Abstract: The invention relates to a method of reducing the intensity distortion induced by cross phase modulation in a wavelength division multiplexed optical fiber transmission system comprising a transmission line made up of a plurality of optical fiber segments with repeaters interposed between successive optical fiber segments, the transmission system having N different wavelength channels, where N is an integer greater than unity. In each repeater interconnecting first and second consecutive fiber segments, a time offset is introduced between the channels in such a manner that compared with the inlet of the first optical segment, the (n+1)th and the nth channels are offset by &tgr;n at the inlet to the second fiber segment, where n is an integer less than or equal to N, where &tgr;n is selected to be greater than zero and less than a value that eliminates correlation between the intensity distortion contributions of each fiber segment.

Abstract: The present invention propose an optical filter for filtering out at least a part of one of two spectral side-bands of a coded optical signal spectrum having a carrier wavelength, the first of said side-bands which is to be transmitted by said filter being called transmitted side-band the second of said side-bands which is to be filtered out by said filter being called vestigial side-band, said optical filter having a transmission response in intensity, having a maximum value at a central filter wavelength distinct from said carrier wavelength and located in said transmitted side-band, and said response being divided into two parts, a first filter part associated to a wavelength region including said carrier wavelength, a second filter part associated to a wavelength region which does not include said carrier wavelength where at a given value of transmittance distinct from said maximum value, said second filter part has a filter width smaller than the filter width of said first filter part.

Abstract: A wavelength division multiplex optical signal regenerator is inserted between two optical fiber sections of a wavelength division multiplex fiber optic transmission system including a transmission line made up of a plurality of optical fiber sections and providing N channels at different wavelengths where N is an integer greater than 1. The regenerator includes a demultiplexer for demultiplexing wavelength division multiplexed optical signals onto N individual channels, and a multiplexer for multiplexing optical signals at the output of the N individual channels into multiplexed optical signals. Each individual channel includes a saturable absorber for reshaping the optical signals of each channel, and a delay line. The length of each delay line is chosen to introduce a total delay &tgr;n″ between the (n+1)th channel and the nth channel to obtain a time shift of &tgr;n between the (n+1)th channel and the nth channel.

Abstract: The invention provides an optical device for demultiplexing at least two RZ optical signals, each having a distinct non-zero intensity, said signals belonging to a given transmission channel having a given carrier frequency, and the device comprising:

Abstract: The invention relates to an optical fiber transmission system using soliton signals and wavelength division multiplexing. To reduce the effects of collision-induced jitter on the soliton channels, the invention proposes to interchange the wavelengths of the channels of the multiplex at least once, so as to invert the sign of the residual frequency variation induced by the asymmetrical collisions on the signals of the channels. The invention is applicable in particular to transmission systems implementing a frequency allocation scheme that guarantees that the bit times of the various channels are synchronous at regular intervals.

Abstract: The invention relates to apparatus for limiting noise in the “zeros” of optical RZ signals, the apparatus comprising a birefringent fiber for mutually spectrally offsetting the signals as a function of their intensity, and a filter for filtering the offset signals. The filter attenuates the pulses that correspond to “zeros”, but passes the pulses that correspond to “ones”. The invention makes it possible to limit the noise in the “zeros” of an RZ signal.

Abstract: In the invention, a stream (S) of solitons enters a Sagnac interferometer (6) with an offset semiconductor amplifier (A) and the amplifier is controlled by an optical synchronization signal (Y) that is amplitude-modulated at a frequency which is half a bit frequency of the stream, the offset of the amplifier in said interferometer and the parameters of said synchronization signal being given values such that two adjacent solitons of said train are transmitted with their optical phase relationship inverted. The invention finds an application in fiber optic telecommunications networks.

Abstract: The invention shows a frequency allocation scheme for optical channels transmitted via a WDM transmission line with alternating left side and right side filtering for adjacent channels, with alternating channel spacing of A and B, where A<B, and two sets of channels orthogonally polarized.

Abstract: The invention shows a transmission system with a transmitter function, a transmitting fiber and a receiver function where the transmitter function comprising lightsources (1), modulators (2) and a multiplexer (3), and the receiver comprising at least a demultiplexer (5), filters and electrical receivers where the channels for left side filtering are modulated with modulators with a negative chirp and for right side filtering with modulators with positive chirp.

Abstract: The invention relates to a regenerator using optical phase modulation in an optical fiber transmission system using soliton signals. According to the invention, the soliton signal is modulated by a clock in a modulator which is itself contained in an interferometer; the output signal from the interferometer has intensity that is representative of the phase difference between the clock and the soliton signal, and is therefore suitable for use in controlling the phase of the clock. In an embodiment, the interferometer is a Sagnac interferometer constituted by a non-linear optical loop mirror, and the modulation is distributed phase modulation in the transmission fiber. This enables the clock to be synchronized in simple manner.

