Abstract: A method and apparatus is provided that yields improved performance of both single channel and WDM long-distance optical transmission systems by synchronously modulating of the transmitted signal's amplitude. An amplitude modulator receives an optical signal onto which data has been modulated at a predetermined frequency. The modulator re-modulates the amplitude of the optical signal in a continues fashion with a waveform that is periodic, whose fundamental frequency is equal to the same predetermined frequency at which the data is modulated onto the optical signal. The resulting signal (which is neither a pure NRZ or RZ signal) is more tolerant to the distortions usually found in lightwave transmission systems, thus giving superior transmission performance.

Abstract: A method and apparatus is provided for managing chromatic dispersion in an NRZ-based WDM long-haul optical transmission system so that nonlinearities are reduced, especially those at the edge channels of the band. The method includes using between 500 ps/nm and 2000 ps/nm of residual dispersion and a 40%/60% pre/post DCU split ratio when the channel wavelengths are shorter than the zero dispersion wavelength. Using these dispersion compensation rules, the nonlinear propagation effects in NRZ-based WDM systems is reduced, thus allowing for higher optical power per channel and/or longer transmission distances.

Abstract: A WDM optical transmission system and method uses slope compensation at the transmit terminal and/or the receive terminal. The system and method may be used with modulation formats with a short pulse width and a broad optical spectrum.

Abstract: An optical cable shield layer connection may include a wire electrically connected to a shield layer of an optical cable. The optical cable shield layer connection may also be sealed, for example, to prevent leak paths. The optical cable shield layer connection may be made when coupling the optical cable to a device or another cable, for example, using a universal joint such as the Millennia® Joint available from Tyco Telecommunications (U.S.) Inc. The wire may provide a ground path from the shield layer or a continuity path from the shield layer to another optical cable.

Abstract: The soft decision thresholds in a soft decision forward error correction (FEC) system may be adjusted based on mutual information of a detected signal. In one embodiment, a recursive algorithm may be used to optimize threshold values by maximizing the mutual information. In another embodiment, an adaptive scheme may be used to optimize threshold values based on a pre-knowledge of the noise in the channel. In a further embodiment, an adaptive scheme may be used to optimize threshold values by without pre-knowledge of the noise in the channel.

Abstract: A system and method for soft decision forward error correction (FEC) decoding may be used to determine a possible error in a differential detection signal, for example, in a DPSK system. The system and method uses the constructive and destructive signals from a demodulator to provide an error locating signal. Using the error locating signal, the system and method converts the differential detection signal into a soft decision signal including multi-level soft values.

Abstract: An optical receiver including a plurality of time delay elements and threshold decision elements configured to receive a signal representative of an optical signal. Each of the time delay elements is configured to impart an associated time delay to the signal. Each of the threshold decision elements is configured to compare the signal to a plurality of threshold levels. Each decision element outputs a signal indicative of a probability that a particular pulse of the received signal is a binary one at its associated sampling time. An optical communication system and a method of detecting a received data signal in an optical communication system are also provided.

Abstract: An optical communication system configured to operate with optical signals at lower signal to noise ratios than previously contemplated. The communication system includes a receiver having an optical pre-processor coupled between a demultiplexer and a detector. The optical pre-processor includes either an optical polarization section having a polarization rotator and an optical polarizer, a phase modulation section that includes a phase modulator and a dispersion element and a clock recovery circuit, or an amplitude modulation section that includes an amplitude modulator clock recovery circuit and a spectral shaping filter.

Abstract: A receiver for a differentially phase shift keying formatted optical signal, such as an RZ-DPSK formatted optical signal. Dither control loops are provided for controlling path length in a demodulator and/or for controlling the center wavelength of an optical band pass filter. A feedback loop is provided for controlling the gain of a pre-amplifier, and a method of protecting against optical transients by disabling a pre-amplifier is also provided. A preset delay may be provided to compensate for the differential delay in paths associated with the demodulator arms. When the signal is an RZ-DPSK modulated signal, a clock for retiming data from the optical signal may be derived from a signal on the data path.

Abstract: An optical cable shield layer connection may include a wire electrically connected to a shield layer of an optical cable. The optical cable shield layer connection may also be sealed, for example, to prevent leak paths. The optical cable shield layer connection may be made when coupling the optical cable to a device or another cable, for example, using a universal joint such as the Millennia® Joint available from Tyco Telecommunications (US) Inc. The wire may provide a ground path from the shield layer or a continuity path from the shield layer to another optical cable.

