Abstract: Digital data (11) is encoded to a set of five line symbols for optical transmission. The line symbols have amplitude values of 0, ±A1, ±A2, where |A2|>|A1|. A first binary value maps to the line symbols 0 and ±A2 and a second binary value maps to the line symbols ±A1. The amplitude values of the line symbols can be in the ratio A1:A2=1:sqrt(2). At a receiver, the received signal is photodetected to generate an electrical signal which can represent a set of three possible received symbols (RS1, RS2, RS3). Digital data (26) is recovered from the received symbols by comparing the electrical signal with a first amplitude threshold (TH1) and a second amplitude threshold (TH2).

Abstract: A method (100) is disclosed for filtering an optical signal to generate at least one electrical output. The method comprises receiving an optical signal (110) and directing at least a part of the optical signal through an n×m array of wavelength selective elements (120), the n×m array comprising n parallel groups, each group comprising m coupled wavelength selective elements. The method further comprises photodetecting an output from each of the n groups of coupled wavelength selective elements (130), and electrically selecting at least one of the photodetected outputs (140). Also disclosed are an optical filtering module (200, 300) a controller (400) for an optical filtering module and a computer program.

Abstract: Optical transmitter apparatus (100) comprising: a transmitter optical subassembly (130) configured to transmit forward error correction, FEC, codewords on an optical carrier signal; a memory device (110) containing local configuration data; and processing circuitry (120) configured to: receive client signal data and perform FEC encoding on the client signal data to form a sequence of FEC codewords; receive local configuration data from the memory device; obtain a configuration payload pattern of FEC codewords having a FEC code violation and FEC codewords not having a FEC code violation, the configuration payload pattern representing the local configuration data; create FEC code violations within FEC codewords of said sequence according to the configuration payload pattern to form a configuration payload modified sequence of FEC codewords; and provide the configuration payload modified sequence of FEC codewords to the transmitter optical subassembly for transmission.

Abstract: A method for switching data signals transmitted over a transport network is disclosed. The method comprises receiving a plurality of input data signals of a first signal type wherein the plurality of data signals of the first signal type comprises data signals exchanged between a Radio Equipment and a Radio Equipment Controller and aggregating the plurality of input data signals into an aggregated first data signal. The method also comprises receiving a second data signal of a second signal type different to the first signal type, and multiplexing the first data signal with the second data signal to form a combined data signal. The method further comprises forwarding the combined data signal to the transport network. Multiplexing the first data signal with the second data signal comprises, for a frame of the combined data signal, allocating the first data signal to a portion of the frame reserved for the first data signal, and allocating the second data signal to a remaining portion of the frame.

Abstract: An optical system and method for seeding an optical transmitter includes a first optical transmitter comprising a first reflective optical amplifier and a second optical transmitter comprising a second reflective optical amplifier. The second optical transmitter is optically coupled to the first optical transmitter. The optical system also includes an optical cavity for seeding the first reflective optical amplifier with a first optical seed signal. The optical cavity is formed between the first reflective optical amplifier of the first optical transmitter and the second reflective optical amplifier of the second optical transmitter. The first reflective optical amplifier is configured to transmit a first optical signal to the second reflective optical amplifier and the second reflective optical amplifier is configured to provide the first optical seed signal by reflecting a portion of the first optical signal back to the first reflective optical amplifier.

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 first signal is generated from an input signal by a first delay (70), and by low pass filtering (74). A second signal is generated from the input signal and from a second, longer delayed (72), version of the input signal, such that in response to a pulse on the input signal, the second signal has a sequence of two pulses, coinciding respectively with leading and trailing edges of a corresponding pulse on the first signal. If the signals are electrical, they can drive I and Q inputs of an IQ modulator (84, 86). If generated optically, they can be combined directly to produce the encoded optical output signal. By using such delays and filtering to produce these signals, a CAPS-3 encoded optical signal can be simulated, to obtain its chromatic dispersion tolerance advantages with less complex hardware and less power consumption.

Abstract: A first signal is generated from an input signal by a first delay (70), and by low pass filtering (74). A second signal is generated from the input signal and from a second, longer delayed (72), version of the input signal, such that in response to a pulse on the input signal, the second signal has a sequence of two pulses, coinciding respectively with leading and trailing edges of a corresponding pulse on the first signal. If the signals are electrical, they can drive I and Q inputs of an IQ modulator (84, 86). If generated optically, they can be combined directly to produce the encoded optical output signal. By using such delays and filtering to produce these signals, a CAPS-3 encoded optical signal can be simulated, to obtain its chromatic dispersion tolerance advantages with less complex hardware C and less power consumption.

Abstract: A transmitter (1) is configured to transmit an optical signal, the transmitter comprising an optical dispersion compensator (10) configured to compensate for chromatic dispersion of the optical signal. The optical dispersion compensator comprises a plurality of delay elements (20; 40). The plurality of delay elements (20; 40) have a combined response providing a delay to the transmitted optical signal which varies with frequency.

