BaF2 LaF3 AlF3 NaF Research Articles

A quantitative characterization of micro-gravity and unit-gravity processed ZBLAN glass

Micro-gravity processing has been proven to suppress crystallization in ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) glass. Crystallization suppression and characterization is the next step towards the development of low-loss mid-Infrared (IR) fiber optics. This study focuses on the characterization of micro-gravity versus unit-gravity processed ZBLAN glass. A unique quantitative crystallization characterization technique was employed on the samples that utilize a combination of Differential Interference Contrast (DIC) optical microscopy with on board microscope counting and measuring software techniques. To date, past researchers who have studied the crystallization suppression of ZBLAN glass in micro-gravity have only characterized their material through visual inspection of micrographs. This study makes use of optical micrographs while providing additional quantitative data that has been lacking from previous studies. This novel characterization technique provides additional insight into understanding the crystallization behavior of ZBLAN glass that can lead to the development of low-loss mid IR fiber optics. The results from this study show that the quantification data agrees with the micrographs, however, the new results show a more precise degree of crystallization suppression through quantified data, such as crystallite size and amount per sample.

The Effect of Microcrystals on ZrF4-BaF2-LaF3-AlF3-NaF Glass Fiber Fracture

The mechanical response of materials to an applied force is determined by the inherent microstructure properties of the material.Microcrystals formed during heating and fiber drawing represent inherent flaws, which play a strong role in the mechanical properties as well as the handling ability of optical waveguides, in particular ZBLAN (ZrF4–BaF2–LaF3–AlF3–NaF) fibers. The property of the fiber to flex and bend is useful for handling and positioning the fiber in a desired application. A series of ZBLAN fibers were bent to specific radii of curvature to determine the applied curvature at which fiber fracture occurs. The fibers were first subjected to a tailored temperature arrangement for a designated amount of time to induce varying amounts of crystal formation. The fiber failure was documented and photographed with the aid of optical microscopy and scanning electron microscopy. Fracture mechanics analysis was used to characterize the impact of crystal size on the failure of the ZBLAN fiber. The results of this assessment show the impact of thermal degradation on ZBLAN fibers as well as suggest an optimum fiber drawing take-up reel diameter.

Rare-earth doped colour tuneable up-conversion ZBLAN phosphor for enhancing photocatalysis

Rare-earth doped ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) fluoride glasses have been successfully synthesized showing outstanding UV–VIS up-conversion luminescence of Er3+ and Tm3+, sensitized by Yb3+ ions, under near-infrared excitation at 980nm. The ratio between blue, green and red up-conversion emission bands can be adjusted by varying the pump power density of the incident infrared radiation, resulting in a controlled tuneability of the overall emitting colour from greenish to yellowish. Additionally, the observed high energy UV intense up-conversion emissions are suitable to enhance photocatalytic activity of main water-splitting semiconductor electrodes (such as TiO2) used in sustainable production of hydrogen. Photocatalysis and photolysis degradation of methylene blue in water under sun-like irradiation using benchmark photocatalyst (TiO2 Degussa P25) have been boosted by 20% and by a factor of 2.5 respectively, due to the enhancement of UV radiation that reaches the TiO2 particles by the addition of ZBLAN powder into a slurry-type photo-reactor. Hence, up-conversion ZBLAN phosphors contribute to demonstrate the possibility of transforming the incoming infrared radiation into the UV region needed to bridge the gap of photocatalytic semiconductors.

White emission from Tm3+/Tb3+/Eu3+ co-doped fluoride zirconate under ultraviolet excitation

We synthesize Tm3+/Tb3+/Eu3+ triply-doped ZrF4—BaF2—LaF3—AlF3—NaF (ZBLAN) transparent glass by using a melt-quenching method. Under excitation of 365 nm, the white emission with Commission internationale deL'Eclairage (CIE) coordinates of (0.33, 0.33) is achieved at the Eu3+ concentration of 1.1 mol%. The mechanisms for white emission and the energy transfer process of Tb3+ → Eu3+ are discussed in terms of the photoluminescence, photoluminescence excitation spectra, and the light emission decay curves. The nature for the Tb3+ → Eu3+ energy transfer is described with the aid of an energy level diagram.

