Abstract: An optical network (1) comprising an optical network element (10) comprising a first optical transmitter (14), a first controller (16), a first optical receiver and a second optical receiver and a second optical network element (12). There is provided a transmission path (30) between said first optical network element and said second optical network element. Said first optical transmitter is arranged to generate and transmit a first optical signal. Said first controller is arranged to control said first optical transmitter to generate and transmit said first optical signal at a wavelength selected from a predetermined plurality of wavelengths. Said first optical receiver is arranged to detect a backscatter portion of said first optical signal returned to said first optical network element along said transmission path by distributing scattering.

Abstract: A reflective optical network (10) comprises an optical network unit (14) and an optical receiver (22). The optical network unit (14) comprises a reflective optical modulator (16) arranged to receive a seed optical signal, and a transmitter controller (18) arranged to receive a data signal (20) and to control the modulator (16) to apply the data signal (20) to the seed optical signal, to form an optical data signal. The transmitter controller (18) is arranged to process the data signal (20) to substantially prevent the optical data signal comprising spectral components at frequencies lower than a cut-off frequency, being the frequency at which a power spectral density of said optical data signal is lower than a peak power spectral density of said optical signal by a cut-off power value. The optical receiver (22) comprises an electrical domain high pass filter (26) having a cut-off frequency higher than a linewidth of the seed optical signal.

Abstract: An optical network unit (10) comprising a reflective semi-conductor optical amplifier (R-SOA) 12 and a driver 14. The R-SOA has a large optical confinement factor and is arranged to receive a portion of a downstream optical signal having a signal wavelength and a signal power. The driver is arranged to generate a drive signal 16 to drive the R-SOA. The drive signal is arranged to cause the R-SOA to operate in saturation at the signal power. The drive signal is further arranged to cause the R-SOA to apply a return-to-zero line code to said portion of the downstream optical signal to form an upstream optical signal at the signal wavelength. The drive signal is further arranged to cause the R-SOA to apply a phase modulation to the upstream optical signal.

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: Optical transmitter apparatus 10 comprising a reflective optical amplifier 12, a driver 14, an optical splitter 16, polarisation compensation apparatus 18 and an optical router 20. The reflective optical amplifier is arranged to receive an optical seed signal. The driver is arranged to generate a drive signal arranged to cause the reflective optical amplifier to amplify the optical seed signal to form an optical signal. The optical splitter is arranged to receive the optical signal and to split off a part of the optical signal to form a further optical signal. The polarisation compensation apparatus is arranged to receive the further optical signal and to rotate a polarisation of the further optical signal by a pre-determined amount, to form a further optical seed signal. The optical router is arranged to receive the further optical seed signal and to direct the further optical seed signal to the reflective optical amplifier for amplification thereby.

Abstract: A distribution node of a passive optical network (PON) comprises a first port for receiving a first optical continuous envelope modulated downstream data signal at a first wavelength (?C) from a first optical line termination unit (OLT1) and a second port for receiving a second optical continuous envelope modulated downstream data signal at a second wavelength (?L) from a second optical line termination unit (OLT2). A first converter (FBG-1) performs continuous envelope modulation-to-intensity modulation conversion of the first optical downstream data signal and forwards the converted first optical downstream data signal (?C) to the first group of optical network units (ONU1 . . . N). A second converter (FBG-2) performs continuous envelope modulation-to-intensity modulation conversion of the second optical downstream data signal and forwards the converted second optical downstream data signal (?L) to the second group of optical network units (ONUN+1 . . . 2N).

Abstract: A free space optical communications link node 10 comprising transmitter apparatus 12 comprising a first optical transmitter 14, arranged to transmit high priority traffic on a first upstream optical signal having a first wavelength and at a first optical signal power, and a second optical transmitter 16 arranged to transmit low priority traffic on a second upstream optical signal having a second wavelength, different to the first wavelength, and at a second optical signal power. The node 10 further comprises receiver apparatus 18 comprising a first optical amplifier 20 arranged to receive and amplify a first downstream optical signal having a third wavelength and carrying high priority traffic and a second downstream optical signal having a fourth wavelength, different to the third wavelength, and carrying low priority traffic.

Abstract: The invention relates to improvements in or relating to modulation in an Optical Network, and to an apparatus, a method and a communications network for modulation in an Optical Network. An apparatus is arranged to receive a modulated optical signal comprising a carrier wavelength and first data. The apparatus is arranged to substantially erase the first data from the optical signal by performing an inversion operation on the modulated optical signal. The apparatus is arranged to receive second data and to modulate the carrier wavelength with the second data for onward transmission of the second data. The inversion operation comprises applying a signal comprising an inverse of the first data to at least a portion of the modulated optical signal. The signal may further comprise the second data such that the modulation of the carrier wavelength and erasure of the first data is performed in a single operation.

Abstract: An optical PON network comprises a central office which generates N DPSK modulated optical signals, where N is an integer greater than 1, an optical coupling which connects the N signals to at least one optical fiber, a passive distribution node located remotely from the central office which has at least one input port that is coupled to the fiber and a plurality of output ports, the node being arranged to transmit a first wavelength of the N signals to at least one of its output ports, and at least one optical network unit connected through a respective optical fiber to the first output port of the passive distribution node. The passive distribution node comprises an arrayed waveguide grating which provides a passive optical connection between its input port and the first output port and which for that connection functions as a bandpass filter having a profile and bandwidth selected such that the DPSK optical signal passed to the input node is converted to an intensity modulated signal at the output port.

