Multichannel equalised and stabilised gain amplifier for WDMtransmissions

The authors present a new type of optical amplifier for WDM systems. A theoretical comparison between transmission lines using either a conventional stabilised flattened gain amplifier or the proposed multichannel equalised and stabilised gain amplifier shows that the latter can improve WDM transmissions     

Behavior of Bragg gratings, written in germanosilicate fibers,against γ-ray exposure at low dose rate

Bragg gratings have been written within four germanosilicate fibers either by a pulsed or by a continuous-wave exposure of each fiber to a coherent UV two-beam interference pattern. These gratings have been exposed under steady state conditions to γ-ray doses as high as 10 ⁴ Grays. The dose rates ranged between 10 Gy/h and 1.3×10² Gy/h. The transmission spectra of the fibers have been recorded during and after the ⁶⁰Co irradiation, near the grating Bragg wavelengths. Whereas the induced loss reached 600 dB/km near 1.3 μm, no significant change in the spectral characteristics of the gratings could be detected within the experimental accuracy, enabling their future use in a nuclear environment     

Au delà d’une vitesse de groupe: vitesse d’onde et vitesse de signal

A radiated fieldalways appears in a dual, spatial and temporal, aspect. Its spatial one is the wave the author should observe at a given time. Its temporal one is the signalhe receive at a given point. The aim of this paper is then to determine bulk velocities of both signal and wave — without any limiting assumption on their spectral widths — in case the field is being radiated thru a dispersive medium. A realistic criterion is first adopted that enables an accurate measurement of the instant position of the wave, by means of a definite space-marker (the wave center. The same criterion also leads to a similar timemarker (the signal center,) that will be used in measuring the receiving time of the signal. By studying the motion of these markers, an operator U spontaneously appears beside the phase velocity This operator has the same analytical expression as the usual group/signal velocity of a wave packet. Therefore U should be also called group velocity. Both group and phase velocities depend on the transmitting medium only. To the travelling wave then corresponds an uniform motion of its wave center, with some wave velocity. The latter consists of the mean of operator U in a state which is associated with the wave structure at the time origin. To the signal, when received by a fixed transductor, also corresponds some signal velocity. Its value is the inverse of the mean of operator U ^?1 in a state which is associated with the signal structure at the transmitter. Thus, wave velocity and signal velocity not only depend on the transmitting medium, but depend on the emitted signal form too. However both of them become identified with the group velocity U in the particular case of a very narrow spectrum. Thus agreeing with the usual wave packet. In such a case the group velocity turns out to be the velocity of the very marker that belongs to the amplitude of the transmitted analytic signal. Such an approach also enables us to describe signal distortion in a dispersive medium. By analogy, it leads to relating that distortion to Fresnel diffraction. Outside anomalous zones, the above properties are roughly maintened when attenuation is taken into account in relation to dispersion.     

Pretreatment and cleaning of hyperfiltration (reverse osmosis) membranes in municipal wastewater renovation

Membrane fouling is a common cause of poor performance in hyperfiltration systems especially when treating wastewaters usually because it reduces the product flux to uneconomical levels. In the present paper various membrane cleaning methods are reviewed and related factors affecting process performance such as pretreatment, system geometry and membrane choice are discussed. Several leads in developing new membrane cleaning and pretreatment methods are also presented.     

Cathodic behaviour of p-toluenesulfonamides in organic solvents

Cathodic reduction of several secondary and tertiary p-toluenesulfonamides and gem-N-disulfonamides were investigated by cyclic voltammetry and controlled potential electrolysis at mercury electrode in aprotic and protic dmf. In the cleavage of tertiary p-toluenesulfonamides two Faradays per mole were consummed, resulting in the formation of amine and the sulfinate ion. In the case of secondary p-toluenesulfonamides, electrochemically inactive sulfonamide anions were formed at the electrode surface by acid–base reaction between acidic substrate and electrogenerated bases. Sulfonamides anions were obtained also in the solution bulk with adding strong base and by cathodic cleavage of gem-N-disulfonamides in aprotic media. General reduction mechanisms are postulated and structure effects on the scope of the reduction are discussed for more complex sulfonamides.     

Reduction electrochimique de propene nitriles substitues—III alkyl(aryl)oxy-3 phenyl-3 propene nitriles Z et E

The preparation and the separation of E- and Z-isomers of 3-alkyl(aryl)oxy-3-phenylpropenenitriles are described. Configurations are assigned by nmr.In aqueous-organic media Z-isomers are more easily reduced than E-isomers. In anhydrous acetonitrile differences between E$\text{1}\text{2}$ of E- and Z-isomers are smaller or null.Polarography, cyclic voltammetry and macro-scale reductions with identification of products permit us to propose a reduction mechanism. If Taft's constant σ* of R group is negative the CC double bond is reduced with formation of 3-alkyl(aryl)oxy-3-phenylpropanenitriles. If σ* is positive the intermediate radical-anion loses RO^? ion; cinnamonitrile is formed but immediately reduced, either to in 3-phenylpropanenitrile, or to in 3,4-diphenylhexane dinitrile.It is possible to get hydrodimers while conserving OR group.     

Pump wavelength optimisation of erbium-doped fibre amplifier in 800 nm band

The absorption band centred around 805 nm suffers from two excited state absorption (ESA) bands which peak, respectively, at 790 nm. The difficulty in comparing the pump wavelength efficiencies comes from the fact that the optimum amplifier length depends not only on pump power but also on pump wavelength. It is shown that for high pump powers, pumping around 820 nm is most efficient, however for lower pump powers shorter wavelengths provide the highest gains.<>     

Formation pratique à la conception d’un circuit intégré spécifique

We present an example of practical works in design methodology for realizing digitalASIC circuit, at the graduate level in the microelectronics engineering program (ISIM) of the University of Montpellier II. This training program is illustrated by the design of a small project from specification to silicon manufacturing files, using a CMOS standard cell approach with theCAD softwares system Hilo (Genrad) and Solo 1400(ES2).