G. E. Snopatin

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.

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.

Single-mode As-S glass fibers

Single-mode As–S glass fibers with a core diameter from 3 to 20 μm and a clad diameter of 125 μm are prepared by the double-crucible method. The cutoff wavelength of the fibers is 0.9–6 μm. The lowest transmission losses in the fibers at 2.2–2.3 μm are ∼100 dB/km, and their mean bending strength is 800–1000 MPa.

Recent developments in As-S glass fibres

Abstract Recent developments in As–S glass fibres showed that increase in degree of purity of As–S glasses allowed optical fibres to be fabricated with minimum optical losses of multimode optical fibres 23–45 dB/km at 2.2–2.7 μm, 50–70 dB/km at 3.2–3.6 μm, 200–300 dB/km at 4.1–4.7 μm and 300–500 dB/km at 5.0–5.5 μm. The bending strength of optical fibres with diameter of 400 μm increased from ∼0.5 to >1.2 GPa. Core and clad glass compositions were As40S60 and As38S62, respectively.

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.

Optical absorption and structure of impurity Ni2+ center in tungstate–tellurite glass

Absorption spectra of Ni ions in 22WO3–78TeO2 tungstate-tellurite glass were studied and Ni extinction coefficient spectral dependence was derived in the 450 – 2700 nm wavelength range. Computer modeling of the glass structure proved Ni ions to be in trigonal-distorted octahedral environment in the tungstate-tellurite glass. Tanabe-Sugano diagram for such an environment was calculated and good description of the observed spectrum of Ni ion was obtained. Basing on both absorption spectral range width and the extinction coefficient, nickel should be considered among the most strongly absorbing impurities in the tellurite glasses.

Extinction coefficient of Ni2+ in (TeO2)0.78(WO3)0.22 glass

The absorption spectra of (TeO2)0.78(WO3)0.22 glasses containing 0.01–1.0 wt % NiO have been measured at wavelengths from 450 to 2700 nm, and the spectral dependence of the extinction coefficient of Ni2+ in the glasses has been obtained. In the absorption bands centered at 810 and 1320 nm, the extinction coefficient is 20.2 ± 0.8 cm−1 (870 ± 35 dB/(km ppmw)). According to the spectral range of its absorption and its extinction coefficient, nickel is a strongly absorbing impurity in tellurite glasses. The present results can be used to formulate sound nickel concentration limits in tellurite glasses for fiber-optic applications.

X-ray fluorescence determination of the macroscopic composition of As-S, As-Se, and As-S-Se glasses

An X-ray fluorescence technique has been developed for determination of the macroscopic composition of As-S-Se, As-S, and As-Se chalcogenide glasses. Reference samples for calibration have been prepared by direct elemental synthesis. The calibration error has been estimated.

Purification of glass melts in the As-Se system with vacuum distillation

The behavior of macrocomponents and impurities during vacuum distillation of glass melts in the As-Se system with arsenic concentrations of 30 and 40 at % in closed and open systems has been investigated. The possibility of using vacuum distillation in an open system for purifying arsenic selenide glass melts from oxygen and hydrogen impurities has been demonstrated.