Abstract: The invention relates to a wavelength division multiplex transmission system; for one channel, the spectral interval between adjacent channels on one side is different from the spectral interval between adjacent channels on the other side. A demultiplexing filter is used which attenuates more strongly the spectrum of the channel on the side on which the spectral interval between adjacent channels is smaller. The invention improves spectral efficiency and retains frequencies chosen from a grid of regularly spaced frequencies.

Abstract: The invention provides a regenerator for very high rate solitons, the regenerator comprising a non-linear loop mirror or NOLM receiving the soliton signal and modulating it with a control signal. The regenerator also comprises a device for generating the control signal by beats between two light sources, with the frequency of at least one of the two sources being variable and servo-controlled as a function of the modulated soliton signal, e.g. as a function of its power, or servo-controlled by means of an optical phase-lock loop. This provides a soliton regenerator in which the electronic components operate at low frequency only, while being capable of regenerating a soliton signal at a very high rate.

Abstract: In a wavelength-division multiplex fiber optic soliton signal transmission system the wavelengths of the multiplex are chosen to assure a relative slippage between the channels at a given interval substantially equal to a multiple of the bit time. At one point of the transmission system at least, the soliton pulses of the various channels have a temporal offset relative to a given reference such that, on distributed optical modulation by a clock that is input at this point, for each channel, the extremum of the non-linear phase profile induced by the clock, integrated over the modulation length, coincides with the center of the bit time. In a system of this kind distributed optical modulation can be applied to all the channels of the multiplex by a single sinusoidal signal. The modulation can be effected in a non-linear optical loop mirror or in the transmission fiber itself.

Abstract: In an optical modulation method a wave to be modulated and an optical control wave are injected simultaneously and colinearly into the same waveguide formed in a semiconductor diode that is reverse-biased so that the waveguide and the diode constitute the semiconductor part of an electro-absorption modulator. The wavelength of the control wave is shorter than that of the wave to be modulated. The impedance at the terminals of the diode is sufficiently high to enable amplitude modulation of the control wave to be transferred to the wave to be modulated. Applications include fiber optic telecommunication systems, in particular for resynchronizing solitons.

Abstract: The invention relates to a Kerr type optical modulator and to an all-optical clock recovery circuit operating by active mode locking of a fiber loop laser including such a modulator. Operation is independent of the polarization of the signals presented to the signal input, at wavelength .lambda..sub.s. The wavelength of the clock signal delivered by the clock recovery circuit is .lambda..sub.c. The modulator comprises an even number of segments, and in a preferred embodiment four segments of polarizationmaintaining fiber, with the segments being of equivalent optical lengths, and interconnected by three splices at three locations. At the first and third splices, the neutral propagation axes of the polarization-maintaining fiber are turned through 90.degree..

Abstract: The invention relates to an adjustable optical amplitude and phase modulator using a non-linear optical loop mirror having two control inlets and a signal inlet. In a preferred embodiment, a single clock signal is split into two and applied to the two control inlets. The invention also relates to a soliton regenerator including said optical modulator. In an important variant, said modulator receives a soliton bit train on its signal inlet at a bit rate f.sub.s, and on its control inlets it receives a clock signal at half that frequency f.sub.c =f.sub.s /2. In an advantageous embodiment, said clock signal is applied with a phase shift of .pi. between the two control inlets, so as to minimize the effects of collisions between solitons. The invention is applicable to long distance telecommunications by optical fiber.

Abstract: The invention relates to a non-linear optical mirror comprising an optical fiber loop that operates independently of the polarizations of the signals of respective wavelengths .lambda..sub.s and .lambda..sub.c present on its signal and control inputs. The loop of the NOLM is made up of four polarization-maintaining fiber segments having equivalent optical lengths. These four segments are optically optically interconnected by three splices at three locations. At the first and third splices, the neutral propagation axes of the polarization-maintaining fibers are turned through 90.degree.. According to the invention, a mode converter is inserted in the loop at the second splice, the converter comprising an optical demultiplexer and an optical multiplexer together with two polarization-maintaining optical paths inter-connecting them. The demultiplexer separates the two optical signals present at its input and applies them respectively to said two paths. On the path conveying the control signal, .lambda..sub.

Abstract: The apparatus of the invention regenerates solitons in-line by synchronously modulating the solitons using a non-linear optical loop mirror as an optical modulator, the NOLM modulator being controlled by a clock signal recovered from the soliton signal by clock recovery means which may be all-optical means or electro-optical means. The NOLM includes an input coupler which may be a 50/50 coupler or an asymmetrical coupler. Said input coupler may be a 2x2 coupler or a 3x3 coupler. In a particular embodiment, the regenerating system further includes a plurality of optical amplifiers and a plurality of "guiding" filters. Application to long-distance soliton optical telecommunications.