V.S. Shiryaev

High-purity chalcogenide glasses for fiber optics

The data on the present degree of purity of chalcogenide glasses for fiber optics, on their methods of production and on the properties, which are essential for their actual application, are generalized. The content of limiting impurities in the best samples of chalcogenide glasses is 10–100 ppb wt.; of heterophase inclusions with size of about 100 nm is less than 103 cm−3. On the basis of chalcogenide glasses the multimode and single mode optical fibers are produced with technical and operation characteristics sufficient for a number of actual applications. The minimum optical losses of 12–14 dB/km at 3–5 µm are attained in the optical fiber from arsenic-sulfide glass. The level of losses in standard chalcogenide optical fibers is 50–300 dB/km in 2–9 µm spectral range. The factors, affecting the optical absorption of glasses and optical fibers, are analyzed, and the main directions in further development of chalcogenide glasses as the materials for fiber optics are considered.

Demonstration of CO 2 -laser power delivery through chalcogenide-glass fiber with negative-curvature hollow core

A technologically simple optical fiber cross-section structure with a negative-curvature hollow-core has been proposed for the delivery of the CO2 laser radiation. The structure was optimized numerically and then realized using Te20As30Se50 (TAS) chalcogenide glass. Guidance of the 10.6 µm СО2-laser radiation through this TAS-glass hollow-core fiber has been demonstrated. The loss at λ=10.6 μm was amounted ~11 dB/m. A resonance behavior of the fiber bend loss as a function of the bend radius has been revealed.

Chalcogenide glasses doped with Tb, Dy and Pr ions

Abstract Optically homogeneous As–Se and As–S–Se glasses doped with the ions of rare-earth elements (REE), i.e. praseodymium, dysprosium and terbium up to 9000 wt. ppm were synthesized. A technique for introduction of REE into chalcogenide glasses (CG) is based on solidification of the melt of glass-forming compounds with the dopants of REE iodide and the time–temperature modes minimizing glass crystallization and dopant clustering. Microhomogeneity and absorption of the produced samples of the doped glasses were studied in the middle IR range. A spectral dependence of absorption by REE ions was investigated and the extinction coefficients were determined for the most intensive absorption bands of the ions of praseodymium, dysprosium and terbium. Luminescence properties of CG doped with Tb3+ were investigated at 4–5 μm. The optical fibers based on arsenic selenide doped with terbium were manufactured with optical losses of 1.5 dB/m at 6–9 μm and a bending strength of 0.6 GPa.

Low loss Ge-As-Se chalcogenide glass fiber, fabricated using extruded preform, for mid-infrared photonics

Chalcogenide glass fibers have attractive properties (e.g. wide transparent window, high optical non-linearity) and numerous potential applications in the mid-infrared (MIR) region. Low optical loss is desired and important in the development of these fibers. Ge-As-Se glass has a large glass-forming range to provide versatility of choice from continuously varying physical properties. Recently, broadband MIR supercontinuum generation has been achieved in chalcogenide fibers by using Ge-As-Se glass in the core/clad. structure. In the shaping of chalcogenide glass optical fiber preforms, extrusion is a useful technique. This work reports glass properties (viscosity-temperature curve and glass transition) and optical losses of Ge-As-Se fiber fabricated from an extruded preform. A robust cut-back method of fiber loss measurement is developed and the corresponding error calculation discussed. MIR light is propagated through 52 meters of a fiber, which has the lowest loss yet reported for Ge-As-Se fiber of 83 ± 2 dB/km at 6.60 μm wavelength. The fiber baseline loss is 83-90 dB/km across 5.6-6.8 μm, a Se-H impurity absorption band of 1.4 dB/m at 4.5 μm wavelength is superposed and other impurity bands (e.g. O-H, As-O, Ge-O) are ≤ 20 dB/km. Optical losses of fiber fabricated from different positions of the extruded preform are investigated.

Optical fibers based on As–S–Se glass system

The core-clad optical fibers with polymer coating based on As-S-Se glass have been manufactured with the aim of measuring their optical and strength parameters for potential use in the middle infrared. The glass compositions, As 40 S 30 Se 30 and As 40 S 33 Se 27 , were chosen as a core and a clad, respectively. To prepare sulfoselenide glasses and fibers we used two main variants, i.e., the direct melting of initial elements and using arsenic monosulfide as an arsenic-containing component. The core-clad-optical fibers were drawn by the double-crucible method with the ratio of core/ cladding diameters (in μm) 300/400, 200/400 and 100/400. The minimum loss measured by the two-point method was equal to 0.7 dB m 1 at 5.5 μm. It is the best result on As-S-Se core-clad fibers with comparable content of sulfur and selenium. The numerical aperture (NA), found as the sine of half of the angle of the power spatial distribution in the far zone, has also been measured in 2 fibers and is 0.35 and 0.2. The average mechanical bending strength was equal to 0.8 GPa.