Enhanced refractive index without absorption in optical fibers via an indirect incoherent pump field

We demonstrate a scheme for realizing the refractive index with zero absorption in an Er3+-doped ZrF4–BaF2–LaF3–AlF3–NaF optical fiber. It is found that the refraction index of the probe laser can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optical-fiber communication.

Understanding the role of gravity in the crystallization suppression of ZBLAN glass

ZBLAN (ZrF4–BaF2–LaF3–AlF3–NaF) glass fibers are excellent materials for the use in many applications, such as fiber optics, fiber amplifiers, and lasers for cutting, drilling, and surgery. The main advantage of ZBLAN glasses over other glasses, such as silica, is its superior infrared transmissibility. The theoretical optical transmission spectrum for a ZBLAN fiber is from 0.3 μm in the UV to 7 μm in the IR region. The main obstacle with ZBLAN glass is the extrinsic losses from impurities, which includes crystallites formed during the manufacturing process. Due to ZBLAN’s narrow working range, crystallites easily form during the drawing process, which inhibits the materials transmissibility. Microgravity (μ-g) processing has been proven to suppress crystallization in ZBLAN glass, thus allowing the material to reach its theoretical loss coefficient. Past researchers have shown that this phenomenon exists, but the mechanism of crystallization suppression in a microgravity environment is not well understood. This research endeavors to understand the role that gravity plays on the crystallization suppression of ZBLAN glass. The outcome of this study will impact the production of superior mid-IR fiber optics and could lead to a more feasible manufacturing technique. The main conclusion developed from this study is that the process is heavily dependent upon mass transfer kinetics such as diffusion and buoyancy-driven convection. Thus, suppressing buoyancy-driven convection, at relevant drawing temperatures, suppresses crystallization growth in ZBLAN glass. This theory was proven through microgravity experimentation, analytical, and computational modeling.

Large refractive index with vanishing absorption in optical fibers

We propose and demonstrate a novel scheme for realizing large refractive index with vanishing absorption in a three-level quantum system consisting of the energy levels of Er3+-doped ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) optical fiber. It is found that the refractive index of the probe field can be controlled via the coherent coupling field and incoherent pumping field. The switching from negative refractive index to positive refractive index and manipulation of the value of the index of refraction while maintaining vanishing absorption of the probe field can be achieved via tuning the detuning of the coherent coupling field. Our scheme may provide some new possibility for technological applications in fiber communication.

A novel 2-μm pulsed fiber laser based on a supercontinuum source and its application to mid-infrared supercontinuum generation

A new method to achieve 2-μm pulsed fiber lasers based on a supercontinuum (SC) is demonstrated. The incident pump light is a pulsed SC which contains a pump light and a signal light at the same time. The initial signal of the seed laser is provided by the incident pump light and amplified in the cavity. Based on this, we obtain a 2-μm pulsed laser with pulse repetition rate of 50 kHz and pulse width of 2 ns from the Tm-doped fiber laser. This 2-μm pulsed laser is amplified by two stages of fiber amplifiers, then the amplified laser is used for mid-infrared (mid-IR) SC generation in a 10-m length of ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) fiber. An all-fiber-integrated mid-IR SC with spectrum ranging from 1.8 μm to 4.3 μm is achieved. The maximal average output power of the mid-IR SC from the ZBLAN fiber is 1.24 W (average output power beyond 2.5 μm is 340 mW), corresponding to an output efficiency of 6.6% with respect to the 790-nm pump power.

Heavy rare-earth-doped ZBLAN glasses for UV–blue up-conversion and white light generation

Noticeable UV–vis up-conversion luminescence of Er3+ and Tm3+ ions sensitised by Yb3+ ions in ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) fluoride glasses have been obtained under near-infrared excitation at 980nm. Red, green and blue simultaneous emissions were observed yielding to a white-balanced overall colour. Moreover significant UV up-conversion emissions observed can contribute to enhance spectral response of semiconductor electrode, such as TiO2 and Fe2O3, for sustainable production of hydrogen via water photolysis by harvesting of long wavelength solar irradiation, emerging as an interesting solely luminescent approach for improving water-splitting. Total infrared to UV–vis up-conversion efficiency has been calculated to be at around 46%. Laboratory tests prove the improvement in the photocatalytic action of a commercial benchmark photocatalyst (TiO2 Degussa P25) in the decomposition of methylene blue in water under sun-like irradiation, by a factor of 16% driven by up-conversion effects due to the inclusion of RE-doped ZBLAN powders into a slurry-type photo-reactor.