Abstract: Methods and apparatus for determining transmission power of a plurality of optical channels for transmission of the channels along respective paths obtained through an optical transmission system. Information is obtained indicative of the path of each channel through the optical transmission system, and each channel is allocated to a group of channels in dependence upon the obtained information. A quality metric is determined for each group of channels, and a total transmission power for each group is determined in dependence upon the determined quality metric.

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 network (1) comprising an optical network element (10) comprising a first optical transmitter (14), a first controller (16), a first optical receiver and a second optical receiver and a second optical network element (12). There is provided a transmission path (30) between said first optical network element and said second optical network element. Said first optical transmitter is arranged to generate and transmit a first optical signal. Said first controller is arranged to control said first optical transmitter to generate and transmit said first optical signal at a wavelength selected from a predetermined plurality of wavelengths. Said first optical receiver is arranged to detect a backscatter portion of said first optical signal returned to said first optical network element along said transmission path by distributing scattering.

Abstract: A reflective optical network (10) comprises an optical network unit (14) and an optical receiver (22). The optical network unit (14) comprises a reflective optical modulator (16) arranged to receive a seed optical signal, and a transmitter controller (18) arranged to receive a data signal (20) and to control the modulator (16) to apply the data signal (20) to the seed optical signal, to form an optical data signal. The transmitter controller (18) is arranged to process the data signal (20) to substantially prevent the optical data signal comprising spectral components at frequencies lower than a cut-off frequency, being the frequency at which a power spectral density of said optical data signal is lower than a peak power spectral density of said optical signal by a cut-off power value. The optical receiver (22) comprises an electrical domain high pass filter (26) having a cut-off frequency higher than a linewidth of the seed optical signal.

Abstract: All-optical phase-modulated data signal regenerator apparatus (10) comprising an optical input (12), an optical signal converter (16), an optical carrier signal source (18), optical signal forming apparatus (20) and an optical output (14). The input (12) is arranged to receive a phase-modulated optical data signal. The signal converter (16) is arranged to receive the data signal and to convert phase modulation of the data signal into a corresponding intensity modulation of an intermediate optical signal. The carrier signal source (18) provides an optical carrier signal.

Abstract: A distribution node of a passive optical network (PON) comprises a first port for receiving a first optical continuous envelope modulated downstream data signal at a first wavelength (?C) from a first optical line termination unit (OLT1) and a second port for receiving a second optical continuous envelope modulated downstream data signal at a second wavelength (?L) from a second optical line termination unit (OLT2). A first converter (FBG-1) performs continuous envelope modulation-to-intensity modulation conversion of the first optical downstream data signal and forwards the converted first optical downstream data signal (?C) to the first group of optical network units (ONU1 . . . N). A second converter (FBG-2) performs continuous envelope modulation-to-intensity modulation conversion of the second optical downstream data signal and forwards the converted second optical downstream data signal (?L) to the second group of optical network units (ONUN+1 . . . 2N).

Abstract: An optical network unit (10) comprising a reflective semi-conductor optical amplifier (R-SOA) 12 and a driver 14. The R-SOA has a large optical confinement factor and is arranged to receive a portion of a downstream optical signal having a signal wavelength and a signal power. The driver is arranged to generate a drive signal 16 to drive the R-SOA. The drive signal is arranged to cause the R-SOA to operate in saturation at the signal power. The drive signal is further arranged to cause the R-SOA to apply a return-to-zero line code to said portion of the downstream optical signal to form an upstream optical signal at the signal wavelength. The drive signal is further arranged to cause the R-SOA to apply a phase modulation to the upstream optical signal.

Abstract: The invention relates to improvements in or relating to modulation in an Optical Network, and to an apparatus, a method and a communications network for modulation in an Optical Network. An apparatus is arranged to receive a modulated optical signal comprising a carrier wavelength and first data. The apparatus is arranged to substantially erase the first data from the optical signal by performing an inversion operation on the modulated optical signal. The apparatus is arranged to receive second data and to modulate the carrier wavelength with the second data for onward transmission of the second data. The inversion operation comprises applying a signal comprising an inverse of the first data to at least a portion of the modulated optical signal. The signal may further comprise the second data such that the modulation of the carrier wavelength and erasure of the first data is performed in a single operation.

Abstract: An optical transmitter apparatus for use in an optical communications network has a polarization dithering unit, an optical transmitter unit, and a transmission fiber. The polarization dithering unit is connected in series between an output of the optical transmitter unit and the transmission fiber.

Abstract: A passive optical network system, a line coding method and an optical network unit are described. The optical network unit comprises a downlink optical receiver configured to receive a first portion of a downstream data signal, and an uplink optical remodulator configured to receive a second portion of the downstream data signal and remodulate it to generate a return-to-zero line coded upstream data signal. The downstream data signal may be inverse-return-to-zero line coded.

Abstract: An iterative method for power pre-emphasis of N optical channels in a Wavelength Division Multiplex (WDM) signal in an optical communication systems in accordance with which representative Xi characteristics are defined for the channels with among the characteristics there being included at least one characteristic that is a function of the Bit Error Rate (BER).