Abstract: A method (100) of encoding communications traffic bits onto an optical carrier signal in a pulse amplitude modulation, PAM, format. The method comprises: receiving (102) bits to be transmitted; receiving (104) an optical carrier signal comprising optical pulses having an amplitude and respective phases; performing (106) PAM of the optical pulses to encode at least one respective bit in one of a pre-set plurality of amplitudes of a said optical pulse; and performing (108) phase modulation of the optical pulses to encode at least one further respective bit in a phase difference between a said optical pulse and a consecutive optical pulse.

Abstract: Methods in an optical receiver, for decoding a received M-level pulse-amplitude-modulated, PAM-M, optical signal. An example method comprises, for a first interval, decoding (510) the received PAM-M optical signal using a standard PAM-M decoder with M-1 thresholds, using first sampling times, to obtain a first set of decoded bits, and decoding (520) the received PAM-M optical signal using a duobinary decoder with 2M-2 thresholds, at second sampling times offset from the first sampling times, to obtain second set of decoded bits. The method further comprises calculating (530) first and second error metrics corresponding to the first and second sets of decoded bits, respectively, and selecting (540) the standard PAM-M decoder or the duobinary decoder for subsequent decoding of the received PAM-M optical signal, based on the first and second error metrics.

Abstract: Quantum bit decoding apparatus, configured to receive a photon having a qubit encoded in a property of the photon has a demodulation apparatus. The demodulation apparatus includes an optical modulator to randomly apply one of a plurality of modulation values for decoding the qubit to the property of the photon and an optical router to route the photon according to the qubit. The decoding apparatus has an optical delay apparatus having an optical combiner, a first optical path, from the optical router to the optical combiner and a second optical path, from the optical router to the optical combiner. The second path has a different optical path length from the first path. The decoding apparatus has a detection apparatus to detect a photon and to determine whether a detected photon is delayed relative to a reference time and to determine the qubit according to the determined delay.

Abstract: A path computation engine, PCE, (100) for an optical communications network comprising a plurality of nodes and a plurality of links.

Abstract: A receiver module (100) is disclosed for receiving an optical input signal and generating an electrical output signal from the optical input signal. The receiver module comprises an input (110) for receiving an optical input signal and a polarising beam splitter (120) for splitting one of the optical input signal and a local recovery optical signal. The receiver module also comprises a multiport optical coupler (130) for coupling the outputs of the polarisation beam splitter and the other of the optical input signal and local recovery optical signal and outputting a plurality of outputs. The receiver module further comprises a first photodetector unit (140) for individually photodetecting the outputs of the multiport optical coupler and an optical modulation unit (150) for using each of the photodetected outputs to modulate a respective local conversion optical signal, where each local conversion optical signal has a different frequency from the other local conversion optical signals.

Abstract: A method (100) of encoding communications traffic bits onto an optical carrier signal in a pulse amplitude modulation, PAM, format. The method comprises: receiving (102) bits to be transmitted; receiving (104) an optical carrier signal comprising optical pulses having an amplitude and respective phases; performing (106) PAM of the optical pulses to encode at least one respective bit in one of a pre-set plurality of amplitudes of a said optical pulse; and performing (108) phase modulation of the optical pulses to encode at least one further respective bit in a phase difference between a said optical pulse and a consecutive optical pulse.

Abstract: A receiver module (100) is disclosed for receiving an optical input signal and generating an electrical output signal from the optical input signal. The receiver module comprises an input (110) for receiving an optical input signal and a polarising beam splitter (120) for splitting one of the optical input signal and a local recovery optical signal. The receiver module also comprises a multiport optical coupler (130) for coupling the outputs of the polarisation beam splitter and the other of the optical input signal and local recoveiy optical signal and outputting a plurality of outputs. The receiver module further comprises a first photodetector unit (140) for individually photodetecting the outputs of the multiport optical coupler and an optical modulation unit (150) for using each of the photodetected outputs to modulate a respective local conversion optical signal, where each local conversion optical signal has a different frequency from the other local conversion optical signals.

Abstract: A path computation engine, PCE, (100) for an optical communications network comprising a plurality of nodes and a plurality of links.