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 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 method for dual polarisation optical transmission is disclosed. The method comprises splitting a continuous wave light source into first and second sub-channels, optically modulating each sub-channel with a data signal, and superimposing a first pilot tone onto the first optically modulated sub-channel and a second pilot tone, different from the first pilot tone, onto the second optically modulated sub-channel. The method further comprises polarisation multiplexing the first and second sub-channels to form a polarisation multiplexed signal, in which the first and second sub-channels have orthogonal states of polarisation, and transmitting the polarisation multiplexed signal.

Abstract: An optical transmission method (10) comprising steps of receiving (12) a communication signal comprising symbols for transmission. The method comprises performing (16) linear amplitude modulation of an optical carrier with the communication signal to generate an amplitude modulated optical carrier. The method comprises performing low-pass filtering (14) to reduce a bandwidth of the symbols to less than a Nyquist bandwidth of the symbols. The method comprises transmitting (18) the amplitude modulated optical carrier. The method further comprises receiving (20) the amplitude modulated optical carrier following transmission and performing direct detection of the received amplitude modulated optical carrier to generate a received electrical signal; and determining (22) received symbols from the received electrical signal using an indication of a nonlinear impulse response of the direct detection.

Abstract: A method for dual polarisation optical transmission is disclosed. The method comprises splitting a continuous wave light source into first and second sub-channels, optically modulating each sub-channel with a data signal, and superimposing a first pilot tone onto the first optically modulated sub-channel and a second pilot tone, different from the first pilot tone, onto the second optically modulated sub-channel. The method further comprises polarisation multiplexing the first and second sub-channels to form a polarisation multiplexed signal, in which the first and second sub-channels have orthogonal states of polarisation, and transmitting the polarisation multiplexed signal.

Abstract: An optical transmission method (10) comprising steps of receiving (12) a communication signal comprising symbols for transmission. The method comprises performing (16) linear amplitude modulation of an optical carrier with the communication signal to generate an amplitude modulated optical carrier. The method comprises performing low-pass filtering (14) to reduce a bandwidth of the symbols to less than a Nyquist bandwidth of the symbols. The method comprises transmitting (18) the amplitude modulated optical carrier. The method further comprises receiving (20) the amplitude modulated optical carrier following transmission and performing direct detection of the received amplitude modulated optical carrier to generate a received electrical signal; and determining (22) received symbols from the received electrical signal using an indication of a nonlinear impulse response of the direct detection.

Abstract: A method of controlling a parameter in the generation of a coherent optical signal, the method comprising the steps of: receiving a set of signal samples relating to detection of a coherent optical signal; transforming the set of signal samples into a set of spectrum samples in the frequency domain, the set of spectrum samples being an estimation of the spectrum of the coherent optical signal; calculating at least one feedback variable based on the spectrum samples; and adjusting the parameter based on the at least one feedback variable.

Abstract: A method of controlling a parameter in the generation of a coherent optical signal, the method comprising the steps of: receiving a set of signal samples relating to detection of a coherent optical signal; transforming the set of signal samples into a set of spectrum samples in the frequency domain, the set of spectrum samples being an estimation of the spectrum of the coherent optical signal; calculating at least one feedback variable based on the spectrum samples; and adjusting the parameter based on the at least one feedback variable.

Abstract: A 2n quadrature amplitude modulation optical modulator has an optical input for receiving an optical signal. A first splitter is coupled to the optical input and has first and second outputs. A first optical modulation apparatus, coupled to the first output, applies a modulation scheme having 2n-2 constellation points to produce a first modulated optical signal representing an in-phase component. A second optical modulation apparatus, coupled to the second output, applies a modulation scheme having 2n-2 constellation point to produce a second modulated optical signal representing a quadrature component. An optical combiner combines the first and second modulated optical signals to produce an output modulated optical signal which is modulated with a modulation scheme having 2n constellation points.

Abstract: An analogue to digital converter is arranged to receive and process an analogue optical input signal to produce an N bit digital optical output signal quantised to 2N levels, where N is greater than or equal to 2. The converter has an input for receiving the optical input signal and N processing channels which are each coupled to the input, at least one of said processing channels comprising an optical processing circuit arranged to generate a plurality of digital optical output signals. The optical processing circuit is arranged to change the state of each digital optical output signal corresponding to a respective different value of the analogue optical input signal, and an optical combining circuit for combining the optical output signals in order to generate one bit of the N-bit digital optical signal.

Abstract: An analogue to digital converter (100) is arranged to receive and process an analogue optical input signal (110) to produce an N bit digital optical output signal (140) quantised to 2N levels, where N is greater than or equal to 2. The converter (100) has an input (115) for receiving the optical input signal (110) and N processing channels (131, 132, 133) which arc each coupled to the input, at least one of said processing channels comprising an optical processing circuit (201, 202, 203, 204, 205, 206, 207) arranged to generate a plurality of digital optical output signals. The optical processing circuit is arranged to change the state of each digital optical output signal corresponding to a respective different value of the analogue optical input signal, and an optical combining circuit (301, 302, 303, 304) for combining the optical output signals in signal order to generate one bit of the N-bit digital optical signal.

Abstract: Improvements in or relating to Optical Networks. The invention relates to improvements in or relating to optical networks, and methods and an apparatus for providing communications services. Receiving an optical signal is described comprising a carrier wavelength and optical data. The optical data is substantially erased, and the carrier wavelength is re-modulated with user data for onward transmission of the user data.