M.R.B. Andreeta

Growth of single-crystal photorefractive fibers of Bi12SiO20 and Bi12TiO20 by the laser-heated pedestal growth method

Abstract Photorefractive single-crystal fibers of Bi 12 SiO 20 up to 90 mm in length and Bi 12 TiO 20 up to 50 mm in length with diameters of 650–1200 μm were grown by the laser-heated pedestal growth (LHPG) method. Both Bi 12 SiO 20 and Bi 12 TiO 20 fibers were pulled from stoichiometric (6:1) melts at pulling rates of 0.3 and 0.2 mm/min, respectively, the feeding rate was 0.1 mm/min. Growth conditions, morphology and chemical composition of the grown fibers were studied. The possible mechanisms of crystallization of incongruently melting Bi 12 TiO 20 fiber from the stoichiometric melt were discussed. The energy-exchange effect was observed in the BSO fibers at the wavelength λ = 0.5145 μm .

Optical activity measurements in the photorefractive Bi12TiO20 single crystal fibers

Abstract In the present work the specific optical activity coefficient of the photorefractive Bi 12 TiO 20 single crystal fibers have been determined. The samples were illuminated by λ =0.6328 μ m and λ =0.5145 μ m. The proposed experimental technique is simple, fast and accurate. It is based on the automatic electronic phase shift detection in a dynamic polarimetric system. 6.62±0.06 deg/mm was obtained for λ =0.633 μ m and 10.0±0.2 deg/mm for λ =0.514 μ m.

Single-crystal SrTiO3 fiber grown by laser heated pedestal growth method: influence of ceramic feed rod preparation in fiber quality

The rapidly spreading use of optical fiber as a transmission medium has created an interest in fiber-compatible optical devices and methods for growing them, such as the Laser Heated Pedestal Growth (LHPG). This paper reports on the influence of the ceramic feed rod treatment on fiber quality and optimization of ceramic pedestal processing that allows improvements to be made on the final quality in a simple manner. Using the LHPG technique, transparent crack-free colorless single crystal fibers of SrTiO3 (0.50 mm in diameter and 30-40 mm in length) were grown directly from green-body feed rods, without using external oxygen atmosphere.

Two-wave mixing in photorefractive Bi(12)SiO(20) fibers.

We present what is to our knowledge the first experimental observation of the energy-exchange effect between two coherent beams in Bi(12)SiO(20) single-crystal optical fiber grown by the laser-heated pedestal growth technique.

Automatic diameter control system applied to the laser heated pedestal growth technique

We described an automatic diameter control system (ADC), for the laser heated pedestal growth technique, that reduces the diameter fluctuations in oxide fibers grown from unreacted and non-sinterized pedestals, to less than 2% of the average fiber diameter, and diminishes the average diameter fluctuation, over the entire length of the fiber, to less than 1%. The ADC apparatus is based on an artificial vision system that controls the pulling speed and the height of the molten zone within a precision of 30 mm. We also show that this system can be used for periodic in situ axial doping the fiber. Pure and Cr3+ doped LaAlO3 and pure LiNbO3 were used as model materials.

The influence of temperature gradients on structural perfection of single-crystal sillenite fibers grown by the LHPG method

Abstract Single-crysta fibers of Bi 12 SiO 20 and Bi 12 TiO 20 up to 90 mm in length with diameters of 200–1200 μm were pulled along the 〈001〉 and 〈011〉 crystallographic axis by the LHPG method. The powder X-ray diffraction and the electron-probe microanalysis were used for characterization of the grown fibers. The microstructure of sillenite fibers was studied by the chemical etching method. The dislocations, inclusions and striations are the main imperfections that were found in the fibers. The dislocation density equal to 1×10 5 pits/cm 2 was estimated on the ground of the etching pits using optical and electronic microscopy and was compared to that evaluated by the Tsivinskiis relation based on the axial temperature distribution in the fiber and on the elastic properties of the material. The conditions of the formation of microdefects are discussed in relation with the growth conditions, morphology and chemical composition of the grown fibers.

Laser heated pedestal growth of Sr2RuO4 single-crystal fibers from SrRuO3

Abstract We report the single-crystal growth of Sr 2 RuO 4 by the laser heated pedestal growth (LHPG) method. The fibers obtained were up to 30 mm in length and around 0.8 mm in diameter. They crystallized with the K 2 NiF 4 structure, space group I4/mmm and with lattice parameters a = 3.869(1) A , c = 12.745(5) A . They were easily cleaved along the growth axis, parallel to the (0 0 1) plane. The single-crystal fibers were characterized by scanning electron microscopy, electron probe micro-analysis and X-ray diffraction.

Microwave dielectric permittivity and photoluminescence of Eu2O3 doped laser heated pedestal growth Ta2O5 fibers

We report the microwave dielectric properties and photoluminescence of undoped and europium oxide doped Ta2O5 fibers, grown by laser heated pedestal growth technique. The effects of Eu2O3 doping (1–3mol%) on the structural, optical, and dielectric properties were investigated. At a frequency of 5GHz, the undoped material exhibits a dielectric permittivity of 21 and for Eu2O3 doped Ta2O5 samples it increases, reaching up to 36 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value. For this wide band gap oxide, Eu3+ optical activation was achieved and the emission is observed up to room temperature. Thus, the transparency and high permittivity make this material promising for electronic devices and microwave applications.

SrTiO3 single crystal fibers grown by laser-heated pedestal growth (LHPG)

Abstract Single crystal fibers can be grown from sintered ceramic rods using the Laser Heated Pedestal Growth (LHPG) method. In this paper we report the preparation and characterization of sintered SrTiO3 ceramics to use as nutrient in the fiber growth. Single-crystal fibers were grown from ceramics feedrods with different growth parameters and characterized by X-Ray Diffraction in order to determine the preferential growth orientation and the crystallographic structure.

Microstructure of single-crystal sillenite fibers

Abstract Single-crystal fibers of Bi12SiO20 and Bi12TiO20 up to 90 mm in length with diameters of 200-1200 pm have been pulled along the and crystallographic axis by the LHPG method. The powder X-ray diffraction and the electron-probe microanalysis have been used for characterization of the as-grown fibers. Microstructure of the sillenite fibres has been studied by the chemical etching method. The dislocations, inclusions and striations have been found to be the main imperfections in the as-grown fibers. The dislocation density has been estimated on the ground of the etching pits using optical and electronic microscopy and compared with that evaluated by the Tsivinskiis relation. The conditions of formation of microdefects are discussed in relation with the growth conditions, morphology and chemical composition of the as-grown fibers.