Enhancement of Kerr nonlinearity at λ = 1550 nm in an Er3+-doped optical fiber

The Kerr nonlinearity behavior in an Er3+-doped ZrF4–BaF2–LaF3–AlF3–NaF optical fiber is investigated theoretically. It is found that by increasing the intensity of the coherent coupling field and in the presence of an incoherent pumping field, the enhanced Kerr nonlinearity with reduced absorption can be achieved at long wavelength, i.e. λ = 1550 nm, which is practical for communicational applications. In addition, it is found that the rate of incoherent pump field can significantly decrease the maximal Kerr nonlinearity of the medium. The impact of frequency detuning of the coherent field on linear and nonlinear susceptibilities is discussed.

High refractive index without absorption in a rare-earth-ion-doped optical fiber

We demonstrate a new scheme for realizing the high refractive index with zero absorption in an Er3+-doped ZrF4–BaF2–LaF3–AlF3–NaF optical fiber. It is found that the refraction index of the probe laser can easily be controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optical-fiber communication.

Controllable optical bistability and multistability in a rare-earth-ion-doped optical fiber

We investigated the optical bistability and multistability in an Er3+-doped ZrF4–BaF2–LaF3–AlF3–NaF optical fiber inside an optical ring cavity. It is found that the optical bistability and multistability can be easily controlled via adjusting properly the parameters of the corresponding system. Our scheme may provide some new possibilities for technological applications in optoelectronics and optical-fiber communication.

Preparation and Characterization of High‐Purity Metal Fluorides for Photonic Applications

We combine chelate‐assisted solvent extraction (CASE) and hot hydrogen fluoride gas treatment to enable a general method for the preparation of high‐purity binary metal fluorides. The fluorozirconate glass ZBLANI:Yb3+ (ZrF4–BaF2–LaF3–AlF3–NaF–InF3–YbF3), a solid‐state laser‐cooling material, is used as a test case to quantitatively assess the effectiveness of the purification method. The reduction of transition‐metal and oxygen‐based impurities is quantified directly by inductively coupled plasma mass spectrometry (ICP‐MS) and indirectly by laser‐induced cooling, respectively. The concentrations of Cu, Fe, Co, Ni, V, Cr, Mn, and Zn impurities in the ZrCl2O precursor solution were measured individually by ICP‐MS at various stages of the purification process. CASE was found to reduce the total transition‐metal concentration from 72500 to ~100 ppb. Laser cooling was most efficient in ZBLANI:Yb3+ glass fabricated from CASE‐purified metal fluoride precursors, confirming the results of the ICP‐MS analysis and demonstrating the effectiveness of the purification methods in a finished optical material. High‐purity metal fluorides prepared by the methods presented herein will enable new high‐performance optical materials for solid‐state optical refrigerators, crystals for vacuum ultraviolet (VUV) spectroscopy of the Thorium‐229 nucleus, VUV optics, fibers, and thin‐film coatings.

Ultralow threshold green lasing and optical bistability in ZBNA (ZrF4–BaF2–NaF–AlF3) microspheres

Upconversion lasing and fluorescence from active microspheres fabricated from a novel fluorozirconate, Er3+ doped glass, ZBNA (ZrF4–BaF2–NaF–AlF3), when pumped at 978 nm via a tapered optical fiber is demonstrated. An ultralow, green lasing threshold of ∼3 μW for 550 nm emissions is measured. This is one order of magnitude lower than that previously reported for ZBLAN (ZrF4–BaF2–LaF3–AlF3–NaF) microspheres. Optical bistability effects in ZBNA microspheres are reported and the bistable mechanism is discussed and attributed to shifts of the whispering gallery modes due to thermal expansion of the sphere, where heating is achieved by optical pumping around 978 nm. The effect of the bistability on the upconversion lasing is examined and we report multiple bistability loops within the microspheres.

