Affordable Developing Country Server/Workstation Network

We propose a method to provide people of low income in developing countries access to sufficiently current personal computing luxuries.Ope

Single-polarization, dual-wavelength mode-locked Yb-doped fiber laser by a 45°-tilted fiber grating

We experimentally demonstrate an all-fiber single-polarization dual-wavelength Yb-doped fiber laser passively mode-locked with a 45°-tilted fiber grating for the first time. Stable dual-wavelength operation exhibits double-rectangular spectral profile centered at 1033 and 1053 nm, respectively. The 3 dB bandwidth of each rectangular optical spectrum is estimated as 10 nm. The separation of two fundamental repetition rates is 6 kHz. By employing the 45° TFG with the polarization-dependent loss of 33 dB, output pulses with 27 dB polarization extinction ratio are implemented in the experiment. The single pulse centered at 1053 nm is researched by using a filter at the output port of the laser, and the experimental results denote that the output ps pulses are highly chirped. The formation mechanism of dual-wavelength operation is investigated

Microprocessor based prototyping system for inverters control system testing

Microprocessor based system for testing the controllers of converters is presented in the paper. The system is useful for testing control systems and control algorithms or for parameterization of controller. During the tests of the new controller of converter it is not reasonable use real converter and real controlled object because of possibility of damage. The idea of presented system is using instead the real elements its models based on microcontroller with short computation time that ensures feedback signal for control systems and emulates operation of real converter and controlled object. Presented microprocessor based rapid control prototyping system can emulate operations of two level converter with induction motor or two level active front end converter with the grid. The idea and practical realization of proposed system and emulated controlled object are described in the paper. The features, operation and parameterization of proposed microprocessor based rapid control prototyping system are presented. Proper operation of proposed system is proved by results of experimental tests achieved with laboratory control system operating with scalar and vector control and laboratory active front end controller. The possibility of checking influence of selected disturbances (for example voltage harmonics) is also presented.W artykule przedstawiono mikroprocesorowy system służący do prototypowania układów sterowania przekształtników. Jest on przydatny przy testowaniu układów sterowania, algorytmów sterowania oraz doborze parametrów sterowników przekształtników. Idea opisywanego systemu polega na wykorzystaniu do modelowania obiektu regulacji mikrokontrolera o dużej szybkości działania, oprogramowanego w ten sposób aby modelować z wystarczającą dokładnością zachowanie obiektu. System prototypowania powinien dostarczać wymaganych sygnałów sprzężeń zwrotnych dla badanego sterownika. Opracowany mikroprocesorowy system prototypowania modeluje pracę przekształtnika dwupoziomowego z silnikiem indukcyjnym klatkowym lub przekształtnika dwupoziomowego współpracującego z siecią zasilającą. W artykule opisano ideę i realizację systemu prototypowania oraz utworzone modele obiektów regulacji. Omówiono działanie i właściwości wykorzystanego systemu mikroprocesorowego i programu do parametryzacji modeli. Działanie mikroprocesorowego systemu prototypowania zostało potwierdzone wynikami laboratoryjnymi uzyskanymi przy testowania sterownika falownika silnika przy sterowaniu skalarnym i polowo-zorientowanym oraz przy testowaniu algorytmu sterowania przekształtnikiem sieciowym. Przedstawiono również możliwości badania zjawisk zakłóceniowych, np. związanych z występowaniem odkształceń napięcia w modelu sieci zasilającej

Sub-picosecond Graphene-based Harmonically Mode-Locked Fiber Laser With Repetition Rates up to 2.22 GHz

Passive harmonic-mode locking (PHML) of erbium-doped fiber laser with multilayer graphene is presented. The laser could operate at several harmonics (from 2nd to 21st) of the fundamental repetition frequency of the ring resonator (106 MHz). The highest achieved repetition rate was 2.22 GHz (which corresponds to the 21st harmonic) with 900 fs pulse duration and 50 dB of the supermode noise suppression. The saturable absorber was formed by multilayer graphene, mechanically exfoliated from pure graphite block through Scotch-tape and deposited on the fiber ferrule