High-Purity As-S-Se and As-Se-Te Glasses and Optical Fibers

We describe a procedure for the preparation of As-S-Se and As-Se-Te glasses with low contents of gas-forming impurities (hydrogen, oxygen, and carbon) via melting of extrapure-grade elements in an evacuated silica ampule and purification of the melt by chemical distillation. The impurity concentrations in the glasses thus prepared have been reduced to the following levels: hydrogen, <0.02; oxygen, 0.2; carbon, <0.02; silicon, <0.4 ppm by weight. Using the double-crucible method, we have fabricated glass fibers with various ratios of the core and cladding diameters (1: 25 to 9: 10), protected with a tetrafluoroethylene/1,1-difluoroethylene copolymer coating, which have an average bending strength of 0.5–1 GPa. The minimal optical losses are 150 dB/km at 6.6 μm in multimode As-Se-Te glass fibers and 60 dB/km at 4.8 μm in As-S-Se glass fibers. The effect of microinhomogeneities in the melt on the optical performance of arsenic sulfoselenide glass fibers fabricated by the double-crucible method is examined.

Stability of the Optical and Mechanical Properties of Chalcogenide Fibers

The variations in the optical losses and bending strength of high-purity As–S, As–Se, As–S–Se, and As–Se–Te glass fibers during storage in air were studied. The optical properties and strength of fibers with reflecting clads and well-protected surfaces were shown to be sufficiently stable for practical applications. The optical and mechanical properties of uncoated fibers degrade during storage because of adverse surface processes.

Preparation of High Purity Te-Rich Ge-Te-Se Fibers for 5–15

Te rich glasses in the ternary Ge-Te-Se system are stable against crystallization and remain transparent enough for application in the far infrared beyond 15 μm. Four protocoles of preparation of highly-purified Te-rich Ge-Te-Se glasses are developed and compared. These methods are based on different distillation procedures to remove water, oxides, hydrogen and carbon impurities from glasses. The final residual impurity content in glasses was determined by the IR spectroscopy and laser mass spectrometry. Then, unclad optical fibers were drawn from each synthetized glass. At room temperature, the minimum of attenuation is about 7 dB/m at 10.6 μm whatever the purification procedure, showing that the residual optical losses are intrinsic to the chemical nature of the glasses. On the other hand, at 77 K, the optical losses are lowered to 1 dB/m confirming that losses are mainly due to the high charge carrier concentration inherent to the semi-conducting behavior of these glasses. Finally, this low level of losses is rather a promising news in view of application in space where optical filtering devices working beyond 15 μm are needed.

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Abstract Fluoride glasses, for the production of IR optical fibers, have a tendency to crystallization. The crystallization of fluoride glasses is one of the main reasons for non-intrinsic optical losses due to scattering in fibers. The crystallization kinetics of 53ZrF4–20BaF2–4LaF3–3AlF3–20NaF (ZBLAN), 53.8HfF4–20.1BaF2–5CeF3–3.1AlF3–17NaF–1.2InF3 (HBCANI), 12.3BaF2–12.3SrF2–12.3CaF2–12.3MgF2–36AlF3–12.3YF3–2.5LaF3 (BSCMAYL), 30InF3–10YF3–25BaF2–5SrF2–10ZnF2–10GaF3–6NaF–4PbF2 (InYBSNZnGaPb) fluoride glasses was investigated at the early stages of glass-to-crystal transformation. The experiment consisted in measuring the contents and sizes of microcrystals in glass interiors as a function of treatment time of the sample at constant temperature. The contents and sizes of crystals were determined by the method of laser ultramicroscopy. Investigations were carried out in the range between glass-forming and softening temperatures. The nucleation rate, W, the linear growth rate of crystals, V, and the temperature dependence of these kinetic parameters were found at the level of conversion of glass-crystal between 10−6% and 10−3%. The nucleation rate was maximum of ∼200 nuclei /( s cm 3 ) near 260°C in ZBLAN, ∼300 nuclei /( s cm 3 ) near 280°C in HBCANI, ∼280 nuclei /( s cm 3 ) near 400°C in BSCMAYL and ∼650 nuclei /( s cm 3 ) near 310°C in InYBSNZnGaPb glass. The results of investigation are useful for optimization of the heat treatment mode of fluoride glasses and to understanding of the processes critical to the optical homogeneity of these glasses.

m Infrared Range

The optical losses in sulfoselenide glass fibers fabricated by the double-crucible method are shown to rise in going from the first-drawn portion to the back end of the fiber. Optical microscopy, IR and Raman spectroscopy, energy-dispersive x-ray microanalysis, and differential scanning calorimetry data indicate that fiber drawing is accompanied by the development of microinhomogeneities of the chemical and phase compositions of the melt, which are responsible for the increased scattering losses. The microinhomogeneities originate from phase segregation of the molten glass.