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: 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 optimisation 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 unauthorised 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 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: Chromatic dispersion (CD) processing apparatus comprises an equalizer loop comprising: a frequency domain equaliser (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 equaliser 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.

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: 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 unauthorised 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: Path computation through nodes of a communications network to meet a desired security level against unauthorised physical access to the path, involves receiving a request (200) for selection of a new path, and using a record (210) of connectivity of the nodes and links with indications of a security level against unauthorised physical access to the path. This can enable the path routing to be made so as to assure a given level of security of the underlying hardware of nodes and links, in networks where not all parts can provide such security. Nodes can report their current security levels to update the record. A previously selected path can be validated by comparing indicated current security levels of the nodes of the path with the desired security level.

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 of monitoring a differential group delay (DGD) of an optical communications signal having a polarisation multiplexed modulation format is described. The method includes the operations of receiving a signal and performing analogue to digital conversion of the signal to generate a digitised signal corresponding to one polarisation of the signal and to generate another digitised signal corresponding to another polarisation of the signal, and applying a polarisation mode dispersion(PMD) compensation to each of the digitised signals. The method further includes the operations of obtaining an indication of the channel transfer function of the optical communications signal, determining a DGD in dependence on the indication of the channel transfer function, determining a delay between the PMD compensated digitised signals, subtracting the delay from the DGD to obtain a corrected DGD, and generating and transmitting a monitoring signal with an indication of the corrected DGD.

Abstract: A method of compensating for channel power depletion induced by Raman amplification noise in a hybrid distributed Raman amplifier-Erbium doped fiber amplifier. In the method, an equivalent noise figure is determined for a virtual amplifier equivalent to the hybrid distributed Raman amplifier-Erbium doped fiber amplifier, and having an input power equal to the input power of the Erbium doped fiber amplifier when the distributed Raman amplifier is off and an output power equal to the Erbium doped fiber amplifier output power. A compensation power, dependent at least in part upon the equivalent noise figure, is determined. A control signal is provided for controlling the hybrid amplifier such that an optical signal amplified by the hybrid amplifier has a total output power equal to a predetermined nominal output power plus the compensation power.

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 method of monitoring an optical fibre comprises modulating an optical signal with a traffic signal; modulating the optical signal with an incoherent optical frequency domain reflectometry, IOFDR, test signal; transmitting the doubly modulated optical signal onto an optical fibre at a first end of the fibre; detecting scattered radiation output from the first end of the fibre; and analysing the detected scattered radiation using incoherent optical frequency domain reflectometry to determine a distance to a break in the optical fibre. Apparatus suitable for carrying out the method is also described, as well as an optical communications network employing the method.

Abstract: A method of monitoring (200) an optical fiber comprises modulating (210) an optical signal with a traffic signal; modulating (220) the optical signal with an incoherent optical frequency domain reflectometry, IOFDR, test signal; transmitting (230) the doubly modulated optical signal onto an optical fiber at a first end of the fiber; detecting (240) scattered radiation output from the first end of the fiber; and analyzing (250) the detected scattered radiation using incoherent optical frequency domain reflectometry to determine a distance to a break in the optical fiber. Apparatus suitable for carrying out the method is also described, as well as an optical communications network employing the method.

Abstract: A method of monitoring a differential group delay, DGD, of an optical communications signal having a polarisation multiplexed modulation format is described. The method includes the steps of receiving a signal and performing analogue to digital conversion of the signal to generate a digitised signal corresponding to one polarisation of the signal and to generate another digitised signal corresponding to another polarisation of the signal, and applying a polarisation mode dispersion, PMD, compensation to each of the digitised signals. The method further includes the steps of obtaining an indication of the channel transfer function of the optical communications signal, determining a DGD in dependence on the indication of the channel transfer function, determining a delay between the PMD compensated digitised signals, subtracting the delay from the DGD to obtain a corrected DGD, and generating and transmitting a monitoring signal with an indication of the corrected DGD.

Abstract: An optical amplifier for determining the attenuation of a length of optical fiber (7) to which it is adapted to be connected comprising means (5) to receive an input signal from the optical fiber (7), means (6) to output an amplified signal to the optical fiber (7), a gain medium (2) and a pump means (3) arranged to generate the amplified signal from the input signal, the amplifier (1) further comprising means (13) to measure the optical power of the signal leaving the gain medium and means (14) to measure the optical power of the signal backscattered from the optical fiber (7), wherein the pump means (3) is controlled by a control means (4), the control means (4) being adapted to modulate the pump means (3) with a determination signal, the control means (4) being adapted to change the frequency of the determination signal over a plurality of determination frequencies while keeping the amplitude of the determination signal constant, the control means (4) further being adapted to calculate the attenuation of t

Abstract: A wavelength division multiplex optical ring network comprises optical fibre (1-4) arranged in a ring configuration and a plurality of doped fibre optical amplifiers (17-20) arranged in the ring. The spectral response in the ring is configured such in use amplified spontaneous emission (ASE) noise circulates around the ring in a lasing mode to clamp the gain of each doped fibre optical amplifier. Each optical amplifier (17-20) includes respective control means (28) which in use control the optical amplifier to produce a substantially constant output power or to maintain a substantially constant pump power. In the event of loss of the lasing peak, detection means switches the doped fibre optical amplifiers to a different mode of gain control, for example, a mode to produce constant gain at the value before the loss of the lasing peak. Optionally, after a predetermined delay, the optical amplifiers may revert to constant output power or pump power mode.

Abstract: A method of compensating for channel power depletion induced by Raman amplification noise in a hybrid distributed Raman amplifier-Erbium doped fibre amplifier. In the method, an equivalent noise figure is determined for a virtual amplifier equivalent to the hybrid distributed Raman amplifier-Erbium doped fibre amplifier, and having an input power equal to the input power of the Erbium doped fibre amplifier when the distributed Raman amplifier is off and an output power equal to the Erbium doped fibre amplifier output power. A compensation power, dependent at least in part upon the equivalent noise figure, is determined. A control signal is provided for controlling the hybrid amplifier such that an optical signal amplified by the hybrid amplifier has a total output power equal to a predetermined nominal output power plus the compensation power.

Abstract: A method and apparatus for restoration of operating conditions of a WDM optical ring network comprising a plurality of amplifiers linked together in a ring after a break or fault has occurred in the network. The method comprises in response to repair of the break or other fault, increasing output power or/and pump power of an amplifier in the network such that the output power or/and pump power increases substantially in accordance with a ramp function.

Abstract: A method of monitoring (200) an optical fibre comprises modulating (210) an optical signal with a traffic signal; modulating (220) the optical signal with an incoherent optical frequency domain reflectometry, IOFDR, test signal; transmitting (230) the doubly modulated optical signal onto an optical fibre at a first end of the fibre; detecting (240) scattered radiation output from the first end of the fibre; and analysing (250) the detected scattered radiation using incoherent optical frequency domain reflectometry to determine a distance to a break in the optical fibre. Apparatus suitable for carrying out the method is also described, as well as an optical communications network employing the method.