Eugeni M. Dianov

Performance of Bragg and long-period gratings written in N- and Ge-doped silica fibers under /spl gamma/-radiation

In-fiber Bragg and long-period gratings as well as Mach-Zehnder interferometers based on germanium- and nitrogen-doped silica fibers have been investigated under /spl gamma/-rays. The majority of the experimental results suggest that both types of gratings in both types of fibers are stable with respect to /spl gamma/-ray doses of up to 1.47 MGy.

Super-high-strength metal-coated low-hydroxyl low-chlorine all-silica optical fibers

High-purity KS-4V synthetic silica developed in the Silicate Chemistry Institute of the Russian Academy of Sciences is tested as the core material for radiation hardened optical fibers. Pure-silica-core fluorine-doped-silica-cladding optical fibers with polymer (acrylate) or metal (aluminum) coating are produced as the experimental samples. The light-reflecting fluorine-doped silica cladding is synthesized by the plasma outside deposition process. The aluminum coating technology used provides a very high strength of the fibers, unattainable for polymer coatings, and expands the fiber operating range up to 400/spl deg/C. It is established that the metal coating application can result in the annealing of the drawing-induced color centers with an absorption peak at 630 nm. Post-/spl gamma/-irradiation loss spectra in KS-4V-based fibers measured in 1-2 hours after 2 MGy irradiation at a dose rate of 8.3 Gy/s in the spectral range 350-700 nm are discussed. The 630 nm absorption peak is practically absent from the post-irradiation loss spectra of aluminum-coated KS-4V-based fibers.

/spl gamma/-radiation-induced absorption in pure-silica-core fibers in the visible spectral region: the effect of H/sub 2/-loading

/spl gamma/-radiation-induced absorption in the visible spectral region is studied in H/sub 2/-loaded and untreated optical fibers with high-OH low-Cl KU core and low-OH low-Cl KS-4V core. H/sub 2/-loading is found to suppress the low-dosage transient absorption band centered at 670 nm in KS-4V fibers. After irradiation to 1.7 MGy(Si), H/sub 2/-loaded fibers show losses many times lower than the untreated fibers. H/sub 2/-loaded and irradiated fibers are found to retain very high radiation resistance under subsequent irradiations even in the absence of molecular hydrogen. It is concluded that H/sub 2/-loading followed by pre-irradiation can be used as an efficient radiation hardening technique for pure-silica optical fibers.

Yb3+-doped double-clad fibers and lasers

We present results of the research and development of double-clad Yb3+-doped fibers for high-power fiber lasers. The quality of the fabricated fibers and optimization of reflecting Bragg gratings allowed us to demonstrate fiber lasers with a quantum efficiency close to 90%. These fiber lasers were used in Raman converters emitting at various wavelengths.

UV absorption and luminescence in silicon oxynitride prepared by hydrogen-free SPCVD-process

UV absorption and luminescence are investigated in bulk samples of silicon oxynitride prepared by a hydrogen-free SPCVD-process (surface plasma chemical vapour deposition). The UV absorption spectra, apart from the well-known silicon oxygen-deficient centre (Si-ODC), exhibit two unknown absorption bands with maxima at 5.77 and 4.54 eV and two unknown luminescence bands at 3.55 and 3.03 eV under laser excitation at 257 nm (4.83 eV). These new bands are supposed to be due to a nitrogen-modified silicon oxygen-deficient centre.

Application of reduced-pressure plasma CVD technology to the fabrication of Er-doped optical fibers

Abstract For the first time the reduced-pressure plasma CVD technology was applied to fabrication of active silica optical fibers with all-depressed index structure. Using surface plasma CVD method, fiber preforms with an Er-doped silica core and fluorine doped silica cladding have been prepared and tested. A possibility of high performance active fiber fabrication using the SPCVD has been demonstrated. An influence of fluorine co-doping on luminescence features of Er 3+ ions in a silica host has been examined. The erbium concentration-associated clustering effects in pure silica host synthesized by the SPCVD were compared with those in germanosilicate host synthesized by the MCVD.

Crystalline silver halide fibers with optical losses lower than 50 dB/km in broad IR region and their applications

For the first time crystalline silver halide optical fibers with optical losses lower than 50 dB/km in a broad IR region from 9 to 14 micrometers were fabricated by an extrusion process. The optical loss mechanism essential to the lowest absorption in silver halide materials and fibers, namely intraband absorption by free holes in the valence band is proposed. The crystalline fibers with Rayleigh-type (lambda) (superscript -4) optical scattering were obtained. An IR region near 13 micrometers in AgBrI fibers with optical losses of less than 10 dB/km was discovered. Non-aged, stable IR polycrystalline silver halide optical fiber cables with losses lower than 1 dB/m in the region from 3 to 20 micrometers are demonstrated. Various applications of the developed low- loss silver halide fibers in remote spectroscopic chemical sensing, non-contact temperature monitoring and IR laser power delivery are discussed.

Fabrication and investigation of single-mode highly phosphorus-doped fibers for Raman lasers

A technology has been developed for fabrication of single- mode fibers with a high level of phosphorous doping (10 - 17 mol% P2O5) in the core. Characteristics of such fibers intended for use in Raman lasers operating at 1.24 and 1.48 micrometers are investigated. A reduction of fiber drawing temperature and additional doping of the fiber core with fluorine allowed a reduction of optical losses below 1 dB/km in wavelength range 1.1 - 1.5 micrometers .

Performance of special radiation-hardened optical fibers intended for use in the telecom spectral windows at a megagray level

Gamma-radiation-induced absorption spectra (2.15 MGy(Si)) are compared in N-doped and pure silica fibers fabricated by surface plasma CVD-process under different regimes with the aim to reveal the chief absorption mechanisms in the telecom spectral windows and to work out an optimum fiber design. The long wavelength absorption edge is shown to be the main absorption mechanism at megagray doses. Its value increases with increasing bonded hydrogen concentration in the fiber glass network and is slightly greater in N-doped fibers. No nitrogen-related color centers have been revealed in the short wavelength loss edge, which is determined by chlorine impurity in silica.

Phosphosilicate-core single-mode fibers intended for use as active medium of Raman lasers and amplifiers

Highly phosphorus doped (7 - 17 mol%) single-mode fibers for the application in Raman laser have been manufactured. It has been established that with increasing the P2O5 concentration level, both optical losses and the fiber Raman gain coefficient increase. Using the fiber technology developed, the maximum efficiency of a single-cascaded Raman laser is achieved at a phosphorous pentoxide doping level of 12 - 14 mol% P2O5.