Single Crystalline Fibers Research Articles

Power scaling limits of diffraction-limited fiber amplifiers considering transverse mode instability.

An empirical TMI threshold formula is derived based on a recently developed model and used to analyze the power-scaling performance of ytterbium-doped silica glass and YAG (Y3Al5O12) and lutetia (Lu2O3) single-crystalline fiber amplifiers. Overall, the single-crystalline fiber lasers are found to scale potentially to higher average powers due to their higher thermal conductivities compared to silica glass. This work serves as a useful extension to earlier works and shines significant new light on optimal fiber and amplifier designs for maximum average output power with TMI considered.

Solvent-free autocatalytic supramolecular polymerization.

Solvent-free chemical manufacturing is one of the awaited technologies for addressing an emergent issue of environmental pollution. Here, we report solvent-free autocatalytic supramolecular polymerization (SF-ASP), which provides an inhibition-free template-assisted catalytic organic transformation that takes great advantage of the fact that the product (template) undergoes a termination-free nucleation-elongation assembly (living supramolecular polymerization) under solvent-free conditions. SF-ASP allows for reductive cyclotetramerization of hydrogen-bonding phthalonitriles into the corresponding phthalocyanines in exceptionally high yields (>80%). SF-ASP requires the growing polymer to form hexagonally packed crystalline fibres, which possibly preorganize the phthalonitriles at their cross-sectional edges for their efficient transformation. With metal oleates, SF-ASP produces single-crystalline fibres of metallophthalocyanines again in exceptionally high yields, which grow in both directions without terminal coupling until the phthalonitrile precursors are completely consumed. By taking advantage of this living nature of polymerization, multistep SF-ASP without/with metal oleates allows for the precision synthesis of multi-block supramolecular copolymers.

Micro-pulling-down growth of long YAG- and LuAG-based garnet fibres: advances and bottlenecks

A technological advance in shaped μ-PD crystal growth provided us with high-quality single crystalline fibres of rare-earth garnets with the good longitudinal transparency and light attenuation length of up to 1 m.

Single-Crystalline Fibers of Deuterated Potassium Dihydrogen Phosphate

Single-crystalline fibers have distinct structures and optical properties comparing with the bulk crystals. In this article, two types of single-crystalline fibers of deuterated potassium dihydrogen phosphate (K(H1−xDx)2PO4, DKDP) are obtained by rapid growth in room-temperature supersaturated solution. X-ray diffraction analysis reveals that these DKDP single-crystalline fibers belong to tetragonal (I-42d) and monoclinic (P21/c) phases, respectively. The crystal structure of the tetragonal DKDP single-crystalline fiber is identical to that of the bulk DKDP tetragonal crystal reported. The lattice parameters of the monoclinic DKDP fiber (with the deuterium content of 55%) are a = 14.6571 Å, b = 4.5187 Å, c = 18.6962 Å, and β = 108.030°, which is a new crystal phase of DKDP. The monoclinic DKDP single-crystalline fiber is metastable at the present experimental condition and readily transit to the corresponding DKDP tetragonal phase in solution and in solid by grinding. The optical experiment shows that the highly deuterated tetragonal DKDP single-crystalline fiber possesses excellent optical guided-wave and effective second-harmonic generation properties. DKDP single-crystalline fibers are expected to be the suitable candidates for fabrication of the miniaturized nonlinear optical devices.

Low-loss 'crystalline-core/crystalline-clad' (C4) fibers for highly power scalable high efficiency fiber lasers.

We report the latest progress in fabrication and laser performance of the fully crystalline double-clad 'Yb:YAG-core/undoped-YAG-clad' fibers grown by the hybrid crystal growth method. The single-crystalline ytterbium (Yb) doped yttrium aluminum garnet (YAG) fiber cores were grown by the laser heated pedestal growth (LHPG) method, and the single-crystalline undoped YAG claddings were grown by the liquid phase epitaxy (LPE) technique, in which the single-crystalline Yb:YAG cores were used as the growth seeds. The key parameters of the hybrid-grown 'crystalline core/crystalline clad' (C4) fibers, including material composition, crystal structure, and fiber propagation loss, were characterized. The results confirmed that the grown C4 fibers, indeed, have both the single-crystalline fiber core and single-crystalline fiber clad. By utilizing a double-clad low-loss C4 fiber as a diode-cladding-pumped laser gain medium, we realized a fiber laser with the optical-to-optical conversion efficiency of 68.7% versus the incident pump power.

