I. A. Bufetov

Bismuth-doped-glass optical fibers—a new active medium for lasers and amplifiers

Optical fibers with bismuth-doped silicate and germanate glass cores were fabricated by the modified chemical vapor deposition technique (solution and vapor-phase Bi incorporation). The fibers revealed an efficient luminescence with a maximum in the 1050-1200 nm spectral range, FWHM up to 200 nm, and a lifetime of the order of 1 ms.

Combined excitation-emission spectroscopy of bismuth active centers in optical fibers

3D excitation-emission luminescence spectra of Bi-doped optical fibers of various compositions were measured in a wide wavelength range 450-1700 nm. Such luminescence spectra were obtained for Bi-doped pure silica and germania fibers, and for Bi-doped Al- or P-codoped silica fibers (at room and liquid nitrogen temperatures). The energy level schemes of IR bismuth active centers in pure silica and germania core fibers were derived from spectra obtained. The energy level schemes similarity of bismuth active centers in these two types of fibers was revealed.For the first time, 3-dimensional luminescence spectra (luminescence intensity as a function of the excitation and emission wavelengths) have been obtained for bismuth-doped optical fibers of various compositions in a wide spectral range (450-1700 nm). The bismuth-doped fibers investigated have the following core compositions: SiO(2), GeO(2), Al-doped SiO(2), and P-doped SiO(2). The measurements are performed at room and liquid nitrogen temperatures. Based on the experimental results, the positions of the low-lying energy-levels of the IR bismuth active centers in SiO(2)- and GeO(2)-core fibers have been determined. Similarity of the energy-level schemes for the two core compositions has been revealed.

Laser diode pumped bismuth-doped optical fiber amplifier for 1430 nm band

A 24 dB gain bismuth-doped fiber amplifier at 1430 nm pumped by a 65 mW commercial laser diode at 1310 nm is reported for the first time (to our knowledge). A 3 dB bandwidth of about 40 nm, a noise figure of 6 dB, and a power conversion efficiency of about 60% are demonstrated. The temperature behavior of the gain spectrum is examined.

Germania-glass-core silica-glass-cladding modified chemical-vapor deposition optical fibers: optical losses, photorefractivity, and Raman amplification

Germania-glass-core silica-glass-cladding single-mode fibers (deltan as great as 0.143) with a minimum loss of 20 dB/km at 1.85 microm were fabricated by modified chemical-vapor deposition. The fibers exhibit strong photorefractivity, with type IIa index modulation of 2 x 10(-3). A Raman gain of 300 dB/(kmW) was determined at 1.12 microm. Only 3 m of such fibers is sufficient for constructing the 10-W Raman laser at 1.12 microm with a 13-W pump at 1.07 microm.

Bismuth-doped silica-based fiber lasers operating between 1389 and 1538 nm with output power of up to 22 W

An efficient CW bismuth fiber laser operating around 1.46 μm with an efficiency of >50% and an output power of >20 W has been developed on a bismuth-doped GeO(2)-SiO(2) fiber. The laser demonstrates weak dependence of the output power on temperature in comparison with bismuth lasers operating near 1.15 and 1.3 μm. The laser generation has been obtained in the range 1.39 to 1.54 μm. The first linearly polarized bismuth-doped fiber laser at 1.46 μm based on a PANDA-type fiber has been demonstrated.

Ultraviolet-light generation in nitrogen-doped silica fiber

Nonlinear light transformations were observed in a nitrogen-doped silica fiber pumped with a Nd:YAG laser (lambda=1.06 microm) . Light generation in the spectral range 355-430nm was obtained with an efficiency of up to 2x10(-4) . The UV light was found to be the result of third-harmonic generation, stimulated Raman scattering of the third harmonic, and third-harmonic generation from the Stokes components of the pump light. Lasing based on the color centers of nitrogen-doped silica was observed in the range 380-430nm.

CW highly efficient 1.24 /spl mu/m Raman laser based on low-loss phosphosilicate fiber

We report the first demonstration of an extremely simple and efficient 1.24 /spl mu/m phosphosilicate fiber-based Raman laser with Bragg gratings written directly in the fiber used. The laser pumped by Nd fiber laser exhibits a slope efficiency of 80%.

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.

Time-resolved spectroscopy and optical gain of silica-based fibers co-doped with Bi, Al and/or Ge, P, and Ti

The optical properties of optical fibers based on silica glass doped with bismuth and co-doped with aluminum oxides and/or germanium, phosphorus, and titanium oxides are studied. The optical loss and luminescence spectra of optical fibers substantially depend on the core composition. The gain spectra of single-mode optical fibers are measured in the IR range. It is demonstrated that the phosphorus-germanium-silicate optical fiber doped with bismuth exhibits a broad gain band (1270–1520 nm) when pumped at a wavelength of 1230 nm. It is also shown that the bismuth-aluminosilicate optical fibers additionally doped with Ge or Ti at about 1 at % have the gain spectra that are significantly narrower than the IR luminescence spectra (in contrast to the fibers that do not contain Ge and Ti). The intensity decay curves of the IR luminescence in such fibers indicate the presence of both short-lived (with the lifetime τ≤4 μs) and long-lived (τ ∼ 1 ms) energy levels in the bismuth active centers.

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%.