Abstract: Verifying a configuration of reconfigurable internal optical paths (970) in a wavelength selective optical switching WSS node (62) involves identifying which of several WSS subsystems (920, 950, 960) is coupled upstream of a first internal optical path based on detecting optical power distinctive of the upstream subsystem and carried to the downstream WSS subsystem. The detecting can be of a power of wavelengths used for traffic (110), or a power of optical noise when there is no traffic (120). A record is made of the identified configuration. The automated verification can be carried out without the conventional dedicated optical wavelengths or dedicated optical hardware for inserting such additional wavelengths dedicated to discovery, and without disrupting the traffic if upgrading a node. It can be controlled locally or by an NMS such as an SDN controller.

Abstract: A network node (400) for use with a single-fiber bidirectional communication link comprises a filter (300). The filter (300) comprises at least four ports. A first port (301) is configured to communicate with the single-fiber in a west direction. A second port (303) is configured to communicate with the single-fiber in an east direction. A third port (305) is configured to add/drop in the west direction. A fourth port (307) is configured to add/drop in the east direction. The network node is configured to add a first wavelength (?A) to the west direction and the east direction, and configured to drop a second wavelength (?B) from the west direction and the east direction.

Abstract: According to the present invention, there is provided apparatus for providing protection of an optical link. The apparatus comprises a first port for coupling to the optical link and a second port for coupling to a further optical link. The apparatus further comprises a third port configured to receive an upstream optical signal to be transmitted over the optical link, and to output a downstream optical signal received over the optical link. The apparatus further comprises protection switching apparatus operable to selectively couple the third port to the first port or to the second port. The apparatus further comprises modifying apparatus configured to modify the upstream optical signal, received at the third port, before it is output from the first port, such that the switching upstream optical signal has a distinctive physical characteristic.

Abstract: A method of managing a node in a cluster of nodes in an SDN network. The method comprising receiving from the node a request to join the cluster and a list of references authenticating the node. The references are verified and if the referenced passed the verification the node is allowed to join the cluster. Then a trust level of the node is calculated based on the number of verified references, wherein a role of the node in the cluster depends on the trust level of said node.

Abstract: According to embodiments of the present disclosure, apparatus is provided for protecting an optical link arranged to carry upstream optical signals and downstream optical signals. The apparatus comprises a first detector arranged to selectively detect a downstream optical signal received at a second port having a first wavelength and a second detector arranged to selectively detect a downstream optical signal received at the second port having a second wavelength different from the first wavelength. The apparatus further comprises control circuitry arranged to cause a protection switch to selectively couple a third port to the second port instead of to the first port based on the detecting by the first detector and the second detector. Also provided is a second apparatus for protecting the optical link.

Abstract: A method of automatically tuning subcarriers of a superchannel transmission. The method comprises determining (71) a received parameter of transmission quality of one or more of the plurality of subcarriers. The method further comprises tuning (72) a frequency of the one or more subcarrier based on the determined parameter of the transmission quality.

Abstract: According to the present invention, there is provided apparatus for providing protection of an optical link. The apparatus comprises a first port for coupling to the optical link and a second port for coupling to a further optical link. The apparatus further comprises a third port configured to receive an upstream optical signal to be transmitted over the optical link, and to output a downstream optical signal received over the optical link. The apparatus further comprises protection switching apparatus operable to selectively couple the third port to the first port or to the second port. The apparatus further comprises modifying apparatus configured to modify the upstream optical signal, received at the third port, before it is output from the first port, such that the switching upstream optical signal has a distinctive physical characteristic.

Abstract: A method of transmitting communications traffic in an optical communication network comprising a plurality of nodes, the method comprising, at a source node: receiving communications traffic to be transmitted across the optical communication network to a target node; obtaining a path sequence defining an order in which a plurality of optical paths from the source node to the target node across the optical communication network are to be used, at least part of each optical path being spatially separate from each other optical path; and transmitting the communications traffic as a series of traffic portions, each traffic portion being transmitted for a respective preselected transmission period on a respective optical path according to the path sequence.

Abstract: Verifying a configuration of reconfigurable internal optical paths (970) in a wavelength selective optical switching WSS node (62) involves identifying which of several WSS subsystems (920, 950, 960) is coupled upstream of a first internal optical path based on detecting optical power distinctive of the upstream subsystem and carried to the downstream WSS subsystem. The detecting can be of a power of wavelengths used for traffic (110), or a power of optical noise when there is no traffic (120). A record is made of the identified configuration. The automated verification can be carried out without the conventional dedicated optical wavelengths or dedicated optical hardware for inserting such additional wavelengths dedicated to discovery, and without disrupting the traffic if upgrading a node. It can be controlled locally or by an NMS such as an SDN controller.

Abstract: A method (10) of non-linear propagation impairment equalization, the method comprising the steps of: a. receiving (12) communications traffic carried by an optical communications signal transmitted over an optical communications link; b. generating (14) a time dependent filter representation of a nonlinear time-variant impulse response of the inverse of the optical communications link; and c. applying (16) the time dependent filter representation to the received communications traffic to form non-linear propagation impairment equalized communications traffic. An optical communications link nonlinear propagation impairment equalizer and optical communications signal receiver apparatus are also provided.