Optical quality tetragonal phase single-crystal fiber of potassium di-hydrogen phosphate with efficient second-harmonic generation

Optical quality tetragonal phase quasi one-dimensional single-crystalline fibers of potassium di-hydrogen phosphate with a large length-to-diameter ratio and high flexibility have been grown. Efficient guided-wave optical second harmonic generation is achieved along the growth axis. The single-crystal fibers open great potential of potassium di-hydrogen phosphate crystals in micro-photonic applications.

Structural, optical, and electrical properties of SmNbO4

Rare-earth orthoniobates constitute a class of materials that has been exploited due to their interesting physical properties depending on the lanthanide element. Besides paramagnetism, ferroelasticity, and negative compressibility, these materials are known by their interesting optical properties and mixed types of conduction processes (protonic, ionic, and electronic). In this work, two types of SmNbO4 samples were studied: polycrystalline samples, prepared by a sol-gel route using the Pechini method, and single crystalline fibres grown by the Laser Floating Zone technique. These samples were structurally characterized based on powder and single-crystal X-ray diffraction studies. A metastable tetragonal phase, stabilized by grain size, was identified in the synthesized powders. After a sintering process of such powders, a single monoclinic phase was obtained. Complementarily, scanning electron microscopy and Raman spectroscopy analyses were performed to these samples. Photoluminescence and photoluminescence excitation spectroscopic studies allowed identifying more than one optically active centre of the trivalent samarium ion in the analysed material. Impedance spectroscopy measurements have shown a large variation of the ac conductivity as a function of temperature, assigned to a protonic conduction and to native ionic conduction mechanisms.

Yb-doped LiGd1−xLux(WO4)2 single crystal fibers grown from the melt and optical characterization

As a function of lutetium concentration, Yb(1at%)-doped LiGd1−xLux(WO4)2 phases have been synthesized by solid state reaction. For x≤0.025, a limited solid solution corresponding to the substitution of Gd3+ by Lu3+ in LiGd(WO4)2 compound was observed. In another hand, for x≥0.8 a limited solid solution corresponding to the substitution of Lu3+ by Gd3+ in LiLu(WO4)2 was obtained. Different single crystalline fibers belonging to the Yb (1at%)-doped LiGd1−xLux(WO4)2 system with diameter average 600µm and length up to 30mm have been grown by micro-pulling down method. In the stationary stable growth regime, the crystallization interface was flat and meniscus length reaches 120µm±20. An overheating of the melt causes a strong Li2O loss and composition change in the equilibrium diagram allowing growth instabilities and crystal disconnection from the molten zone. The optical characterizations have been performed. Decay time has been recorded for the 1at% Yb3+ doped fibers.

Cerâmica transparente de Y2O3 obtida por sinterização rápida em forno de radio frequência sob atmosfera de vácuo dinâmico

Monocristais de ítria (Y2O3) são importantes materiais hospedeiros para lasers. Entretanto, seu elevado ponto de fusão (2450 ºC) dificulta o processo de crescimento de monocristais. Uma alternativa para a obtenção de ítria policristalina com propriedades similares às dos monocristais é a fabricação de cerâmicas transparentes. Desta forma, este trabalho teve o propósito de desenvolver uma metodologia para fabricar cerâmicas transparentes de ítria, utilizando-se um forno de indução eletromagnética que permite o uso controlado de atmosferas inertes ou redutoras e pode atingir temperaturas próximas a 2000 ºC, com taxas de aquecimento maiores que 100 ºC/min. Os pós-precursores foram preparados por meio de reação do estado sólido usando 3% em mol de ZrO2 como aditivo. As amostras foram conformadas em discos com 12 mm de diâmetro e 1 mm de espessura sob uma pressão uniaxial de 50 MPa e isostática de 350 MPa. Em seguida, foram sinterizadas a 1800 e 1900 ºC com tempos de sinterização de 1 e 5 h. Difração de raios X e microscopia eletrônica de varredura foram usadas na caracterização estrutural e microestrutural das amostras e sua transmissividade ótica foi medida por meio de espectrofotometria. Através da sinterização em forno de indução foi possível obter cerâmicas com até 60 % de transmissão em linha na região de 800 nm em tempos de sinterização menores que os descritos na literatura.

