Abstract: A method of managing fault recovery in a trunk-branched OADM network may include determining that an optical power level over data channels of a first communications link between a first and a second terminal of the branched optical network exceeds an optical power limit. The method may further include increasing optical power sent over spare channels of the first communications link to a first level at which the optical power level over the data channels decreases to a second level below the optical power limit.

Abstract: A system and method for polarization de-multiplexing in a coherent optical receiver. De-multiplexing is achieved using a modified constant modulus algorithm (CMA) wherein filter coefficients are determined as a function of a coupling coefficient to avoid convergence of the CMA outputs.

Abstract: In general, optical communication systems and methods may generate higher-level nmQAM from nQAM signals using one or more delay line interferometers (DLIs) arranged in various configurations. The nQAM signals may be generated by a lower-level modulator, such as a BPSK modulator, QPSK modulator or lower-level QAM modulator, with binary driving signals. Different parameters of the DLIs, such as free spectral range (FSR), phase shift, and amplitude imbalance, may be selected to accomplish the desired higher-level nmQAM depending upon the nQAM signal.

Abstract: A repeater that enables both bi-directional optical time domain reflectometry (OTDR) and loop gain monitoring techniques that may be employed, for example, in particularly long repeater spans. In one embodiment, the repeater includes high loss loopback (HLLB) paths configured to couple test signals between incoming and outgoing fiber paths. The HLLB paths are coupled from the outputs to the inputs of amplifiers within the repeater and couple both OTDR and loopback signals from an outgoing fiber path to an incoming fiber path so that may be returned to line monitoring equipment that transmitted the test signals.

Abstract: A system and method with a modified bit-interleaved coded modulation with iterative decoding (BICM-ID). A first group of coded and interleaved bits are coded with a second FEC code and a second group of coded and interleaved bits are not coded with the second FEC code. The first and second groups are then mapped to a modulation format. The second FEC code may be a single parity check (SPC) and the scheme may be referred to as a BICM-ID scheme with a fractional secondary coding.

Abstract: A system and method for method of managing a network. Each of a plurality of servers includes an element management system (EMS) function for managing network elements within the network and a network management system (NMS) function for managing ones of the plurality of servers running the EMS function. An NMS function is activated on one of the servers when the plurality of servers shares a one network domain. When the network domain is divided into multiple domains, e.g. by a network failure, an NMS function is activated on at least one other one of the plurality of servers whereby each of the multiple network domains has at least one associated active NMS function.

Abstract: In general, a system and method provides secure communications between optical transceivers in an optical communication system. Two or more optical transceivers may be provisioned with one or more passcodes assigned to the transceivers, which may be used to indicate that received data traffic is intended for the transceivers. The transceivers may be configured to format data traffic with a secure version of the passcode in the overhead of the outbound signal and may be configured to determine if an inbound signal includes a secure version of the passcode provisioned in that transceiver. A transceiver may prevent data traffic from being read when the transceiver is not provisioned to receive data traffic with the embedded secure passcode and may insert an alternative maintenance signal (AMS) into an outbound signal in an opposite direction, at least temporarily, until the inbound signal includes the appropriate passcode.

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: In general, a wavelength division multiplexed (WDM) communication system may use wavelength selective switching to simultaneously pre-filter and combine groups of channel wavelengths with orthogonal polarizations to provide a pre-filtered, pair-wise orthogonal aggregate WDM optical signal. An orthogonally-combining wavelength selective switch (WSS) multiplexer may route channel wavelengths individually from different sets of channels to a common output. The orthogonally-combining WSS multiplexer may also provide substantially orthogonal polarizations for the wavelengths in the different sets of channels. The different sets of channels may include odd channels and even channels.

Abstract: An optical communication system supporting detection and communication networks. A communication network transmission path and the detection network transmission path are provided as separate paths established by separate fibers or fiber pairs of the same optical fiber cable. All of the elements coupled to the communication network transmission path and the detection network transmission path may be powered by the same power feed equipment through the same optical fiber cable power conductor.

