Timing jitter reduction in gain-switched VCSELs induced by external optical injection

A theoretical study of the effect of optical injection on the characteristics of pulses generated by gain-switched single and multimode VCSELs is performed. It is shown that a jitter reduction greater than 50% can be obtained with a slight increase in pulse width. Similar results are obtained for single and multimode emission when the light is injected in the dominant mode.     

Long-Distance Transmission at Zero Dispersion: Exact Expressions for One-Time Statistical Properties

We study the transmission of a signal through a dispersionless fiber with in-line amplifiers. The nonlinearities of the fiber and the noise generated at each amplifier are taken into account. Exact analytical expressions are obtained for the field averages. From these results we obtain the distributed amplification approximation, and study the conditions under which this approximation is valid.     

Influence of the clay and the nickel content in catalysts for vegetable oil hydrogenation

Nickel catalysts prepared using two different clays as support, natural bentonite and palygorskite, and with different nickel contents have been tested in the hydrogenation of a sunflower oil. The influence of the clays, and of the nickel-bentonite ratio on the activity, selectivity and trans-isomer formation was investigated. Previously it was establised that no diffusional limitations were controlling the rate. Bentonite with the highest nickel content was the most active and selective catalysts.     

Stability of a diode laser with phase-conjugate feedback

An exact analysis is presented of the steady-state stability of a semiconductor laser subjected to feedback from a phase-conjugate mirror. Reduced stability occurs at low feedback whenever the effective external delay time is an integer multiple of the relaxation oscillation period. The role of a finite response time of the mirror is to enhance drastically the steady-state stability.     

Differences Between One Aluminic Palygorskite and Another Magnesic by Infrared Spectroscopy

Two Spanish palygorskites, one from Cáceres (Serradilla) and the other from Segovia (Sacramenia) are studied by means of infrared spectroscopy techniques, both in their natural state and after systematic treatment with hydrochloric acid. The first one is identified as aluminic and the second as magnesic. It is found that the magnesic palygorskite is more easily attacked by the acid.     

Digital key for chaos communication performing time delay concealment

We introduce a scheme that integrates a digital key in a phase-chaos electro-optical delay system for optical chaos communications. A pseudorandom binary sequence (PRBS) is mixed within the chaotic dynamics in a way that a mutual concealment is performed; e.g., the time delay is hidden by the binary sequence, and the PRBS is also masked by the chaos. In addition to bridging the gap between algorithmic symmetric key cryptography and chaos-based analog encoding, the proposed approach is intended to benefit from the complex algebra mixing between a (pseudorandom) Boolean variable, and another continuous time (chaotic) variable. The scheme also provides a large flexibility allowing for easy reconfigurations to communicate securely at a high bit rate between different systems.     

Influence of external hydrogen diffusion on the rate of oil hydrogenation

Experimental data obtained in a Parr reactor for vegetable oil hydrogenation rate using a nickel catalyst supported on clay, with different catalyst to oil ratios and different stirring speeds are used to show the regime of operation and to calculate the contribution of resistance to external hydrogen diffusion to the process rate.     

Preparation of rhodium catalysts on laminar and zeolitic structures by anchoring of organometallic rhodium

Rhodium catalysts supported on six different aluminosilicate structures were prepared by hydrogen reduction of a cationic organometallic rhodium complex anchored to the support. The precursor active phase was incorporated in acetone medium through ion exchange using [Rh(Me₂CO)_x(NBD)]ClO₄ as the metal precursor species, in which NBD is 2,5‐norbornadiene and (Me₂CO)_x is acetone. The effect of the structure and characteristics of the support on metal load and dispersion was studied in the heterogeneous catalysts thus prepared. The supports were characterized by X‐ray diffraction, energy‐dispersive X‐ray analysis, volumetric adsorption and surface acidity. For the precursors and catalysts, the metal load was determined by UV–VIS spectra, the reduction temperature was determined by differential scanning calorimetry, and rhodium dispersion was measured by chemisorption. The structure of the materials used as supports had a great influence on the catalyst prepared. A higher metal content was achieved in the supports with laminar structures, whereas better dispersion was shown by the catalysts supported on zeolitic structures. Copyright © 2001 John Wiley & Sons, Ltd.