: Implications for Next Generation of Fiber Lasers

Engineering silica optical fibers by nanoparticle doping is a promising technology that allows the introduction of new functionalities and extends their applicable fields. However, the knowledge gap about the impact of the extreme fabrication temperatures on the nanoparticle features prevents field progress. Herein, we demonstrate that the particularities of fiber fabrication, such as fast-heating rates and quenching heat treatments, can be leveraged to explore unlikely phenomena at the nanoscale under standard laboratory conditions. Tetragonal cubic-shaped and monoclinic rod-shaped YPO4 nanocrystals are in situ nucleated in a silica-based fiber core glass, slightly modified with Ge and P, which shows for the first time, the possibility of doping optical fibers with this type of nanostructures, in terms of shape, composition, and structure of the nanocrystals. Structural and anisotropic differences allow engineering differently their shape and composition in the fiber core by tailoring the drawing temperature, as revealed by a thorough study consisting of scanning electron microscopy (SEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS), and high-resolution transmission electron microscopy (HRTEM). This work demonstrates, for the first time, the possibility of doping optical fibers fabricated by modified chemical vapor deposition (MCVD) with anisotropic nanostructures, as well as the stability of the monoclinic YPO4 phase. These findings open up new avenues to study shape-dependent properties of rare-earth orthophosphate (REPO4) nanostructures in optical fibers which will allow incorporating unprecedented functionalities and will have an impact in several fields of application, such as fiber lasers and optical fiber amplifiers, among others.

Temperature Dependence of Absorption and Energy Transfer Efficiency of Er3+/Yb3+/P5+ Co-Doped Silica Fiber Core Glasses.

A high phosphorus Er3+/Yb3+ co-doped silica (EYPS) fiber core glass was prepared using the sol-gel method combined with high-temperature sintering. The absorption spectra, emission spectra, and fluorescence decay curves were measured and compared in temperatures ranging from 300 to 480 K. Compared to 915 and 97x nm, the absorption cross-section at ~940 nm (~0.173 pm2) demonstrates a weaker temperature dependence. Hence, the 940 nm pump mechanism is favorable for achieving a high-power laser output at 1.5 μm. Additionally, the double-exponential fluorescence decay of Yb3+ ions and the emission intensity ratio of I1018nm/I1534nm were measured to evaluate the energy transfer efficiency from Yb3+ ions to Er3+ ions. Through the external heating and active quantum defect heating methods, the emission intensity ratios of I1018nm/I1534nm increase by 30.6% and 709.1%, respectively, from ~300 to ~480 K. The results indicate that the temperature rises significantly reduce the efficiency of the energy transfer from the Yb3+ to the Er3+ ions.

Photodarkening-resistance improvement of Yb3+/Al3+ co-doped silica fibers fabricated via sol-gel method.

Yb3+/Al3+ co-doped silica fibers (YDFs) with almost identical core glass compositions were prepared using the sol-gel and modified chemical vapor deposition (MCVD) methods. The photodarkening (PD) and laser performance before and after the PD process were tested under 974 nm pumping. The doping homogeneity of Yb3+ ions and clusters of Yb3+ ions in preform slices of these two fibers were investigated via optical absorption spectroscopy, photoluminescence emission spectra, electron probe microanalysis (EPMA), and low-temperature (4 K) electron paramagnetic resonance (EPR). It is known that the PD resistance of YDFs prepared via the sol-gel method is significantly better than that of YDFs prepared via MCVD under the same test conditions. EPMA mapping reveals that the doping homogeneity of Yb3+ ions in the sol-gel fiber core glass is better than that in the MCVD fiber. The low-temperature (4 K) EPR and cooperative luminescence spectra of Yb3+ ions indicate that the clustering degree of Yb3+ ions in the sol-gel fiber is lower than that in the MCVD fiber. In the absorption and emission spectra, small amounts of Yb2+ ions are observed in the preform slice from the sol-gel method. A model of the color-center generation in the PD process was proposed to explain the mechanism of PD resistance improvement for the YDFs fabricated via the sol-gel method.

Preparation of Er3+/Yb3+ co‐doped citrate microstructure fiber of large mode field and its 3.0 μm laser performance

AbstractThe double‐cladding Er3+/Yb3+ co‐doped bismuth germanium gallate microstructure fiber of large mode, with the core diameter of 30.6 μm, the inner cladding air pore diameter of about 3.06 μm and a lattice constant of 10.2 μm is prepared by a bundle‐drawing method. The spectral characteristics at 975 nm wavelength were studied and the results show that the maximum fluorescence intensity and the high gain quality factor of the fiber core glass can be obtained when the molar ratio of Er3+ to Yb3+ is 0.5%:2% and its emission cross section is up to 10.9 × 10−21 cm2. A stable laser output with a maximum power of 51.16 mW and a wavelength of 2710 nm was obtained in a microstructure optical fiber with a length of 160 mm employing a independently constructed fiber laser with a cascade structure, whose pump light power was 561 mW, the slope efficiency was 6.89%, the effective mode field area is about 576 μm2 and the beam quality factor M2 < 1.02. The double‐cladding Er3+/Yb3+ co‐doped bismuth germanium gallate microstructure fiber of large mode has excellent laser properties and is an ideal optical fiber material for the development of the 3.0 μm laser.

Effect of electron irradiation on the optical properties of bismuth doped hafnia-yttria-alumina-silicate fiber

We report a study on transformations in absorption and emission spectra of novel bismuth (Bi) doped hafnia-yttria-alumina-silicate fiber, which arise as the result of bombardment by high-energy (β) electrons. Among the featuring data obtained, we reveal substantial growth of ‘active’ Bi center content in the fiber core-glass with increasing β-irradiation dosage, resulting in dose-dependent intensification of the resonant-absorption bands and enhancement of the emissive potential of the fiber in near-IR, inherent to these centers.

