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We report the preparation of a high-purity optical-quality four-component glass of composition 68TeO2 -- 22WO3 -- 8La2O3 -- 2Bi2O3, containing (2.7+-0.5)x10-5 mol % OH groups. Its refractive index has been determined in the range 0.9 -- 5.45 mm using interference refractometry. The data are used to assess the dispersion and guidance characteristics of microstructured optical fibres potentially attractive for supercontinuum generation in the range 1 -- 5 mm

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.

Core–clad optical fibers were fabricated from high-purity As2S1.5Se1.5glass, and their properties were studied. The arsenic sulfo-selenide was prepared by melting a mixture of high-purity arsenic monosulfide, arsenic, and selenium. Optical fibers with core/clad diameters of 300/400 and 200/400 μm were fabricated by the double-crucible method. The minimum loss was found to be 60 ± 20 dB/km at 4.8 μm and 200–300 dB/km between 4 and 6 μm. The numerical aperture of the fibers was 0.28. A 1.5-m-long section of the fiber transmitted 6-W CO laser radiation. The average bending strength of the 400-μm-diameter fibers was 0.8 GPa.

As2Se3.4glass samples with controlled oxygen content in the range (1.4–7.9) × 10–2wt % were used to assess the effect of oxygen impurity on the IR absorption spectrum of the glass. The spectral dependence of the extinction coefficient for oxygen impurity was determined in the range 600–1400 cm–1. It was shown that the presence of 10–5wt % O gives rise to additional losses comparable to the intrinsic losses in the CO2lasing range.

Experimental data are presented on the effect of the Te evaporation rate on the efficiency of the removal of submicron carbon particles (major impurities in Te, present in amounts from 106to 5 × 108cm–3, depending on the purification procedure). By distilling a small amount of the melt, the effective separation coefficient was determined as a function of particle size. For 0.065- to 0.14-μm particles at a minimum evaporation rate of 3 × 10–7cm3/(cm2s), the separation coefficient lies in the range 9–100. As the evaporation rate increases to 2.5 × 10–5cm3 /(cm2s), the separation coefficient drops to 2–8. Among the factors influencing the purification efficiency is the floating (inverse sedimentation) of submicron carbon particles in molten Te, observed experimentally upon long-term holding.

We have prepared 28Si, 29Si and 30Si single crystals with enrichments above 99.9 at % and a silicon single crystal of natural isotopic composition. The oxygen and carbon concentrations in all the crystals are within 5x1015 cm-3, and the content of metal impurities is 0.01 -- 0.1 ppma. The refractive index of the crystals has been determined in the range 1.05-25.5 mm using interference refractometry, and its dispersion and material dispersion have been determined.

Raman spectra of TeO_2-based glasses doped with WO_3, ZnO, GeO_2,TiO_2,MoO_3, and Sb_2O_3 are measured. The intensity of bands in the Raman spectra of MoO_3–TeO_2 and MoO_3–WO_3–TeO_2 glasses is shown to be 80–95 times higher than that for silica glass. It is shown that these glasses can be considered as one of the most promising materials for Raman fiber amplifiers.

Experimental evidence is presented that, in a closed system containing the As2Se3melt and vapor, a temperature gradient gives rise to the chemical transport of carbon, combined with Se, from the hot (700–900°C) to the cold (600°C) zone. As a result, submicron-sized (0.07–0.18 μm) carbon inclusions are formed in the As2Se3melt. The results shed light on the role of second-phase inclusions in the degradation of the optical quality of glassy As2Se3.

The numerical aperture of core-clad multimode optical fibers with the core made from high-purity As2S3glass is measured by a far-field technique using a cw CO laser (5.3-6.3 µm). The lengths at which a steady-state modal distribution is reached are determined for optical fibers with metallic coatings, tetrafluoroethylene/difluoroethylene copolymer coatings, or immersion. Various factors affecting the numerical aperture of fibers with an unsteady-state modal distribution are examined.

Optical fibres have been fabricated for the first time from As2S3 glass containing chromium-doped ZnS and ZnSe crystals, and their optical loss and luminescence spectra have been measured in the mid-IR. In the spectral range 2 -- 3 mm, the optical loss in the fibres is 2 -- 4 dB m-1. The fibres have a broad luminescence band in the range 1.8 -- 3 mm, with a maximum near 1.9 mm, which is due to Cr2+ 5E -- 5T2 intracentre transitions in the II - VI host.

We have prepared 28Si, 29Si and 30Si single crystals with enrichments above 99.9 at % and a silicon single crystal of natural isotopic composition. The oxygen and carbon concentrations in all the crystals are within 5×1015cm-3, and the content of metal impurities is 0.01 — 0.1 ppma. The refractive index of the crystals has been determined in the range 1.05–25.5 μm using interference refractometry, and its dispersion and material dispersion have been determined.

Optical fibres have been fabricated for the first time from As2S3glass containing chromium-doped ZnS and ZnSe crystals, and their optical loss and luminescence spectra have been measured in the mid-IR. In the spectral range 2 — 3 μm, the optical loss in the fibres is 2 — 4 dB m-1. The fibres have a broad luminescence band in the range 1.8 — 3 μm, with a maximum near 1.9 μm, which is due to Cr2+5E — 5T2intracentre transitions in the II - VI host.

We report the preparation of a high-purity optical-quality four-component glass of composition 68TeO2— 22WO3— 8La2O3— 2Bi2O3, containing (2.7±0.5)×10-5mol % OH groups. Its refractive index has been determined in the range 0.9 — 5.45 μm using interference refractometry. The data are used to assess the dispersion and guidance characteristics of microstructured optical fibres potentially attractive for supercontinuum generation in the range 1 — 5 μm

Review: (synthesis conditions, influence of impurities, phase inhomogeneities, and gaseous bubbles on the optical properties; some experimental results for the ZrF4/BaF2/LaF3/AlF3/NaF system.