Abstract: A method of selectively compensating for the chromatic dispersion of optical signals in an optical telecommunication network, comprising the steps of transmitting at least two signals over a common portion of said network, separating at least one of the signals from the remaining signals at at least one point of the network, compensating for the chromatic dispersion of this signal and recombining said signal with the remaining signals at said one point of the network. Preferably this method further comprises the steps of detecting the chromatic dispersion of each of the signals at at least one point of the network, identifying, among the signals, the signals to be compensated, for which the detected dispersion value does not fall within a range of predetermined values and compensating for the dispersion of said signals so as to make them fall within this range of predetermined values.

Abstract: An optical self-healing-ring communication network is described which include: a first optical communication line, forming a closed optical path; at least two add/drop nodes for optical signals, optically connected along the line; a second optical communication line forming a closed optical path and optically connected to the optical-signal add/drop nodes. Defined in the network are first and second mutually opposite travel directions of the optical signals, with respect to the position of the optical-signal add/drop nodes. At least one of said nodes further comprises selection means, controlled by the optical signals, for the selective dropping of the optical signals from one of the communication lines. At least one of the optical-signal add/drop nodes further include means for the simultaneous input of at least one optical signal in the first direction along the first communication line and in the second direction along the second communication line.

Abstract: An optical telecommunication system including a transmitting station and a receiving station for optical signals, connected with each other by an optical fiber line including optical line amplifiers having a rare-earth-doped active fiber and connected in series, in which the transmitting station includes signal generator for generating signals at several wavelengths, and connections for conveying the signals to a single optical fiber line. The optical signal receiving station includes apparatus for separating the signals. At least one of the optical line amplifiers has dopants, fiber length and pumping power capable of determining, at the input of the receiving station, an optical signal/noise ratio which for the different wavelengths has a difference less than 2 dB, and for each signal is greater than 15 dB.

Abstract: The present invention relates to an optical amplifier and a telecommunication system including a plurality of the optical amplifiers connected in cascade, particularly adapted for a wavelength division multiplexing transmission, in which a combination of dopants in the active fiber core of the optical amplifiers enables a high signal/noise ratio to be achieved for all channels in a predetermined wavelength band, even in the presence of several simultaneously fed signals.

Abstract: An optical telecommunication system has at least two sources of optical modulated signals at different wavelengths in a predetermined transmission wavelength band, together with a multiplexer for the signals, an optical fiber line connected at one end to the multiplexer, and a demultiplexer/receiver for the signals. The line comprises an optical fiber having a chromatic dispersion value lower than a predetermined value in the transmission wavelength band and increasing as wavelength increases. The fiber also has a zero value of chromatic dispersion at a wavelength lower than the minimum wavelength of the transmission wavelength band by such an amount that no local wavelength zero value of the chromatic dispersion present in the fiber and capable of generating a four-wave-mixing phenomenon is included in the band.

Abstract: A multi-wavelength optical telecommunication method includes: generating at least two optical transmission signals of wavelengths different from each other, multiplexing the optical signals in a single transmission fibre, forming a multi-wavelength optical signal, transmitting, through the transmission fibre, the multi-wavelength optical signal including the optical transmission signals to a respective receiving station and separating the optical transmission signals, in which the step of separating the optical transmission signals includes: distributing the received multi-wavelength optical signal onto at least two output fibres; selectively reflecting a wavelength band of the multi-wavelength optical signal including at least one of the optical transmission signals, so that the reflected band propagates over the output fibre in an opposite direction to the multi-wavelength optical signal; separating the reflected band from the output fibre and feeding it, through a receiving fibre, to a respective receiver.

Abstract: The present invention relates to an optical amplifier and a telecommunication system including a plurality of the optical amplifiers connected in cascade, particularly adapted for a wavelength division multiplexing transmission, in which a combination of dopants in the active fiber core of the optical amplifiers enables a high signal/noise ratio to be achieved for all channels in a predetermined wavelength band, even in the presence of several simultaneously fed signals.

Abstract: An optical telecommunication system includes means for generating optical signals of different wavelengths, an optical-fibre line with amplifying means, a pre-amplifer, and receiving means. The the pre-amplifier comprises an optical waveguide doped with a rare earth material, differential-attenuation means located at a first position along the doped waveguide and capable of causing an attenuation in the signal band which is greater than the attenuation caused at the pumping wavelength, and filtering means located at a second position and adapted to attenuate by a value higher than a predetermined minimum, the spontaneous emission in a wavelength band contiguous with the signal band.The position and attenuation of the differential-attenuation means and filtering means and the wavelength band are selected in a functional relation with respect to each other in order to limit the output power variations from the pre-amplifier.

Abstract: An optical telecommunication system includes at least two sources of optical signals modulated at different wavelengths, having respective coherence times; a multiplexer for multiplexing said signals in a single common optical fibre; an optical-fibre line connected at one end to the common optical fibre of the multiplexer; a receiver for receiving said signals; an element for reducing the four wave mixing (FWM) between the signals, optically connected in series along the optical-fibre line. The FWM-reducing element includes an optical circuit including at least two-wavelength-selective filters, each relative to a wavelength band including one of the optical signals. The filters are optically connected in series with each other over an optical path, and the length of at least one section of the optical path included between two consecutive filters is greater than the length corresponding to the coherence time of at least one of the sources of optical signals.

Abstract: An optical fiber power amplifier, particularly for telecommunication lines with optical fibers, including an active fiber doped with Erbium as a fluorescing substance, and with Al.sub.2 O.sub.3 as refraction index modifying dopant. The fiber is pumped with a laser providing a wavelength higher than 520 nm and preferably, 980 nm. The amplifier has a particularly high amplification efficiency close to the theoretical maximum efficiency.

Abstract: An apparatus or "coupler" for use in welding two lengths of pipe to be butt-welded, particularly suitable for welding a section of pipe to the end of a pipeline section being laid on the sea bottom, comprising an elongate body having a first portion and a second portion, which can be attached to respective pipes by means of respective attachment means and sliding means cooperating with the attachment means in order to move the first and second pipes towards each other, whereby, during the welding, not only the two pipes on internally changed to the said portions with their axes aligned, but are also drawn and held together, even when one of the pipes undergoes a longitudinal reciprocating movement.