Abstract: In general, a branching configuration used in a wavelength division multiplexed (WDM) optical communication system includes a branching unit (BU) and a separate predetermined wavelength filter (PWF) unit. The PWF unit may include wavelength selective elements (e.g., filters) for providing a desired wavelength allocation and may also include optical connections (e.g. optical couplers) for coupling the allocated wavelengths between trunk and branch paths in the WDM system. The PWF unit is physically separate from an associated BU but coupled adjacent the BU.

Abstract: A system for signaling between elements in an undersea optical communication system including a cable signal generator. The signal generator includes line current modulation circuitry configured to impart modulation in line current provided on a power conductor of the transmission cable. A method of signaling between elements in an undersea optical communication system includes modulating a line current through an element and detecting the modulated current.

Abstract: An optical add/drop multiplexer (OADM) and system incorporating the same for maintaining loading of WDM channels with loading signals or information signals when signals are added or dropped. The OADM may include reconfigurable band pass filters having a transmittance characteristic controllable using a command signal. Selective filtering of loading signals and/or information signals received from branch and trunk paths allows an output WDM signal including information signals on utilized channels and loading signals on all unutilized channels.

Abstract: Fault tolerance may be achieved in a branched optical communication system such that a fault in one optical path may not affect optical signals coupled from a healthy optical path. In general, a flexible branching unit is configured, when adding and dropping channels, to select channels from a healthy path and not from the faulty path (e.g., a trunk path or a branch path) to prevent non-uniform channel loading on the trunk path after the branching unit. In this manner, a fault detected on the trunk path may not affect signals from the branch path and a fault detected on the branch path may not affect signals from the trunk path, thereby providing fault tolerance. A flexible branching unit may also be capable of adjusting the number and selection of channels that are added and dropped at the branching unit.

Abstract: Fault tolerance may be achieved in a branched optical communication system such that a fault in one optical path may not affect optical signals coupled from a healthy optical path. In general, a flexible branching unit is configured, when adding and dropping channels, to select channels from a healthy path and not from the faulty path (e.g., a trunk path or a branch path) to prevent non-uniform channel loading on the trunk path after the branching unit. In this manner, a fault detected on the trunk path may not affect signals from the branch path and a fault detected on the branch path may not affect signals from the trunk path, thereby providing fault tolerance. A flexible branching unit may also be capable of adjusting the number and selection of channels that are added and dropped at the branching unit.

Abstract: A system and method for loading unutilized channels of a WDM system with noise to improve system performance. A transmitter amplifier may impart noise to unutilized channels by reducing amplifier input or providing feedback of the amplifier output. Noise signals may also be looped back to the transmitter from received signals.

Abstract: A monitoring system and method may be used to monitor an optical communication system. A monitoring system and method may be used to derive loop gain data sets from optical time domain reflectometry (OTDR) or coherent optical time domain reflectometry (COTDR) data. A monitoring system and method may also use differential monitoring techniques to obtain data representing gain tilt in the transmission system and to locate an anomalous loss or gain in the transmission system.

Abstract: In general, a branching configuration used in a wavelength division multiplexed (WDM) optical communication system includes a branching unit (BU) and a separate predetermined wavelength filter (PWF) unit. The PWF unit may include wavelength selective elements (e.g., filters) for providing a desired wavelength allocation and may also include optical connections (e.g. optical couplers) for coupling the allocated wavelengths between trunk and branch paths in the WDM system. The PWF unit is physically separate from an associated BU but coupled adjacent the BU.

Abstract: A method of managing gain tilt in an optical transmission segment including providing an optical transmission segment having a plurality of fiber optic cable spans and a plurality of repeaters coupled to the fiber optic cable spans. Gain tilt in the optical transmission segment is monitored. If negative gain tilt is accumulated at a repeater location in the transmission segment, the repeater at the repeater location is replaced with a higher gain repeater having a higher nominal gain value than the nominal gain value of the repeater being replaced.