Abstract: A system and method with a modified bit-interleaved coded modulation with iterative decoding (BICM-ID). A first group of coded and interleaved bits are coded with a second FEC code and a second group of coded and interleaved bits are not coded with the second FEC code. The first and second groups are then mapped to a modulation format. The second FEC code may be a single parity check (SPC) and the scheme may be referred to as a BICM-ID scheme with a fractional secondary coding.

Abstract: Methods and systems for processing an optical signal in a communication system are disclosed. The disclosed methods yield benefits for estimation and tracking of carrier phase of received signals at a digital coherent receiver. Specifically, phase ambiguity is removed by the insertion of pilot symbols into a transmitted data stream. Pilot symbols are detected from a received signal, and carrier phase is estimated for the detected pilot symbols. If carrier phase track of received data symbols was lost, a correction is applied to recover the track. Coherent symbol decoding may be used which has not been possible with prior art techniques due to the possibility of phase tracking loss.

Abstract: A soft decision threshold control system and method may be used with a forward error correction (FEC) scheme to adjust or tune one or more soft decision thresholds in response to one or more bit value averages for the threshold(s) and in response to a bit error rate (BER). The bit value average for a soft decision threshold generally refers to an average number of binary values (e.g., logic ones and/or zeros) occurring in a bit stream detected using the soft decision threshold. For different BER levels in a particular system, for example, one or more of the soft decision thresholds may have a predetermined bit value average, which has been determined to provide a certain level of performance (e.g., an optimum performance). Thus, one or more of the soft decision thresholds may be adjusted such that the bit value averages for the soft decision thresholds are adjusted as a function of the BER.

Abstract: An apparatus for underwater communications. The apparatus may include a high speed communications cable to provide an underwater hardwired communications link to a surface station and a mobile device operative to transport a first end of the high speed communications cable between a submarine and a coupling point to the surface communication station, wherein the high speed communications cable is operative to reversibly form a hardwired connection between the coupling point and the submarine.

Abstract: Methods and systems for processing an optical signal in a communication system are disclosed. The disclosed methods yield benefits for estimation and tracking of carrier phase of received signals at a digital coherent receiver. Specifically, phase ambiguity is removed by the insertion of pilot symbols into a transmitted data stream. Pilot symbols are detected from a received signal, and carrier phase is estimated for the detected pilot symbols. If carrier phase track of received data symbols was lost, a correction is applied to recover the track. Coherent symbol decoding may be used which has not been possible with prior art techniques due to the possibility of phase tracking loss.

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 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: Methods and systems for processing an optical signal in a communication system are disclosed. The disclosed methods yield benefits for estimation and tracking of carrier phase of received signals at a digital coherent receiver without the use of differential coding. Specifically, phase ambiguity is removed by calculating the slope of the CPE at a location where the CPE begins to lose track of the received carrier phase signal. As such, a CPE offset adjustment may be applied in accordance with the calculated slope to reduce the number of ones and zeros corrected by a FEC decoder. Thus, the FEC aided CPE scheme may be a feed forward scheme that requires no training.

Abstract: An inverse multiplexing communication path is established in at least one direction between nodes connected by a plurality of lower bandwidth bearing channels between the nodes, on which the content of a higher bandwidth signal is distributed and from which the original high bandwidth signal is recovered at the receiving node. During preliminary configuration, for example when selecting a subset of bearer channels from among a number of potential bearer channels, the bearer channels are chosen or are altered by signal processing to make the members of the subset perform similarly, thereby improving operations as compared to having the bearer channels bound to perform according to the performance of the least-performing member of the subset.

Abstract: A system and method for blind equalization of a QAM signal. Equalization is achieved using an algorithm characterized by cost function that is a function the Euclidian distance, e.g. the minimum Euclidian distance, between points of the constellation associated with the QAM signal, i.e. the distance between symbols.