Exploiting the short wavelength gain of silica-based thulium-doped fiber amplifiers.

Short wavelength operation (1650-1800 nm) of silica-based thulium-doped fiber amplifiers (TDFAs) is investigated. We report the first demonstration of in-band diode-pumped silica-based TDFAs working in the 1700-1800 nm waveband. Up to 29 dB of small-signal gain is achieved in this spectral region, with an operation wavelength accessible by diode pumping as short as 1710 nm. Further gain extension toward shorter wavelengths is realized in a fiber laser pumped configuration. A silica-based TDFA working in the 1650-1700 nm range with up to 29 dB small-signal gain and noise figure as low as 6.5 dB is presented.

Ultra-short wavelength operation of a thulium fibre laser in the 1660-1750 nm wavelength band.

Ultra-short wavelength operation of a thulium fibre laser is investigated. Through use of core pumping and high feedback efficiency wavelength selection, a continuously-tunable fibre laser source operating from 1660 nm to 1720 nm is demonstrated in a silica host. We discuss the range of applications within this important wavelength band such as polymer materials processing and medical applications targeting characteristic C-H bond resonance peaks. As a demonstration of the power scalability of thulium fibre lasers in this band, fixed wavelength operation at 1726 nm with output power up 12.6 W and with slope efficiency > 60% is also shown.

Diode-pumped wideband thulium-doped fiber amplifiers for optical communications in the 1800 - 2050 nm window.

We present the first in-band diode-pumped TDFAs operating in the 2 µm wavelength region and test their suitability as high performance amplifiers in potential future telecommunication networks. We demonstrate amplification over a 240 nm wide window in the range 1810 - 2050 nm with up to 36 dB gain and noise figure as low as 4.5 dB.

[Computational methods for prediction of structure of membrane proteins using their amino acids sequences].

The structure of membrane proteins is interesting because of their functional properties that are important to medicine and pharmacology. The feature and an organic property of polytopic membrane proteins is the repetition of transmembrane regions consisting of hydrophobic amino acids. The ordered repetition--periodicity--can be identified by the Fourier method, applied to a digital image of symbolic sequence of amino acids in a protein. In this work it was carried out for the 24 transmembrane proteins, for 14 of them successfully. If the repetition of transmembrane regions is ordered insufficiently--non-periodic, then a different method is supposed to use for its detection--the method of multiple (4-5 times) averaging of function of hydrophobicity of the protein within a "window" with width 9-11 aa moved along the sequence. This new method was applied to the same 24 transmembrane proteins (for 19 of them successfully) and it was shown to be more suitable (than the Fourier method) for predicting of the secondary structure of such proteins and functional properties corresponding to it.

Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm.

We describe an efficient Er:YAG laser that is resonantly pumped using continuous-wave (CW) laser diodes at 1470 nm. For CW lasing, it emits 6.1 W at 1645 nm with a slope efficiency of 36%, the highest efficiency reported for an Er:YAG laser that is pumped in this manner. In Q-switched operation, the laser produces diffraction-limited pulses with an average power of 2.5 W at 2 kHz PRF. To our knowledge this is the first Q-switched Er:YAG laser resonantly pumped by CW laser diodes.

[Investigation of periodic distributions of amino acids in the sequences of fiber proteins of bacteriophage T4].

Sequences of amino acids of some fiber proteins may have a periodic structure. To analyze this periodicity Fourier transform of a mathematical image of symbolic sequence of amino acids in a protein is sometimes used. In this work we employed one (out of few possible) particular way of doing Fourier transform as the most straightforward and optimal. Employing this optimal Fourier transform method we analyzed periodicity of fiber proteins in bacteriophage T4. As a result we managed to confirm that a certain periodicity exists in the investigated proteins. It was found that for a number of proteins the alternation of elements of the same group in the amino acid sequence with a rather small period T = 15 exists, whereas for some other proteins alternations have small periods 10 and 8. The new result is a discovery of relatively large periods of amino acids alternations, which divide the amino acids sequence of the protein into 4 or 6 equal parts. These data on the amino acids periodicity allowed us to align amino acids sequences in accordance with the established periods of both types, in agreement with certain results obtained in X-ray crystallography and electron microscopy experiments.