Self-fabricated single mode waveguide in fluoride glass excited by self-channeled plasma filaments

Self-fabricated permanent structure of single mode waveguide in optical fluoride glasses was demonstrated using the self-channeled plasma filament excited by a femtosecond (130fs) Ti:sapphire laser (λp=790nm). The photoinduced refractive index modification in ZrF4–BaF2–LaF3–AlF3–NaF glasses reached a length of approximately 10–15mm from the input surface of the optical glass with the diameters ranging from 5to8μm at the input intensities of more than 1.0×1012W∕cm2. The graded refractive index profiles were fabricated to be a symmetric form from the center of optical fluoride glass, and a maximum value of refractive index change (Δn) was measured to be 1.3×10−2. The beam profile of the output beam transmitted through the modified region showed that the photoinduced refractive index modification produced a permanent structure of single mode waveguide.

The effects of a magnetic field on the crystallization of a fluorozirconate glass

An axial magnetic field of 0.1 T was applied to ZrF4–BaF2–LaF3–AlF3NaF fibers during heating to the glass crystallization temperature. Scanning electron microscopy and x-ray diffraction were used to identify crystal phases. It was shown that fibers exposed to the magnetic field did not crystallize, while fibers not exposed to the field did crystallize. A hypothesis based on magnetic work was proposed to explain the results, and was tested by measuring the magnetic susceptibilities of the glass and crystal.

Broadband and High Efficient 1530 nm Emission from OxyfluorideGlass Ceramics Codoped with Er3+ and Yb3+ Ions

The emission at 1530 nm and its applications in optical communicationsare discussed. The efficient width of the emission band Δeff,which is up to 91 nm, is larger as compared with silica-based glass,bismuth glass and ZrF4–BaF2–LaF3–AlF3–NaF(ZBLAN) glass doped by Er3+ ions. Under the excitation of 785 nmlaser, the emission integral intensity of 1530 nm increases about fivetimes in the glass ceramics higher than that in the glass. This isexplained by the quantum cutting process by two-photon emission withphonon assistance. The results indicate that the glass ceramics are apromising candidate for developing broadband optical amplifiers inwavelength-division multiplexed systems.

Feasibility evaluation of intracavity solid state laser cooling to cryogenic temperatures

The requirements for obtaining cryogenic temperatures (i.e. 150 K and below) by anti-Stokes fluorescence cooling are analysed for a dielectric cooling medium located inside the cavity of a diode-pumped solid state laser. The cooling efficiency is derived in terms of pump beam parameters, intracavity loss associated with the cooling medium, reabsorption and saturation effects in the gain medium, radiative and conductive heat load on the cooling medium, and finally bulk and surface heating effects. Using experimental data for a Yb3+:ZrF4–BaF2–LaF3–AlF3–NaF [ZBLAN] cooling medium and a Yb3+:KY(WO4)2 [KYW] gain medium, the conditions for optimum cooling efficiency are obtained. Based on realistic materials properties, the analysis shows that it is feasible to obtain a cooling efficiency (i.e. cooling power per input diode pump power) of approximately 0.1% at an operating temperature of 150 K, with a heat lift up to 30 mW.

Blue Up-Conversion Fibre Laser Pumped by a 1120-nm Raman Fibre Laser

A Tm3+-doped ZrF4–BaF2–LaF3–AlF3–NaF(ZBLAN) fibre up-conversion laser pumped by a 1120-nm Raman fibre laseris demonstrated with blue output power levels up to 116 mW. For theoutput mirror with 80% reflectivity, the slope efficiency is about15%, the optical-to-optical conversion efficiency is 11%, and themaximum un-saturated output power is 116 mW. For 60% reflectivity, theslope efficiency is about 18% and the optical-to-optical conversionefficiency is 12%, whilst the maximum saturated output power is about80 mW due to the existence of photo-degradation effect in Tm3+doped ZBLAN glass fibre.

784-nm amplified spontaneous emission from Tm^3+-doped fluoride glass fiber pumped by an 1120-nm fiber laser

We report 784-nm (1G4 --> 3H5 transition) amplified spontaneous emission (ASE) from Tm3+-doped fluoride (ZrF4-BaF2-LaF3-AlF3-NaF) glass fiber pumped by an 1120-nm fiber laser. To our best knowledge, this is the first report of 784-nm (1G4 --> 3H5 transition) ASE in a Tm3+-doped fluoride fiber laser. Its effects on a 480-nm (1G4 --> 3H6 transition) blue laser were also discussed.