Abstract: The present application describes methods and systems for use in a communications network. More specifically, a method of deploying an optical demodulator arrangement having at least one interferometer in a network that transmits an optical signal is provided. The optical signal may include one or more on-off-keyed signals and one or more DMPSK signals. In some embodiments, the DMPSK signal is a DQPSK signal. The network may include one or more of fiber spans carrying the signals. The interferometer may have a first optical path and a second optical path and a time delay is formed between the first and second optical paths. The method may involve determining a cross-talk penalty that results from cross-phase modulation between the channels, and determining a time delay value for the interferometer. The time delay value may be determined based at least in part on determined the cross-talk penalty.

Abstract: A signal recovery system for a phase modulated signal having a signal spectrum, wherein the phase modulated signal is passed along a communications system (1) having at least one filter (3) so as to define the frequency channel of the communication system. Losses result from the passage of the signal through the at least one filter (3) defining the transmission channel. The signal recovery system recovers at least some of the losses by introducing a relative frequency offset between the signal spectrum and the transmission spectrum of the at least one filter (3) in the communications system.

Abstract: The present application describes methods and systems for use in a communications network. More specifically, a method of deploying an optical demodulator arrangement having at least one interferometer in a network that transmits an optical signal is provided. The optical signal may include one or more on-off-keyed signals and one or more DMPSK signals. In some embodiments, the DMPSK signal is a DQPSK signal. The network may include one or more of fiber spans carrying the signals. The interferometer may have a first optical path and a second optical path and a time delay is formed between the first and second optical paths. The method may involve determining a cross-talk penalty that results from cross-phase modulation between the channels, and determining a time delay value for the interferometer. The time delay value may be determined based at least in part on determined the cross-talk penalty.

Abstract: A method of reducing Raman tilt in a transmission apparatus capable of transmitting a plurality of signals, occupying contiguous channels in a transmission band, through a length of optical transmission cable which exhibits the Raman effect of transferring energy from the shorter wavelength signals at one end of the transmission band towards the longer wavelength signals at the other end of the transmission band, including the transmission of half the maximum number of signals at twice the normal channel frequency spacing at a higher-than-normal level and the transmission signals in selected ones, fewer than all, of the available channels at the normal channel spacing at a normal power level. As new channels are added at the lower frequency channel spacing, the powers of both neighboring channels are reduced to the normal power level.

Abstract: A dispersion management system for soliton or soliton-like transmission systems comprises a length of optical fibre (L) in which a plurality of sections (l) made up of components (N, A) of opposite sign dispersions are concatenated together. The duration of the dispersion compensation phase is short in comparison with the propagation interval in the remainder of the system and that the path average dispersion is anomalous.

Abstract: An apparatus and method of transmitting a plurality of polarized signals having different wavelengths through a length of signal transmission cable which changes the polarization of the signals in correspondence with their amplitudes and wavelengths. A dynamic filter capable of differential adjustment of the amplitudes of the signals and a polarizing element are provided in series with the length of signal transmission cable and the amplitudes of the different wavelength signals are so adjusted that the polarization states of the signals move towards alignment with the low-loss axis of the polarizing element. An advantage provided by the apparatus and method is that the high-amplitude signals are aligned with the low-loss axis of the polarizing element while low-amplitude noise is aligned with the high-loss axis of the polarizing element, resulting in an improvement in signal-to-noise ratio.

Abstract: A dispersion management system for soliton or soliton-like transmission systems comprises a length of optical fiber (L) in which a plurality of sections (I) made up of components (N,A) of opposite sign dispersions are concatenated together. The duration of the dispersion compensation phase is short in comparison with the propagation interval in the remainder of the system and that the path average dispersion is anomalous.

Abstract: A soliton or soliton-like pulse-based optical communication system comprises a length of optical fibre divided into a plurality of sections arranged so that the average dispersion of the length of fibre is significantly different from the dispersion of each section.

Abstract: A soliton or soliton-like pulse-based optical communication system comprises a length of optical fibre divided into a plurality of sections arranged so that the average dispersion of the length of fibre is significantly different from the dispersion of each section.

Abstract: A return-to-zero pulse optical communication system includes fast saturable absorber means (F1,DSF) to provide substantially zero average dispersion in a single amplifier span (SIF,DSF) to reduce the effect of timing jitter an provide considerably enhanced propagation distances.

Abstract: A dispersion management system for soliton or soliton-like transmission systems comprises a length of optical fiber (L) in which a plurality of sections (l) made up of components (N,A) of opposite sign dispersions are concatenated together. The duration of the dispersion compensation phase is short in comparison with the propagation interval in the remainder of the system and that the path average dispersion is anomalous.

Abstract: A soliton or soliton-like pulse-based optical communication system comprises a length of optical fibre divided into a plurality of sections arranged so that the average dispersion of the length of fibre is significantly different from the dispersion of each section.

Abstract: An optical communications system comprises a laser (10) controlled to output a stream of soliton pulses (12) coupled to a beamsplitter arrangement (14, 20, 22) which converts the pulse stream (12) to a stream of pulses (24) having twice the pulse rate. This stream of pulses (24) is modulated to form a binary coded signal by modulator (24) as a series of binary digits each having one of two values in which a series of n optical soliton pulses, where n is an integer>1 is coupled into an optical fibre (4) at each occurrence of one of the two values. The optical fibre (4) and repeaters (6) provide a transmission link to a receiver (8). The present invention allows one to increase the average power within a bit without having to operate with shorter pulses that would otherwise be necessary with one soliton pulse per bit of prior art systems in order to avoid the limits inherent in single soliton pulse per bit prior art systems.

Abstract: A return-to-zero pulse optical communication system includes fast saturable absorber means (F1,DSF) to provide substantially zero average dispersion in a single amplifier span (SIF,DSF) to reduce the effect of timing jitter an provide considerably enhanced propagation distances.