Abstract: An optical add/drop multiplexer (OADM) and system incorporating the same for maintaining loading of WDM channels with loading signals or information signals when signals are added or dropped. The OADM may include reconfigurable band pass filters having a transmittance characteristic controllable using a command signal. Selective filtering of loading signals and/or information signals received from branch and trunk paths allows an output WDM signal including information signals on utilized channels and loading signals on all unutilized channels.

Abstract: An apparatus and method directed to testing and optimizing performance of an optical transmission system is disclosed, including at least one broadband dispersion compensation unit (DCU) or at least one depolarization device. The depolarization device may be used alone or in combination with the at least one broadband DCU. A method for optimizing performance of data channels in initial loading (IL) and full loading (FL) configurations of the optical transmission system is also disclosed.

Abstract: A system and method for loading unutilized channels of a WDM system with noise to improve system performance. A transmitter amplifier may impart noise to unutilized channels by reducing amplifier input or providing feedback of the amplifier output. Noise signals may also be looped back to the transmitter from received signals.

Abstract: An apparatus and method directed to testing and optimizing performance of an optical transmission system is disclosed, including at least one broadband dispersion compensation unit (DCU) or at least one depolarization device. The depolarization device may be used alone or in combination with the at least one broadband DCU. A method for optimizing performance of data channels in initial loading (IL) and full loading (FL) configurations of the optical transmission system is also disclosed.

Abstract: A system and method for loading unutilized channels of a WDM system with noise to improve system performance. A transmitter amplifier may impart noise to unutilized channels by reducing amplifier input or providing feedback of the amplifier output. Noise signals may also be looped back to the transmitter from received signals.

Abstract: An apparatus and method directed to testing and optimizing performance of an optical transmission system is disclosed, including at least one broadband dispersion compensation unit (DCU) or at least one depolarization device. The depolarization device may be used alone or in combination with the at least one broadband DCU. A method for optimizing performance of data channels in initial loading (IL) and full loading (FL) configurations of the optical transmission system is also disclosed.

Abstract: A system for signaling between elements in an undersea optical communication system including a cable signal generator. The signal generator includes line current modulation circuitry configured to impart modulation in line current provided on a power conductor of the transmission cable. A method of signaling between elements in an undersea optical communication system includes modulating a line current through an element and detecting the modulated current.

Abstract: A monitoring system and method may be used to monitor an optical communication system. A monitoring system and method may be used to derive loop gain data sets from optical time domain reflectometry (OTDR) or coherent optical time domain reflectometry (COTDR) data. A monitoring system and method may also use differential monitoring techniques to obtain data representing gain tilt in the transmission system and to locate an anomalous loss or gain in the transmission system.

Abstract: A method of managing gain tilt in an optical transmission segment including providing an optical transmission segment having a plurality of fiber optic cable spans and a plurality of repeaters coupled to the fiber optic cable spans. Gain tilt in the optical transmission segment is monitored. If negative gain tilt is accumulated at a repeater location in the transmission segment, the repeater at the repeater location is replaced with a higher gain repeater having a higher nominal gain value than the nominal gain value of the repeater being replaced.

Abstract: An optical transmission system may include a combination of higher gain repeaters and lower gain repeaters, arranged to manage gain tilt. The higher gain repeaters and lower gain repeaters may be arranged to allow net gain to vary (e.g., above and below zero) within a predetermined acceptable net gain excursion. In one embodiment, the higher gain repeaters have a nominal gain value higher than a nominal span loss value and the lower gain repeaters have a nominal gain value lower than the nominal span loss value.

Abstract: Dispersion may be managed in a branched optical network by using transmission segments having a single period segment dispersion map. One or more of such segments may be coupled to network nodes such as terminals or branching units such that dispersion may be managed even when the network is reconfigured. In one embodiment, a single period segment dispersion map provides dispersion compensation at the ends of the segment. In another embodiment, a single period segment dispersion-map provides dispersion compensation at the middle of the segment.