Reactive molten core fabrication of glass-clad amorphous and crystalline oxide optical fibers

Described herein are glass-clad optical fibers, fabricated using a molten core fiber draw process, comprising oxide cores in the Bi2O3 – GeO2 system. More specifically, the fibers utilized a borosilicate glass cladding with core compositions in the initial preform ranging from un-reacted crystalline Bi2O3-rich (Bi2O3 + GeO2) powders to stoichiometric crystalline Bi12GeO20. Fibers drawn from the as-purchased crystalline Bi2O3-rich powders were amorphous with a transmission of about 80% at 1.3 μm. Fibers drawn from the crystalline Bi12GeO20 core contained a mixture of crystalline bismuth germanate (Bi2GeO5) and bismuth oxide (δ-Bi2O3/BiO2-x). While representing an initial proof-of-concept, this work shows that commercially-relevant draw processing can be employed to yield fibers with core composition that are very difficult to fabricate using conventional methods and that the molten core method further enables in situ reactive chemistry to take place during fiberization resulting in amorphous or crystalline oxide core fibers depending on initial core composition. Perhaps more importantly is that optical fibers possessing acentric, hence optically nonlinear, oxide crystals can be realized in a scalable manufacturing manner though further optimization is required both of the core chemistry and process conditions in order to achieve a single phase and single crystalline fiber.

Growth, structural and optical characterizations of LiLa(1−x)Eux(WO4)2 single-crystalline fibers by the micro-pulling-down method

Transparent and uniform LiLa(1−x)Eux(WO4)2 single-crystalline fibers where x=0.005, 0.01, 0.03, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25 and 1.0, with an average of 20–40mm length were obtained by the micro-pulling-down method aiming structural and optical characterization. The optimum pulling rate was found to depend on the difference between alkali and rare earth ionic radii. Rietveld analysis from X-ray diffraction data and excitation spectroscopy at room temperature were applied to investigate the lattice changes due to the Eu3+ incorporation in the host. LiLa(1−x)Eux(WO4)2 crystal fibers present red emission due to the electric dipole 5D0→7F2 transition under 395nm excitation showing a concentration quenching around 20mol% of doping. The excitation spectra of the 7F0→5D0 transition show small changes in the Eu3+ surroundings as function of dopant concentration.

Basic study of single crystal fibers of Pr:Lu3Al5O12 scintillator for gamma-ray imaging applications

Abstract Single-crystalline fibers were grown from 0.25, 0.70, and 1.50 mol% Pr-doped Lu 3 Al 5 O 12 (LuAG) melts by the micro-pulling down (μ-PD) method with a diameter of 0.3–0.5 mm and a length of about 200 mm. They were cut to 10 mm long specimens, and their scintillation properties, including light yield and decay time profile, were examined. These results were compared with corresponding properties of the specimens (0.8×0.8×10 mm 3 ) cut from the bulk crystals produced by conventional Czochralski (CZ) growth. The μ-PD-grown fibers demonstrated relatively low light yield and had the same decay time constant when compared with those of the samples cut from the CZ-grown crystals. The fiber crystals were used to assemble scintillating arrays with dimensions of O 0.5×10 mm 2 ×20 pixels and O 0.3×10 mm 2 ×30 pixels coated by a BaSO 4 reflector. After optical coupling with a position sensitive photomultiplier tube, the fiber-based arrays demonstrated acceptable imaging capability with a spatial resolution of about 0.5 mm.

Single and polycrystalline mullite fibres grown by laser floating zone technique

The laser floating zone technique was used to grow large 2Al 2O 3–SiO 2 mullite fibres (up to 1.6 mm in diameter and 40 mm in length). The fibres grown at 10 mm/h are single crystalline in nature, while those pulled at higher rates (40 and 100 mm/h) are polycrystalline with a cellular microstructure. The crystals are highly [0 0 1] textured with respect to the fibre axis, as determined by X-ray diffraction analysis. The Raman spectra taken at different orientations corroborate the strong anisotropy observed by X-ray and SEM on both single crystalline and textured polycrystalline samples. Four point bending tests and ultramicroindentation Vickers experiments were performed at room temperature in order to characterize the mechanical properties. The presence of lamellar inclusions in the single crystalline fibres decreases the flexural strength (431 MPa) and the fracture toughness (1.2 MPa.m 1/2) compared to the polycrystalline ones (631 MPa and 1.6 MPa.m 1/2). However, the absence of grain boundaries in the single crystals leads to higher ultramicrohardness ( H V = 15.6 GPa) and Young's modulus ( E = 170 GPa) than those of the polycrystalline fibres (14.2 and 145 GPa), where a glassy intergranular phase exists.

Drawing of single-crystal and glass-clad lithium tantalate fibers by the laser-heated pedestal growth method

Lithium tantalate (LT) single-crystalline fibers with various growth conditions were obtained using the laser-heated pedestal growth (LHPG) method. The fibers can be produced with a diameter down to 70 µm and tens of centimetres in length by using different pulling rates. Preliminary experiments also showed that the LT fibers can be electrically poled for quasi-phase matching. To facilitate wave propagation with low loss, glass-clad LT fibers were fabricated by a co-drawing LHPG method for the first time. A vacuum apparatus was developed to eliminate the bubbles from incongruent evaporation of lithium oxide during the drawing of the glass-clad LT fibers. The glass-clad fibers are classified into two different categories by the measurements of refractive index profiles. One is a step-index fiber and the other is a graded-index fiber. Both fiber types are multimode at present, but single-mode LT fibers could be fabricated with the high-precision control of the LHPG systems.

