Abstract: Various high loss loop back (HLLB) repeater architectures are disclosed that enable selectively monitoring (e.g., measuring, analyzing, etc) of Rayleigh signals from both inbound and outbound directions of an optical communication system. In one such embodiment, first and second optical test signal frequencies (or ranges) are used, in conjunction with selective filtering, for monitoring the outbound and inbound paths, respectively. The repeater architectures allow optical time domain reflectometry (OTDR) monitoring techniques to be employed, for example, in particularly long repeater spans, such as those in excess of 90 km in length.

Abstract: A system and method for suppressing beat noise in line monitoring equipment. A wavelength dither generator wavelength modulates a carrier wavelength of a test signal laser transmitter. A test code is modulated on the dithered carrier wavelength to provide a test signal output of the line monitoring equipment.

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 multiple conductor optical cable may be coupled to an undersea device, such as a cable joint, branching unit, or repeater, with one or more isolated bypass conductive paths being provided across the undersea device. At least one conductor may be terminated within a housing of the undersea device and at least one conductor may be coupled to a conductive bridge member that provides the isolated bypass conductive path across the device. Multiple conductor optical cables may be coupled to undersea devices in optical networks using independent power paths, for example, to deliver power to different powered components at different voltage potentials.

Abstract: An optical amplifier including gain equalization and system incorporating the same. The amplifier includes a Raman portion and an EDFA portion with a gain flattening filter coupled between the Raman portion and the EDFA.

Abstract: An optical add-drop network and wavelength allocation for the same wherein the system bandwidth is separated into a dedicated channel band and re-used channel bands, separated by guard bands, to allocate terminal connections to achieve a minimum number of re-used channel bands for the desired terminal connectivities.

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 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: 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 system and method for time domain reflectometry (OTDR) using multi-resolution code sequences. One or more subsets of a set of predefined complementary code sequences may be transmitted as an OTDR signal to provide multi-resolution capability.

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 and method using differential loop gain for fault analysis in line monitoring equipment. Differential loop gain data is calculated from loop gain data, and fault analysis is conducted using differential loop gain data, e.g. by comparing the differential loop gain data to predefined fault signatures.

Abstract: A distortion compensation system and method may be used to compensate for data pattern dependent signal distortion in a signal received in a coherent optical signal receiver. In general, the distortion compensation system and method compares a received signal field with stored distorted signal waveforms associated with known data patterns and selects a compensation value associated with the distorted signal waveform that corresponds most closely with the received signal field. The distortion compensation system and method compensates the received signal using the selected compensation value and thus mitigates the effects of data pattern dependent signal distortion.

Abstract: A system and method implementing dual stage carrier frequency offset compensation (FOC) in a coherent receiver for an optical communication system. In the first stage, a feed forward FOC function compensates for relatively slowly drifting frequency offsets. In a second stage, a decision-feedback FOC function compensates for relatively quickly drifting frequency offsets. The feed forward frequency offset compensation may be implemented with a feed forward carrier phase estimation function and the decision-feedback frequency offset compensation may be implemented with a decision-feedback carrier phase estimation function.

Abstract: A detection system and method may be used to detect data transmitted in a signal with data pattern dependent signal distortion such as intersymbol interference. In general, a detection system and method compares samples of a received signal with stored samples of distorted signals associated with known data patterns and selects the known data patterns that correspond most closely with the samples of the received signal. The detection system and method may thus mitigate the effects of data pattern dependent signal distortion.

Abstract: A detection system and method may be used to detect data transmitted in a signal with data pattern dependent signal distortion. In general, a detection system and method compares samples of a received signal with stored samples of distorted signals associated with known data patterns and selects the known data patterns that correspond most closely with the samples of the received signal. The detection system and method may thus mitigate the effects of data pattern dependent signal distortion.

Abstract: A system and method implementing dual stage carrier phase estimation (CPE) in a coherent receiver for an optical fiber communication system. In the first stage, a feed-forward CPE is implemented to make an initial carrier phase estimation of a training sequence. The initial carrier phase estimation is coupled to the second stage which implements a decision-feedback CPE. After a training period, accurate bit decision for system traffic can be achieved using the decision-feedback CPE.

Abstract: A system and method using for wavelength monitoring and control in a WDM optical communication system. An aggregate channel monitor detects crosstalk between channels in the aggregate signal. Channel spacing may be modified by an element management system in response to the output of the aggregate channel monitor.

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: Dispersion may be managed in an optical network configured to transmit differential phase shift keying (DPSK) modulated signals by allowing accumulation of dispersion to thousands of ps/nm before compensating. A dispersion map providing a negative average dispersion and a minimum dispersion wavelength outside of the signal band may be employed.