Scaling of average power in sub-MW peak power Yb-doped tapered fiber picosecond pulse amplifiers.

Prospects for average power scaling of sub-MW output peak power picosecond fiber lasers by utilization of a Yb-doped tapered fiber at the final amplification stage were studied. In this paper, it was shown experimentally that a tapered fiber allows the achievement of an average power level of 150 W (limited by the available pump power) with a peak power of 0.74 MW for 22 ps pulses with no signs of transverse mode instability.

Radial distribution and absorption cross section of active centers in bismuth-doped phosphosilicate fibers.

Determination of the active centers distribution across the fiber core as well as calculation of absorption cross sections is a challenging task for all types of bismuth-doped fibers. This is due to the low concentration of active centers and the ability of the bismuth ions to form various centers in silica-based glasses. In this work, we demonstrate the results of experimental measurement of radial distribution of bismuth active centers associated with phosphorus in fiber core using the luminescence spectroscopy.

Compact and efficient O-band bismuth-doped phosphosilicate fiber amplifier for fiber-optic communications.

During last decades there has been considerable interest in developing a fiber amplifier for the 1.3-[Formula: see text]m spectral region that is comparable in performance to the Er-doped fiber amplifier operating near 1.55 [Formula: see text]m.

Bend-insensitive bismuth-doped PO-SiO glass core fiber for a compact O-band amplifier.

For the first time, we report on the fabrication of a bend-insensitive single-mode bismuth (Bi)-doped $ {{\rm P}_2}{{\rm O}_5} {-} {{\rm SiO}_2} $PO-SiO fiber having a depressed cladding design and study its gain characteristics at a spectral region of 1.3-1.4 µm.

High-order mode suppression in double-clad optical fibers by adding absorbing inclusions.

We proposed and experimentally demonstrated a technique for the suppression of unwanted modes in double-clad fibers with a high core-to-clad diameter ratio by introducing high-index absorbing inclusions into the first cladding of the fibers. These inclusions disturb the shape of undesirable modes, and a noticeable part of the power becomes localized inside the inclusion, resulting in an increase in the propagation loss of these modes. Two fiber designs were studied and realized: one with cylindrical symmetry and an absorbing high-index ring as the inclusion and another with high-index absorbing rods inserted around the fiber core.

Photostability of laser-active centers in bismuth-doped GeO-SiO glass fibers under pumping at 1550 nm.

We report experimental measurements and numerical calculations regarding the photostability of laser-active centers associated with bismuth (BACs) in Bi-doped GeO-SiO glass fibers under pumping at 1550 nm at different temperatures. It was discovered that BACs are unstable under 1550-nm pumping when the temperature is elevated to hundreds of degrees centigrade. A simple numerical model was proposed to account for the discovered instability which turned out to be in good agreement with the experimental data.

Formation of laser-active centers in bismuth-doped high-germania silica fibers by thermal treatment.

The effect of thermal annealing on the luminescent and laser properties of high-germania-core silicate fibers doped with bismuth was investigated. We studied the behavior of optical absorption assigned to the bismuth-related active centers associated with germanium as well as the behavior of unsaturable absorption in annealed fibers with respect to the Bi content. The dependence of the increment of the active center content on the Bi concentration in the annealed fibers was obtained.

Sub-MW peak power diffraction-limited chirped-pulse monolithic Yb-doped tapered fiber amplifier.

We demonstrate a novel amplification regime in a counter-pumped, relatively long (2 meters), large mode area, highly Yb-doped and polarization-maintaining tapered fiber, which offers a high peak power directly from the amplifier. The main feature of this regime is that the amplifying signal propagates through a thin part of the tapered fiber without amplification and experiences an extremely high gain in the thick part of the tapered fiber, where most of the pump power is absorbed. In this regime, we have demonstrated 8 ps pulse amplification to a peak power of up to 0.

A 23-dB bismuth-doped optical fiber amplifier for a 1700-nm band.

It is now almost twenty-five years since the first Erbium-Doped Fiber Amplifier (EDFA) was demonstrated. Currently, the EDFA is one of the most important elements widely used in different kinds of fiber-optic communication systems. However, driven by a constantly increasing demand, the network traffic, growing exponentially over decades, will lead to the overload of these systems ("capacity crunch") because the operation of the EDFA is limited to a spectral region of 1530-1610 nm.

Photobleaching effect in bismuth-doped germanosilicate fibers.

Photoinduced reduction of absorption (photobleaching) in bismuth-doped germanosilicate fibers irradiated with 532-nm laser has been observed for the first time. It was demonstrated that bismuth-related active centers having the absorption bands at wavelengths of 1400 and 1700 nm degrade under photoexcitation at 532 nm. The photobleaching process rate was estimated using conventional stretched exponential technique.

Prediction of organ toxicity endpoints by QSAR modeling based on precise chemical-histopathology annotations.

The ability to accurately predict the toxicity of drug candidates from their chemical structure is critical for guiding experimental drug discovery toward safer medicines. Under the guidance of the MetaTox consortium (Thomson Reuters, CA, USA), which comprised toxicologists from the pharmaceutical industry and government agencies, we created a comprehensive ontology of toxic pathologies for 19 organs, classifying pathology terms by pathology type and functional organ substructure. By manual annotation of full-text research articles, the ontology was populated with chemical compounds causing specific histopathologies.

Luminescence and optical gain in Pb-doped silica-based optical fibers.

IR luminescence and optical gain in a Pb-doped fiber have been observed for the first time. Absorption, luminescence and pump on/pump off optical gain spectra, as well as luminescence decay time, have been measured in these fibers. Comparison of optical active center characteristics in Pb-doped and Bi-doped fibers of the same composition indicates an essential difference of optical active centers in these two types of fibers.

A comprehensive functional analysis of tissue specificity of human gene expression.

Background: In recent years, the maturation of microarray technology has allowed the genome-wide analysis of gene expression patterns to identify tissue-specific and ubiquitously expressed ('housekeeping') genes. We have performed a functional and topological analysis of housekeeping and tissue-specific networks to identify universally necessary biological processes, and those unique to or characteristic of particular tissues.

Results: We measured whole genome expression in 31 human tissues, identifying 2374 housekeeping genes expressed in all tissues, and genes uniquely expressed in each tissue.

Bi-doped fiber lasers and amplifiers for a spectral region of 1300-1470 nm.

Bismuth-doped fiber lasers operating in the range 1300-1470 nm have been demonstrated for the first time, to our knowledge. It has been shown that Bi-doped alumina-free phosphogermanosilicate fibers reveal optical gain in a wavelength range of 1240-1485 nm with pumping at 1205, 1230, or 808 nm.