Abstract: Methods and apparatus for determining transmission power of a plurality of optical channels for transmission of the channels along respective paths obtained through an optical transmission system. Information is obtained indicative of the path of each channel through the optical transmission system, and each channel allocated to a group of channels in dependence upon the obtained information. A quality metric is determined for each group of channel, and a total transmission power for each group determined in dependence upon the determined quality metric.

Abstract: The invention relates to improvements in or relating to optical networks. Methods and apparatus are disclosed for providing communications services to at least one user. Transmission of an optical signal in the downstream direction is described comprising at least one Wavelength Division Multiplexing channel such that at least one of the channels is an unmodulated channel. The unmodulated channel is arranged to transmit user data from the at least one user in the upstream direction.

Abstract: An optical PON network comprises a central office which generates N DPSK modulated optical signals, where N is an integer greater than 1, an optical coupling which connects the N signals to at least one optical fibre, a passive distribution mode located remotely from the central office which has at least one input port that is coupled to the fibre and a plurality of output node being arranged to transmit a first wavelength of the N signals to at least one of its output ports, and at least one optical network unit connected through a respective optical fibre to the first output port of the passive distribution node. The passive distribution node comprises an arrayed waveguide grating which provides a passive optical connection between its input port and the first output port and which for that connection functions as a bandpass filter having a profile and bandwidth selected such that the DPSK optical signal passed to the input node is converted to an intensity modulated signal at the output port.

Abstract: Optical signal processing apparatus for processing packetised optical signals comprising a probe signal generator which is arranged to issue a plurality probe pulses, and an optical AND logic gate assembly, the arrangement of the apparatus being such that, in use, the probe signals have an interval between pulses substantially equal to the interval between data elements of the packetised data to be extracted, and the packetised data and the probe pulses are then combined by the AND logic gate assembly.

Abstract: A signal processor for compensating for optical fibre chromatic dispersion comprising encoding means (5) for encoding a source signal (2) received from a data source (6), splitting means (8) to separate the encoded signal (7) from the encoding means (5) into an in-phase component (10) and an in-quadrature component (11), a first filter means (12) adapted to receive the in-phase component (10) and a second filter means (13) adapted to receive the in-quadrature component (11), the first filter means (12) and second filter means (13) being adapted to filter the in-phase and in-quadrature components respectively. The outputs (14, 15) from the filter means form the input to the optical modulator means (3).

Abstract: An optical transmitter apparatus for use in an optical communications network has a polarization dithering unit, an optical transmitter unit, and a transmission fiber. The polarization dithering unit is connected in series between an output of the optical transmitter unit and the transmission fiber.

Abstract: An iterative method for power pre-emphasis of N optical channels in a Wavelength Division Multiplex (WDM) signal in an optical communication systems in accordance with which representative Xi characteristics are defined for the channels with among the characteristics there being included at least one characteristic that is a function of the Bit Error Rate (BER).

Abstract: An optical modulation converter (10) for converting the modulation format of an optical input signal is characterized by a birefringent medium (14), polarization maintaining fibre, with a selected differential group delay between its two main axes of symmetry through which the optical input signal is passed to be separated into two optical components each travelling along one of the main axes of the medium at a different group velocity to thereby convert the modulation format of the input signal. By appropriate selection of the differential group delay imparted by the medium relative to the bit rate of the input signal and by appropriately presenting the input signal relative to the main axes of the medium conversion between different modulation formats can be achieved.

Abstract: In a communication system with an optical fibre transmission line (3), a compensation of chromatic dispersion due to the fibre (3) is performed through at least one compensation module (4; 4A . . . 4N) based on chirped optical fibre gratings having a group delay characteristic &tgr;(&ohgr;) which exhibits ripples around a nominally linear profile, as a function of the optical signal frequency. To minimise the effect of said ripples, the compensation is carried out in such a way that, for a given fibre length (3), the operating point is located in a limited slope region along the curve representative of system performance degradation owing to chromatic dispersion.

Abstract: The modification is accomplished on the basis of the solution known as spectral inversion (or optical phase conjugation). The device (1) comprises a medium, such as typically a dispersion shifted optical fiber (4), into which the signal to be modified is injected together with a pump signal at such a level as to induce modulation instability in the fiber (4). At the output of fiber (4) a spectrally inverted optical signal is available, which signal is translated in wavelength and is obtained with high conversion efficiency. Preferably, in order to avoid stimulated Brillouin scattering, the pump signal is subjected to spectrum broadening, for instance by means of a modulator (5).

Abstract: A train of rectangular pulses is sent into a fiber, which pulses have such a wavelength that fiber operates under anomalous dispersion conditions, such a peak power as to cause modulation instability in the fiber and such a ratio between duration and repetition period that the average power is lower than the threshold at which stimulated Brillouin effect takes place. The maximum value of instability gain is measured in the spectrum of the pulses exiting the fiber and the Kerr non linearity coefficient is obtained from the maximum measured value of modulation instability gain by minimizing the error, in the range of power values used for the measurement, with respect to a theoretical curve expressing such maximum gain as a function of the peak power. The device to realize the method is also provided.