Fiber-MOPA sources of coherent radiation

This paper presents the concept and design of medium to high power fiber radiation sources in MOPA (Master Oscillator Power Amplifier) configuration. Research results are presented on a two-stage power amplifier for MOPA applications for the third telecommunications window at 1550 nm based on active erbium-doped and erbium/ytterbium-doped fibers. The amplifier is fabricated entirely in fiber technology and delivers several watts of output power

A graphene-based mode-locked nano-engineered zirconia-yttria-aluminosilicate glass-based erbium-doped fiber laser

We demonstrate a simple, compact and low cost graphene-based mode-locked nano-engineered erbium-doped zirconia-yttria-aluminosilicate (ZYA-EDF) glass-based fiber laser. The fiber preform in a quaternary glass host of silica-zirconia-yttria-aluminum was made through the modified chemical vapor deposition (MCVD) process followed by the solution doping technique. The core glass is made of 0.40 mol% of Al2O3, 3.0 mol% of ZrO2 and 0.25 mol% of Er2O3, which give rise to a peak absorption of 30.0 dB m(-1) at 978 nm and a fluorescence lifetime of 10.65 ms. Such a doping host provides the high concentration of erbium ions of 4500 ppm without any clustering. Such an active fiber was used as a gain medium for an ultra-fast femtosecond fiber laser, mode locked by a graphene oxide (GO) saturable absorber. This paper describes geometrical and optical characterization of the nano-engineered glass-based erbium-doped optical fiber (ZYA-EDF) as well as the performance of the mode-locked femtosecond laser based on the developed fiber. The all-anomalous cavity laser generated soliton pulses with 8.5 nm bandwidth, 50 MHz repetition frequency and nearly transform-limited 400 fs duration at 1561 nm center wavelength using a new class of EDF

Synthesis and Characterization of Antimony Telluride for Thermoelectric and Optoelectronic Applications

Antimony telluride (Sb2 Te3 ) is an intermetallic compound crystallizing in a hexagonal lattice with R-3m space group. It creates a c lose packed structure of an ABCABC type. As intrinsic semiconductor characterized by excellent electrical properties, Sb2 Te3 is widely used as a low-temperature thermoelectric material. At the same time, due to unusual properties (strictly connected with the structure), antimony telluride exhibits nonlinear optical properties, including saturable absorption. Nanostructurization, elemental doping and possibilities of synthesis Sb2 Te3 in various forms (polycrystalline, single crystal or thin film) are the most promising methods for improving thermoelectric properties of Sb2Te3.Applications of Sb2 Te3 in optical devices (e.g. nonlinear modulator, in particular saturable absorbers for ultrafast lasers) are also interesting. The antimony telluride in form of bulk polycrystals and layers for thermoelectric and optoelectronic applications respectively were used. For optical applications thin layers of the material were formed and studied. Synthesis and structural characterization of Sb2 Te3 were also presented here. The anisotropy (packed structure) and its influence on thermoelectric properties have been performed. Furthermore, preparation and characterization of Sb2 Te3 thin films for optical uses have been also made

Passively synchronized Q-switched and mode-locked dual-band Tm3+:ZBLAN fiber lasers using a common graphene saturable absorber

Dual-band fiber lasers are emerging as a promising technology to penetrate new industrial and medical applications from their dual-band properties, in addition to providing compactness and environmental robustness from the waveguide structure. Here, we demonstrate the use of a common graphene saturable absorber and a single gain medium (Tm(3+):ZBLAN fiber) to implement (1) a dual-band fiber ring laser with synchronized Q-switched pulses at wavelengths of 1480 nm and 1840 nm, and (2) a dual-band fiber linear laser with synchronized mode-locked pulses at wavelengths of 1480 nm and 1845 nm. Q-switched operation at 1480 nm and 1840 nm is achieved with a synchronized repetition rate from 20 kHz to 40.5 kHz. For synchronous mode-locked operation, pulses with full-width at half maximum durations of 610 fs and 1.68 ps at wavelengths of 1480 nm and 1845 nm, respectively, are obtained at a repetition rate of 12.3 MHz. These dual-band pulsed sources with an ultra-broadband wavelength separation of ~360 nm will add new capabilities in applications including optical sensing, spectroscopy, and communications