Abstract: To improve the efficiency and to reduce the temperature rise of a surface emitting semiconductor laser, the laser includes between a buried active layer and a mirror, a current blocking layer incorporating an opening centered on the active layer and having dimensions less than those of the latter. Applications include optical telecommunication systems.

Abstract: An optical filter is formed by writing at least one long-period Bragg array into an optical fiber which is tapered to define two substantially adiabatic transition areas delimiting an intermediate area in which the long-period Bragg grating is written to produce codirectional coupling between two guided modes in the intermediate area at a wavelength that is a function of the period of the grating.

Abstract: A method of extracting a contour of a contrasted area in a digitized image made up of pixels having different intensity levels defining the contrasted area is based on minimizing the energy of an initial active contour to which are applied stresses derived from a potential image obtained by processing the image. The potential image is obtained from a multifractal analysis of the image so that each element of the potential image is representative of a local fractal dimension in the locality of a corresponding pixel in the image. This improves the behavior of the active contour when it is deformed by the stresses.

Abstract: An apparatus for operating a multiple-stand mill train is described which significantly reduces the expense and time for designing, testing and the start-up, including the optimization phase, and for restarting the roll operation of the mill train and which makes it possible to safely train the operators during operation and to extend the functionality of the mill train without creating damage. For this purpose, the entire mill train is simulated by a single physical simulation model (2) in a structured approach based on the technological interrelationship between the individual stands. The simulation model (2) is connected to a central control apparatus (1), wherein the apparatus alone provides the entire control of the mill train and optionally controls individual functions within each of the stands or of individual stands either via actuating members of the mill train or in corresponding units of the simulator model (2).

Abstract: Digital filters are used to simulate the transmission function of a real system by means of echo cancellers, where a high-speed digital signal processor with a large memory is needed to compute and update the filter coefficients. To reduce the cost of the echo canceller, an autocorrelation, i.e. the correlation of a block of a defined number of sampling values of the transmitted signal with received echoes derived from this transmitted signal, is used by the invention to determine the time periods at which an echo arrives, and at which an update of the filter coefficients then takes place. In this way the number of filter coefficients to be computed and the cost of their computation are significantly reduced, so that echo cancellers for telephone terminals can be produced in a cost-effective manner.

Abstract: An optical communication system is described wherein a center (1) and distant terminals (3, 4) are connected to a fiber-optic network (2). Each of the terminals (3, 4) has a light source (5, 7) and a modulator (6, 8) connected thereto for transmitting optical signals to the center (1). Each of the modulators (6, 8) controls the respective light source (5, 7) in such a way that the light source (5, 7) emits light only within successive first time intervals T.sub.1L, T.sub.2L which are separated by second time intervals T.sub.1D, T.sub.2D and that the first time intervals T.sub.1L, T.sub.2L are shorter than the second time intervals T.sub.1D, T.sub.2D.

Abstract: Comprising one or more resonant cavities in which are produced two resonant modes at two different frequencies f.sub.1 and f.sub.2, both modes having essentially the same field distributions but rotated 90.degree. with respect to each other. Each cavity comprises a tuning element (TS.sub.a) for tuning the resonant frequency f.sub.1 of the first mode along a first axis, a tuning element (TS.sub.b) for tuning the resonant frequency f.sub.2 of the second mode along a second axis perpendicular to the first, input coupling means (IC) and output coupling means (OC) for injecting into and extracting from the cavity, respectively, a radiofrequency signal along axes not parallel to those of resonance. Filter tuning is done by using only two tuning elements, which means that the filter cost is lower and the tuning time is reduced.

Abstract: An optical receiver is presented, which can receive and evaluate an optical signal (S) containing interference caused by polarization mode dispersion (PMD). The optical receiver has a splitting facility (1.1) which splits the routable optical signal (S) into two electrical signal components (S.sub.-, S.sub.+). The electrical signal components (S.sub.-, S.sub.+) are processed in an equalizing circuit (1.2). A control facility (1.3) controls the splitting facility (1.1) with the aid of a quality signal (Q) produced by the equalizing circuit (1.2).

Abstract: A spacer is indicated for a high-frequency coaxial cable with an inner conductor, a tube-shaped outer conductor and a dielectric cavity located between the two conductors which, through the use of different materials, has a higher thermal load capacity in the inner conductor area than in the outer conductor area. When installed, the parts, which are composed of different materials and are superimposed in the radial direction, are mechanically interconnected.

Abstract: A spacer is indicated for a high-frequency coaxial cable with an inner conductor, a tube-shaped outer conductor and a dielectric cavity located between the two conductors, which has a higher thermal load-carrying capacity in the inner conductor area than in the outer conductor area, due to the use of different materials. The parts of the spacer which are made of different materials are radially superimposed and are solidly interlocked with each other by means of injection molding.