Bismuth‐Doped Multicomponent Optical Fiber Fabricated by Melt‐in‐Tube Method

Bismuth‐doped multicomponent optical fiber was fabricated by a melt‐in‐tube method. The fiber was prepared at drawing temperature where the clad was softened, while the fiber core glass was melted. The obtained fiber was characterized by electroprobe microanalyzer and X‐ray diffraction. No obvious precipitation of crystals or bismuth metals was observed in the fiber. Excited by 808‐nm laser, intense broadband near‐infrared emission with full width at half maximum of about 325 nm was observed from the fiber. Consequently, this fiber is promising for broadband fiber amplification. The melt‐in‐tube method is generally applicable for fabricating bismuth‐doped multicomponent optical fiber.

Spectroscopic and laser properties of Al-P co-doped Yb silica fiber core-glass rod and large mode area fiber prepared by sol-gel method

A large-size (∅5 mm) Yb3+-doped silica fiber core-glass rod with an Al-P co-doped composition: 0.035Yb2O3-1.0Al2O3-1.0P2O5-97.965SiO2 (mol%) was prepared by the sol-gel method combined with high-temperature melting technology. We successfully solved the doping homogeneity problem caused by the volatility of P2O5. The doping homogeneity of the glass rod was very high with the maximum refractive index fluctuation Δn < 2 × 10−4. The refractive index of the glass rod was very low because of the equimolar amounts of Al and P co-doping, which yielded an AlPO4 structure. A large-mode-area single cladding fiber (LMA SCF) and photonic crystal fiber (LMA PCF) with core diameters of 35 and 50 µm, respectively, were drawn from this glass rod. Owing to the low refractive index of the core-glass rod and the corresponding low numerical aperture (NA, 0.033) of the core, the LMA SCF exhibited a high laser beam brightness with M2 = 1.3-1.4. The LMA PCF exhibited the maximum output power, which was limited by the available pumping power, of 46 W and the slope efficiency of 61%.

Ni(2+) doped glass ceramic fiber fabricated by melt-in-tube method and successive heat treatment.

Glass ceramic fibers containing Ni(2+) doped LiGa(5)O(8) nanocrystals were fabricated by a melt-in-tube method and successive heat treatment. Fiber precursors were prepared by drawing at high temperature where fiber core glass was melted while fiber clad glass was softened. After heat treatment, LiGa(5)O(8) nanocrystals were precipitated in the fiber core. Excited by 980 nm laser, efficient broadband near-infrared emission was observed in the glass ceramic fiber compared to that of precursor fiber. The melt-in-tube method can realize controllable crystallization and is suitable for fabrication of novel glass ceramic fibers. The Ni(2+)-doped glass ceramic fiber is promising for broadband optical amplification.

Fabrication and Characterization of Glass‐Ceramic Fiber‐Containing Cr3 + ‐Doped ZnAl2O4 Nanocrystals

Glass‐ceramic fibers containing Cr3+‐doped ZnAl2O4 nanocrystals were fabricated by the melt‐in‐tube method and successive heat treatment. The obtained fibers were characterized by electro‐probe micro‐analyzer, X‐ray diffraction, Raman spectrum and high‐resolution transmission electron microscopy. In our process, fibers were precursor at the drawing temperature where the fiber core glass was melted while the clad was softened. No obvious element interdiffusion between the core and the clad section or crystallization was observed in precursor fiber. After heat treatment, ZnAl2O4 nanocrystals with diameters ranging from 1.0 to 6.3 nm were precipitated in the fiber core. In comparison to precursor fiber, the glass‐ceramic fiber exhibits broadband emission from Cr3+ when excited at 532 nm, making Cr3+‐doped glass‐ceramic fiber a promising material for broadband tunable fiber laser. Furthermore, the melt‐in‐tube method demonstrated here may open a new gate toward the fabrication of novel glass‐ceramic fibers.

Short-length fiber laser oscillation in 4-mm Nd-doped silica fiber fabricated by zeolite method

We demonstrated laser oscillation in an only 4-mm Nd-doped silica fiber, which is 10 times shorter than the previously reported one. This fiber-core glass, which was fabricated by the zeolite method, contained 1.25wt% of Nd2O3. The laser output power was observed to be 3.1mW at 1060nm, and the laser threshold power and slope efficiency were 7.7mW and 8.9%, respectively. Nd-doped silica fiber can produce high-repetition and extremely compact short-pulse laser devices and will also be applied to optical integrated circuits with environmental toughness in practical use.

Laser oscillation in 5-cm Nd-doped silica fiber fabricated by zeolite method

We have demonstrated a laser oscillation in the highest concentration and the shortest Nd-doped silica fiber, an only 5-cm multimode Nd-doped silica fiber. This fiber-core glass was fabricated by the zeolite method, and the glass contained 1.25 wt.% of Nd 2O 3, which is 10 times higher than previously reported Nd-doped silica fiber. The laser output power was 10 mW at 1062 nm, and the threshold power and slope efficiency of the laser oscillation was 1.39 W and 2.4%, respectively.

Three-cascaded 1407-nm Raman laser based on phosphorus-doped silica fiber

We report a laser-diode-pumped 1407-nm Raman fiber laser with an output power of 1 W. In this three-cascaded cw Raman laser, based on a single active phosphorus-doped silica fiber, for the first time to the authors' knowledge successive generation of Stokes components of essentially different frequency shifts (1330 and 490cm(-1)) has been realized. These Stokes components are associated with both constituents (P(2)O(5) and SiO(2)) of the fiber core glass.