Abstract: A WDM optical transmission system and method uses slope compensation at the transmit terminal and/or the receive terminal. The system and method may be used with modulation formats with a short pulse width and a broad optical spectrum.

Abstract: A method and apparatus is provided that yields improved performance of both single channel and WDM long-distance optical transmission systems by synchronously modulating of the transmitted signal's amplitude. An amplitude modulator receives an optical signal onto which data has been modulated at a predetermined frequency. The modulator re-modulates the amplitude of the optical signal in a continuous fashion with a waveform that is periodic, whose fundamental frequency is equal to the same predetermined frequency at which the data is modulated onto the optical signal. The resulting signal (which is neither a pure NRZ or RZ signal) is more tolerant to the distortions usually found in lightwave transmission systems, thus giving superior transmission performance.

Abstract: An undersea equipment housing includes an inner housing, molded terminations secured at each end of the inner housing, and an outer strength housing. In one embodiment, the housing is used to house optical and electrical equipment, for example, in a repeater. The undersea equipment housing may also include a molded portion around an inside of the inner housing. The molded portion and the molded terminations provide voltage isolation.

Abstract: A system, amplifier and method are provided for amplifying an optical signal in an optical communications system where spans between amplifiers may vary. The system includes a Raman amplifier variable gain portion and an EDFA gain portion. The amount of Raman amplifier gain is chosen to trade off accumulation of noise with accumulation of multi-path interference. This variable Raman gain is used to equalize the loss of each span so that the amount of optical power supplied at the input of the EDFA gain portion is substantially constant throughout the system.

Abstract: An apparatus, system and method wherein a multi-level data modulation format, such as DQPSK, is combined with symbol rate synchronous amplitude, phase, and/or polarization modulation.

Abstract: A system and method for diagnosing faults in a communication network using a distributed alarm correlation system. The alarm correlation system may include node-level alarm correlation tools (ACTs) located at nodes in the network to provide node-level alarm correlation producing node-level correlation results. The node-level ACTs may share diagnostic knowledge with other node-level alarm correlation tools at other nodes. Each of the node-level ACTs may also share the diagnostic knowledge and the node-level correlation results with a higher-level ACT. The higher-level ACT may provide higher-level alarm correlation to produce higher-level correlation results.

Abstract: A system and method for optimizing dispersion in an optical transmission line is provided. The system and method comprise measuring the amplitude of a d.c. voltage component of a synchronously demodulated data signal of at least one wavelength channel by an in-phase carrier at the baud frequency of the wavelength channel. In an alternative embodiment, the system and method comprise measuring the IF amplitude of the resulting a.c. signal of a data signal of the at least one wavelength channel comprising a received RZ signal mixed with a local oscillator, whose frequency differs from the wavelength channel baud by a relatively small amount, somewhere on the order of about 100 kHz.

Abstract: A WDM optical transmission system and method uses slope compensation at the transmit terminal and/or the receive terminal. The system and method may be used with modulation formats with a short pulse width and a broad optical spectrum.

Abstract: A power feed arrangement for aggregate segments of a communications system is disclosed. In embodiments of the invention, cables are used to communicatively connect a number of landmasses, where the cables also serve to carry electrical power to devices connected along lengths of the cables. A first cable is connected to first and second landmasses, while a second cable is connected to second and third landmasses. On the second landmass, the electrical power conductors of the first and second cables are electrically connected to one another, and pieces of power feed equipment located on said first and third landmasses are used to supply electrical power to devices located along lengths of the first and second cables. Alternative embodiments are also disclosed.

Abstract: A protection switching architecture is used in a telecommunications system such as a wavelength division multiplexed (WDM) telecommunications system to replace a failed transmission line or a failed wavelength processing device. A spare wavelength processing device transmitter replaces a failed service wavelength processing device transmitter. A spare transmission line replaces a failed service transmission line. A spare wavelength processing device receiver monitors the optical signals, one wavelength at a time, on either the spare transmission line or the service transmission line and replaces one of the service wavelength processing device receivers. Wavelength selection equipment routes either the service transmission line or the service transmission line to the service wavelength processing device receivers and selects wavelengths to be monitored by the spare wavelength processing device receiver.