Alexei N. Guryanov

Bi-Doped Optical Fibers and Fiber Lasers

The current state of the art in infrared Bi-doped fiber laser research is reviewed. The relevant fiber glass compositions and fiber technologies are introduced. Lasers operating on transitions ranging from 1.15 to 1.55 μm occurring in the bismuth active centers and their energy level schemes are discussed on the basis of the spectroscopic properties of these centers. Continuous-wave fundamental-mode power levels ranging from a few mW near 1.55 μm up to 16 W near 1.16 μm and 22 W near 1.46 μm have been demonstrated in recent years.

Absorption, Gain, and Laser Action in Bismuth-Doped Aluminosilicate Optical Fibers

In this study, bismuth-doped fiber lasers operating at the wavelength of 1179 nm with an optical efficiency of up to 28% are realized. The fiber gain upon 1-¿m pumping declines, while the unsaturable absorption increases with increasing the small-signal absorption. We conclude that up-conversion and excited-state absorption are responsible for limiting the efficiency of such lasers.

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.

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 .

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.

Anti-Stokes luminescence in Bismuth-doped silica and germania-based fibers

Luminescence excitation spectra of active centers in bismuth-doped vitreous SiO(2) and vitreous GeO(2) optical fibers under the two-step excitation have been obtained for the first time. The results revealed only one bismuth-related IR active center formed in each of these fibers. The observed IR luminescence bands at 1430 nm (1650 nm) and 830 nm (950 nm), yellow-orange (red) band at 580 nm (655 nm), violet (blue) band at 420 nm (480 nm) belong to this bismuth-related active center in the vitreous SiO(2) (vitreous GeO(2)), correspondingly.

Ultraviolet absorption and excess optical loss in preforms and fibers with high-germanium content

Nature of excess optical loss in fibers with high (up to 35 mol.%) GeO2 content silica core was studied experimentally. The absorption and scattering loss dependences on the drawing conditions were studied as well as the behavior of germanium-related oxygen- deficient centers (GODC) absorbing in UV spectral region. The peculiarity of such fibers was found to be in the drastic increase of the absorption and scattering loss when the core diameter diminish up to 3-3.5 micrometers . According to the excess loss analysis the absorption loss is caused by the enhanced GODC formation and the Ge-related drawing-induced defects. The excess scattering loss which dominates is assumed to be due to azimuthal and longitudinal core inhomogeneities caused by hydrodynamical instabilities of viscous glass during the fiber drawing. The germanium diffusion effect on optical loss is discussed.

Low-loss hybrid fiber with zero dispersion wavelength shifted to 1 µm.

We proposed and investigated a novel type of all-glass hybrid fiber where light is confined in the low-index core due to both total internal reflection and coherent Fresnel reflection (a photonic bandgap mechanism). The hybrid mode has an anomalous dispersion of 13 ps/(nm km) at 1064 nm and low loss (~6 dB/km), and it can be easily excited by splicing with a single-mode step-index fiber. The compression of positively chirped 8 ps pulses down to 330 fs was demonstrated with the fabricated hybrid fiber.

CW highly efficient 1.24-μm Raman laser based on low-loss phosphosilicate fiber

Extremely simple and efficient 1.24 micrometers phosphosilicate fiber-based Raman laser was developed. The cavity of the Raman laser was formed by the Bragg gratings written directly in the phosphosilicate fiber. The investigation of the laser parameters, mathematical simulations and optimization of the Raman laser were carried out. As a result of optimization the 1.24 micrometers output power of 2.4 W was reached at the neodymium fiber laser pump power of 3.6 W, that corresponds to the Raman laser quantum efficiency of 77%.

Radiation resistance of optical fibres with fluorine-doped silica cladding

Spectra and kinetics of decay of (gamma) -irradiation induced loss in optical fibers with pure silica and Ge- and/or F-doped silica core and F-doped cladding made by MCVD and SPCVD methods were measured at room temperature. Induced loss in short-wavelength range is shown to decrease at Ge-content decrease and at F addition to the core glass. Minimum of induced loss is located in long-wavelength range, the best result (about 2 dB/km after the dose 10 kGy) being achieved on pure silica core MCVD fiber. Induced absorption band at 630 nm is observed in pure silica core fibers and it is suppressed by F-doping of the core glass.