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: 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: 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: 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: The invention relates to improvements in or relating to optical networks. Methods and apparatus are disclosed for providing communications services to at least one user. Transmission of an optical signal in the downstream direction is described comprising at least one Wavelength Division Multiplexing channel such that at least one of the channels is an unmodulated channel. The unmodulated channel is arranged to transmit user data from the at least one user in the upstream direction.

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 fibre, a passive distribution mode located remotely from the central office which has at least one input port that is coupled to the fibre and a plurality of output 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 fibre 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: Optical signal processing apparatus for processing packetised optical signals comprising a probe signal generator which is arranged to issue a plurality probe pulses, and an optical AND logic gate assembly, the arrangement of the apparatus being such that, in use, the probe signals have an interval between pulses substantially equal to the interval between data elements of the packetised data to be extracted, and the packetised data and the probe pulses are then combined by the AND logic gate assembly.