Abstract: An optical frequency-encoded CDMA transmission system is presented in which received optical signals are decoded in the electric part of an optical receiver (12). To that end, the optical receiver (12) has a single photodetector (6) which converts received light into an electric signal, and which is directly or indirectly connected to a decoding unit (9, 10; 13, 14, 15), for recovering the information contained in the characteristic frequency-encoded spectrum.

Abstract: A method of fabricating a fluoride glass optical fiber preform which has a fluoride glass core surrounded by a fluoride glass optical cladding includes the following steps: introducing the cladding glass in the molten state into a bottom part of a mold having a cylindrical inside cross-section, introducing the core glass in the molten state into a top part of the mold above the cladding glass, and inwardly solidifying the core glass and the cladding glass from the interface between the glasses and the mold. The kinetics of solidification of the core glass are such that complete solidification of the cladding glass occurs before complete solidification of the core glass.

Abstract: To shape binary optical signals, the apparatus comprises a first stage for providing a modulating signal whose high levels are stabilized so as to depend little on fluctuations in the input signal. The signal is applied to a second stage including an interferometer structure designed to deliver an output signal that is the result of interference between first and second auxiliary waves, the interference being respectively constructive and destructive when the power of the modulating signal corresponds respectively to a first logic state and to a second logic state. The apparatus can be used to modify the input signal by deleting or inserting data. It can be used in optical data switching or transmission.

Abstract: A method of preparing faces of a laser based on III-IV compounds, the method comprising the following operations:1) the faces of the laser are opened;2) said faces of the laser are placed in an enclosure in which there obtains a pressure of about 10.sup.-7 mbar to about 10.sup.-8 mbar, and they are subjected to a step of cleaning by irradiation with a pulsed laser; and3) the same pulsed laser is used to ablate a target so as to subject said faces to a passivation operation whereby silicon Si or gallium nitride GaN is deposited thereon by the pulsed laser deposition method until a thickness is obtained lying in the range 2 .ANG. to 20 .ANG..

Abstract: Apparatus and method for controlling the electromagnetic torque of an asynchronous machine. The apparatus includes a corrector which controls the electromagnetic torque of an asynchronous machine by regulating the magnetic flux and by controlling the electromagnetic torque C.sub.m, the corrector including a regulator circuit (3) for regulating the rotor magnetic flux .phi..sub.r , having non-linear control using input/output linearization by static looping and whose output controls the d-component of the stator current i.sub.s, a first linear corrector (1) of the proportional, integral type whose output v is the input to the regulator circuit, and a second linear corrector (2) of the proportional, integral type whose output controls the angular frequency of the rotor currents .omega..sub.s1.

Abstract: The method is used in a switching network over which data packets are transferred and which includes a plurality of switching nodes with switching node terminations (SNT) and associates in each one of the switching node terminations (SNT) internal header information (IHI) included in an internal data packet received by the switching node termination and identifying an internal connection within the switching node and ending in the switching node termination, to external header information (EHI) included in an external data packet and identifying an outgoing external connection external to the switching node and originating from the switching node termination. The internal header information (IHI) includes a connection reference number (CRN) and a transfer type is associated to the internal connection. The method comprises three steps:a. determining the transfer type;b.

Abstract: A system for writing a Bragg grating point-by-point in an optical waveguide includes an illumination system for producing a primary beam. It further includes a diffraction grating to receive the primary beam and to produce a zero order secondary beam and two symmetrical secondary beams of higher order and a focusing optical device for focusing the secondary beams onto a writing area of the waveguide. The diffraction grating and the focusing optical device define an intensity function of writing in the area of the guide including a central peak and two secondary peaks spaced from the central peak by a distance equal to the pitch of the grating.

Abstract: The control path of the switch (I) comprises an input stage (T2, T1) having an input (H) coupled to the input (E) for the control signal and having its output coupled to the control electrode (G) of the switch (I). A protection circuit (D1, Z2) coupled between the load (C) and the control path includes a threshold effect component (Z2) and a decoupling element (D1). On being made conductive by the current that results from a surge generated in a circuit of the load (C), the protection circuit (D1, Z2) is coupled to the input (H) of said input stage (T2, T1) to act on said switch (I) in the same way as a control signal for the switch (I). In this manner, the control path prevents current in the load (C) from dropping off suddenly.

Abstract: The demultiplexer comprises a diffraction space defined by a reception surface coupled to a grating. In order to obtain output waves of flattened spectral response, the input waveguide and the reception surface are dimensioned so that the input wave diffracts over said surface and presents a plurality of secondary lobes. The demultiplexer is particularly applicable to optical communications systems with wavelength multiplexing.

Abstract: In a method of fabricating a surface emitting semiconductor layer, to achieve good electrical confinement and good flatness of the mirrors delimiting the resonant cavity of the laser, an electrical confinement layer is made by growing a localized aluminum alloy layer on the active layer, except for an opening area on top of which the mirror is to be formed. After epitaxial regrowth, the alloy layer is oxidized laterally. Applications include the fabrication of semiconductor lasers on III-V substrates such as InP and GaAs.