Abstract: An optical multi carrier signal has a modulation format and has many individual carrier signals. Parameters of the signal are controlled by receiving an indication of individual carrier transmission performance of the individual carrier signals, and selecting parameter values for the individual carrier signals, the parameter values comprising both a carrier FEC overhead and a carrier bandwidth for the modulation format. Selection is made according to the indicated individual carrier transmission performance and according to an overall spectral efficiency of the multi carrier signal. The selected parameter values are output for control of the optical multi carrier signal. By selecting values for both parameters rather than either one, better optimization can be obtained since they are interdependent. The control can have better granularity than changing modulation format, and can make better use of bandwidth or improve the overall capacity.

Abstract: Apparatus (10) for an optical communications network has optical paths for optical traffic, and optical ports (20,40), one of which is an unused input port (20). A security monitoring system (30) has a blocking part (50) comprising an interface (51) coupled removably to the unused input port (20) to occupy it to prevent unauthorized access. A light source is optically coupled to the interface (51) such that, when the interface is coupled to the unused input port, light can be transmitted through the interface (51) into the unused input port (20). An optical detector (60) can detect light reflected back from the interface (51), and there is alarm circuitry (70) configured to output an alarm signal based on the detecting of the reflected light. This monitoring can help make the node more secure from interference such as the introduction of a noise signal. The system can be passive or active, and does not require a change in the installed node configuration and so can be added easily to existing infrastructure.

Abstract: A method (10) of non-linear propagation impairment equalisation, the method comprising the steps of: a. receiving (12) communications traffic carried by an optical communications signal transmitted over an optical communications link; b. generating (14) a time dependent filter representation of a nonlinear time-variant impulse response of the inverse of the optical communications link; and c. applying (16) the time dependent filter representation to the received communications traffic to form non-linear propagation impairment equalised communications traffic. An optical communications link nonlinear propagation impairment equaliser and optical communications signal receiver apparatus are also provided.

Abstract: Apparatus for an optical communications network has optical paths for optical traffic, and optical ports, one of which is an unused output port. A security monitoring system has a blocking part coupled removably to the unused output port to occupy it to prevent unauthorized access. An optical detector can detect optical signals passing through the unused output port to the blocking part, and there is alarm circuitry configured to output an alarm signal based on the detecting of the optical signals. This monitoring can help make the node more secure from interference or from eavesdropping. By blocking the port, the monitoring can be independent of the type of signals on the optical paths. The system can be passive or active, and does not require a change in the installed node configuration and so can be added easily to existing infrastructure.

Abstract: An optical transmitter has a modulator for modulating data onto an optical signal for transmission to the receiver, the modulated signal having components at one or more constellations of points of different amplitudes and phases. The modulator is tunable such that distortions of the points of the one or more constellation can be tuned, and a tuning controller is provided for receiving a feedback signal from the receiver indicating a distortion measured at the receiver, and for tuning automatically the modulator to adjust the modulation based on the received feedback signal to pre-compensate for the measured distortion. Such pre-compensation can reduce the amount of distortion in the transmission system and thus enable more transmission capacity, without the need for a complex transmitter.

Abstract: A path computation client (PCC) can request a path computation element (PCE) to compute a path across a wavelength switched optical network. PCC sends a request which identifies end nodes. The end nodes can support a plurality of possible values of a transmission parameter, such as modulation format or Forward Error Correction (FEC) type. The PCE computes a path between the end nodes and sends a reply to the PCC. The reply identifies the path between the end nodes and identifies a selected value of the transmission parameter for the computed path. The reply can comprise a spectrum assignment for the path. The reply can be a PCE Communication Protocol (PCEP) Reply message.

Abstract: A method includes: selecting an optical pump signal power of a Raman amplifier such that a saturated gain of the Raman amplifier is at a maximum operating level without exceeding a gain threshold above which an optical signal to noise ratio penalty is no longer negligible in the Raman amplifier; selecting an optical signal power for at least one optical communication signal to be transmitted across the optical link to maximise a Q-factor of the optical signal when the Raman amplifier is configured for said maximum operating level of the saturated gain; generating a pump signal power control signal to cause an optical pump signal source of the Raman amplifier to generate an optical pump signal having the selected optical pump signal power; and generating a signal power control signal configured to cause the optical communication signal to be delivered into the optical link at the selected optical signal power.

Abstract: A method of transmitting communications traffic in an optical communication network comprising a plurality of nodes, the method comprising, at a source node: receiving communications traffic to be transmitted across the optical communication network to a target node; obtaining a path sequence defining an order in which a plurality of optical paths from the source node to the target node across the optical communication network are to be used, at least part of each optical path being spatially separate from each other optical path; and transmitting the communications traffic as a series of traffic portions, each traffic portion being transmitted for a respective preselected transmission period on a respective optical path according to the path sequence.

Abstract: A method of detecting a signal in an optical receiver is described. The method includes converting a received optical signal to a digital electrical signal comprising a plurality of samples, applying a predetermined phase rotation to said samples to obtain amplitude and phase components of phase range adjusted sample values, and performing a first detection process based on the amplitude and phase components of the phase range adjusted sample values.

Abstract: Chromatic dispersion (CD) processing apparatus comprises an equalizer loop comprising: a frequency domain equalizer (FDE) arranged to receive samples of an electrical representation of an optical communications signal having CD and to apply CD compensation to the samples, to form dispersion corrected samples having a residual CD value; a time domain equalizer arranged to receive the corrected samples and to generate a representation of a channel linear transfer function of the signal from the corrected samples, to generate and transmit a monitoring signal comprising said representation; optical performance monitoring apparatus arranged to receive the monitoring signal and to estimate the residual CD value; and a processor arranged to receive the estimated residual value and to compare it to a threshold value and to generate and transmit to the FDE an estimation signal comprising the estimated value unless it is less than the threshold.