Abstract: A method for managing traffic of a plurality of packets in a plurality of packet flows transmitted using a time-slotted interface. The packet flows traverse a plurality of switches of a transport network according to an assigned path from a source node to a destination node. The method comprises determining an end-to-end latency of a plurality of packets traversing a current switch in packet flows and assigning priority values to the packets traversing the current switch, wherein a priority value of a packet depends on the determined end-to-end latency of said packets. The method further comprises allocating a time slot in an output interface of the current switch to the packet having the highest priority value among the packets competing for said time slot.

Abstract: A method in a first level aggregation node of a transport network is disclosed. The transport network comprises the first level aggregation node, a second level aggregation node and a Passive Optical Network. T the method comprises receiving, from the second level aggregation node, a plurality of wavelength division multiplexing (WDM) channels having wavelengths in a first spectrum section and generating at least one passive optical channel having a wavelength in a second spectrum section, different to the first spectrum section. The method further comprises combining at least some of the WDM channels received from the second level aggregation node with the at least one passive optical channel, and forwarding the combined WDM channels and passive optical channel to a termination node in the Passive Optical Network. Also disclosed are a method in a termination node of a transport network, a first level aggregation node, a termination node and a computer program.

Abstract: A method for managing traffic of a plurality of packets in a plurality of packet flows transmitted using a time-slotted interface. The packet flows traverse a plurality of switches of a transport network according to an assigned path from a source node to a destination node. The method comprises determining (202) an end-to-end latency of a plurality of packets traversing a current switch in packet flows and assigning (204) priority to packets to the packets traversing the current switch, wherein a priority value of a packet depends on the determined end-to-end latency of said packets. The method further comprises allocating (206) a time slot in an output interface of the current switch to the packet having the highest priority value among the packets competing for said time slot.

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 transmitting communications traffic, the method comprising steps of receiving a sequence of communications traffic bits; and mapping the sequence of communications traffic bits onto a respective one of a plurality of transmission symbols for transmission during a symbol time. Each transmission symbol is identified by a respective first symbol identifier indicative of a respective one or more of a plurality, M, of wavelengths for a transmission signal and a respective second symbol identifier indicative of a respective one or more of a plurality, N, of optical fibers on which to transmit the transmission signal.

Abstract: An optical node (100) is disclosed. The optical node (100) comprises first and second line ports (104, 106) for Wavelength Division Multiplexing (WDM) signals and first and second pluralities of local add/drop ports (108, 110) for optical signals. The optical node further comprises a wavelength selective switch (112), coupled between the first and second line ports (104, 106) and configured to drop optical signals from a WDM signal traversing the optical node between the first and second line ports (104, 106), and a node optical combiner (114) coupled between the first and second line ports (104, 106) and configured to add optical signals to a WDM signal traversing the optical node between the first and second line ports (104, 106).

Abstract: Techniques are disclosed for determining propagation delay of a first path and or of a second path which connect a first transceiver unit associated with a first clock to a second transceiver unit associated with a second clock in a communications network, based on a first time reference representing a time of transmission of a first signal from the first transceiver unit, a second time reference representing the time of receipt of the first signal at the second transceiver unit, a third time reference representing a time of transmission of a reply to the second signal from the second transceiver unit, and a fourth time reference representing the time of receipt of the reply to the second signal at the first transceiver unit.

Abstract: A method for managing traffic of a plurality of packets in a plurality of packet flows transmitted using a time-slotted interface. The packet flows traverse a plurality of switches of a transport network according to an assigned path from a source node to a destination node. The method comprises determining (202) an end-to-end latency of a plurality of packets traversing a current switch in packet flows and assigning (204) priority to packets to the packets traversing the current switch, wherein a priority value of a packet depends on the determined end-to-end latency of said packets. The method further comprises allocating (206) a time slot in an output interface of the current switch to the packet having the highest priority value among the packets competing for said time slot.

Abstract: A method for switching data signals transmitted over a transport network is disclosed. The method comprises receiving a plurality of input data signals of a first signal type wherein the plurality of data signals of the first signal type comprises data signals exchanged between a Radio Equipment and a Radio Equipment Controller and aggregating the plurality of input data signals into an aggregated first data signal. The method also comprises receiving a second data signal of a second signal type different to the first signal type, and multiplexing the first data signal with the second data signal to form a combined data signal. The method further comprises forwarding the combined data signal to the transport network. Multiplexing the first data signal with the second data signal comprises, for a frame of the combined data signal, allocating the first data signal to a portion of the frame reserved for the first data signal, and allocating the second data signal to a remaining portion of the frame.

Abstract: A method (10) of encapsulating digital communications signals for transmission on a communications link, comprising steps: a. receiving a first signal of a first signal type and comprising a first clock signal and receiving a second signal of a second signal type, different to the first, and comprising a second clock signal different to the first clock signal, each clock signal having a respective clock value and accuracy (12); b. obtaining the first clock signal (14); c. obtaining a difference between at least one of the clock values of the clock signals and the accuracies of the clock signals (16) and buffering the second signal for a time at least long enough to compensate for the difference (18); and d. assembling the first signal and the buffered second signal into a frame comprising an overhead and a payload comprising a first portion and a second portion, mapping the first signal into the first portion and the second signal into the second portion (20), wherein step d.