BGO fibers growth by [formula omitted]-pulling down technique and study of light propagation

There is a great progress in inorganic scintillators study, new crystals composition have been investigated, novel scintillation mechanism have been discovered, and additional application have been appeared especially imaging for medical application. There are a different academic and industrial program for the improvement of the scintillators crystals and applications. Since fifteen years ago, fibers geometry is an attractive topic for a large wide of application such lasers and scintillation. In spite of the big scientific and industrials efforts for fibers valorisation, still now there aren’t a concrete applications based on fibers design. This problem can be related to the application limit based on fibers design, single crystal fibers packaging, and the limit of fibers single crystal growth technology compared to the bulk crystals elaboration.Our teems are involved in different national and international fibers program. We are working on Bi4Ge3O12 (BGO) single crystal fibers using micro-pulling down technology. The BGO crystals melt congruently at 1060∘C and have many excellent characteristics such as large density, short radiation length, light output as large as 10% of NaI:Tl, non hygroscopic, absence of cleavage, mechanical rigidness, high resistivity to radiation damages and price is rather low compared to LSO crystals. In this work, we present long BGO single crystalline fibers (Figure 1) grown by μ-PD. The obtained fibers have good qualities, the optical properties will be discussed and we will evaluate their scintillation characteristics.

Transferring Self-Assembled, Nanoscale Cables into Electrical Devices

This study details a new derivative of the contorted HBCs that self-organizes into one-dimensional, single-crystalline fibers. X-ray diffraction, transmission electron microscopy, and electron diffraction studies show that they have an orthorhombic unit cell with dimensions of 5.8 nm x 4.5 nm x 0.45 nm. Each fiber is composed of a few thousands columns. A method is put forth that utilizes elastomer stamps to manipulate and position isolated fibers in organic field effect transistors.

Growth of LiYF 4 single-crystalline fibres by micro-pulling-down technique

Pure yttrium–lithium tetrafluoride (YLF) fibres have been successfully grown by the micro-pulling-down (μ-PD) technique in resistive mode. The influence of the growth atmosphere and starting melt composition on growth process were studied. YLF fibres grown from Li-rich melt (5 mol%) contain more than 70% of colourless, transparent and single-phase material. After a short length of the peritectic transient (≈10 mm), the fibres were uniform in diameter (800 μm) and quite long (≈60 mm). This work reports a suitable and reproducible growth process for high-quality YLF single-crystalline fibres.

Optical properties of lithium fluoride fibers grown by micro-pulling-down method

Fluoride single-crystalline fibers were grown by the micro-pulling-down (μ-PD) technique. The optical properties of the LiF fiber and the bulk crystal (grown by Czochralski technique) were compared. Both samples were irradiated with 40 Mrad of gamma rays at room temperature and color centers were successfully produced. The emission spectra of the fiber and the bulk crystal when excited at 447 nm show the typical broad emission bands related to the F 3 + and F 2 centers, with peaks at 535 and 650 nm, respectively. Both spectra contain a very strong emission band centered at 1120 nm with the same half width of 1350 cm −1 when excited with a InGaAs diode laser at 968 nm. These results indicate a potential use of these new LiF fibers in miniaturized active optical devices.

Growth and characterization of LiF single-crystal fibers by the micro-pulling-down method

Good optical quality LiF single-crystalline fibers ranging from 0.5 to 0.8mm in diameter and 100mm in length were successfully grown by the micro-pulling-down technique in the resistive mode. A commercial equipment was modified in order to achieve suitable conditions to grow fluoride single-crystalline fibers.

Growth of optically active p-phenylene needles on mica

Structural and optical properties of p-phenylene oligomers ( p- nP, n=4, 5, 6) grown on mica (0 0 0 1) are investigated via low energy electron diffraction (LEED) using a multi-channelplate LEED as well as linear absorption spectroscopy and fluorescence microscopy. Single-crystalline fibres of laying p-6P molecules with lengths of up to 1 mm are grown at elevated mica surface temperatures. The needles are mutually parallel oriented and form large domains of size 20×10 mm 2. Their orientation on the surface is controlled by interaction with surface dipole fields. These fibres allow us easy polarization control of absorbed ultraviolet and emitted blue light.