Telefonaktiebolaget Lm Ericsson (publ)

Ericsson Ab

Marconi Communications Gmbh

Enrico Forestieri

Marco Secondini

Giulio Colavolpe

Fabio Cavaliere

Giancarlo Prati

Luca Poti

Roberto Magri

Tommaso Foggi

Domenico Marsella

Gianluca Meloni

Antonio Malacarne

Francesco Fresi

Tommaso Catuogno

A method () of encoding communications traffic bits onto an optical carrier signal in a pulse amplitude modulation, PAM, format. The method comprises: receiving () bits to be transmitted; receiving () an optical carrier signal comprising optical pulses having an amplitude and respective phases; performing () 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 () 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.

Encoding and decoding communications traffic in a pulse amplitude modulation format and optical apparatus for same

Digital data () is encoded to a set of five line symbols for optical transmission. The line symbols have amplitude values of 0, &#xb1;A1, &#xb1;A2, where |A2|&#x3e;|A1|. A first binary value maps to the line symbols 0 and &#xb1;A2 and a second binary value maps to the line symbols &#xb1;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 () is recovered from the received symbols by comparing the electrical signal with a first amplitude threshold (TH1) and a second amplitude threshold (TH2).

Line coding for optical transmission

A first signal is generated from an input signal by a first delay (), and by low pass filtering (). A second signal is generated from the input signal and from a second, longer delayed (), 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 (). 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.

Encoding for optical transmission

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.

Method of transmitting communications traffic, transmitter and communications transmission system

A method () of non-linear propagation impairment equalization, the method comprising the steps of: a. receiving () communications traffic carried by an optical communications signal transmitted over an optical communications link; b. generating () a time dependent filter representation of a nonlinear time-variant impulse response of the inverse of the optical communications link; and c. applying () the time dependent filter representation to the received communications traffic to form non-linear propagation impairment equalized communications traffic. An optical communications link nonlinear propagation impairment equalizer and optical communications signal receiver apparatus are also provided.

Non-linear propagation impairment equalization

A method of detecting a signal in an optical receiver is described. The method includes converting a received optical signal to a digital electrical signal comprising a plurality of samples, applying a predetermined phase rotation to said samples to obtain amplitude and phase components of phase range adjusted sample values, and performing a first detection process based on the amplitude and phase components of the phase range adjusted sample values.

Receiver for optical transmission system

An equalizer () processes, in the electrical domain, a signal obtained from a path of an optical transmission system. The equalizer comprises N cascaded stages (where N&#x2267;1). At least one of the stages comprises a cascade of a linear equalization element () and a non-linear equalization element (). The equalizer () is able to compensate for both linear impairments, such as dispersion, and non-linear impairments. The cascaded linear and non-linear elements can simulate the effect of signal propagation through a fiber which has the opposite propagation parameters (e.g. attenuation, dispersion, non-linearity) to those of the propagation path experienced by a signal in the transmission system. The non-linear equalization element () can be a non-linear phase rotator which rotates phase of an input signal proportional to the squared modulus of the input signal amplitude. The linear equalization element () can comprise a digital filter, such as an Infinite Impulse Response (HR) filter or a Finite Impulse Response (FIR) filter.

Equalizer for an optical transmission system

A method () of compensating phase noise in a coherent optical communications network. The method comprises: receiving a traffic sample (); receiving an optical carrier and determining a phase noise estimate for the optical carrier (); and removing the phase noise estimate from the traffic sample to form a phase noise compensated traffic sample ().

Phase noise compensation in coherent optical communications systems

A method of and a receiver() for detection of a received signal in an optical fiber communication system using Viterbi algorithm methodology in which branch metrics are obtained using approximated expressions to calculate the branch metrics. Use of the expressions results in practically the same performance as a receiver based on exact metrics.

Maximum likelihood sequence estimation in optical fibre communication systems

A polarization multiplex transmission system () comprises two optical signals (z, z) transmitted over the same optical fiber () at the same wavelength but with orthogonal polarizations. The system is characterized by receiving apparatus () which is operable to filter the two components with orthogonal polarization of the signal received in accordance with an appropriate transfer matrix which is dynamically controlled on the basis of the output signals in such a manner as to approximate the reverse transfer matrix of the fiber in the region of the spectrum occupied by the signal so as to compensate for Polarization Mode Dispersion (PMD) and polarization rotation introduced by the fiber and eliminating distortion and mutual interference effects for both the signals and thereby obtain a demultiplexed output corresponding to the two transmitted signals.

System, method and apparatus for polarization mode dispension compensation and demultiplexing polarization multiplexed signals

A method for the adaptive adjustment of a PMD compensator in optical fiber communication systems comprises the steps of taking the signal at the compensator output and extracting the components y(t) and y(t) on the two orthogonal polarizations, computing the signal y(t)=[y(t)]+[y(t)], sampling the signal y(t) at instants t=kT with T=symbol interval to obtain samples y(t), computing the mean square error e(k)=y(t)&#x2212;u(k) with u(k) equal to the symbol transmitted, and adjusting the parameters of the compensator to seek to minimize e(k). A PMD compensator in accordance with the method comprises an adjustment system which comprises in turn a photodetecor () which takes the components y(t) and y(t) on the two orthogonal polarizations from the signal at the compensator output, a sampler () which samples at instants t=kT with T=symbol interval, the signal y(t)=[y(t)]+[y(t)]at the output of the photodetector () to obtain samples y(t), a circuit () for computation of the mean square error e(k)=y(t)&#x2212;u(k) with u(k) equal to the symbol transmitted, and a regulator () which regulates the parameters of the compensator to seek to minimize e(k).

Polarisation mode dispersion compensator using a mean square error technique

A method for the adaptive adjustment of a PMD compensator in optical fiber communication systems with the compensator comprising a cascade of adjustable optical devices through which passes an optical signal to be compensated and comprising the steps of computing the Stokes parameters S, S, S, Sin a number Q of different frequencies of the signal output from the compensator, producing control signals for parameters of at least some of said adjustable optical devices so as to make virtually constant said Stokes parameters computed at different frequencies. A compensator comprising a cascade of adjustable optical devices (-) through which passes an optical signal to be compensated, an adjustment system which takes the components y(t) e y(t) on the two orthogonal polarizations from the signal at the compensator output, and which comprises a controller () which on the basis of said components computes the Stokes parameters S, S, S, Sin a number Q of different frequencies of the signal output by the compensator and which emits control signals for at least some of said adjustable optical devices so as to make virtually constant the Stokes parameters computed at the different frequencies.

Method based on stokes parameters for the adaptive adjustment of PMD compensators in optical fiber communication systems and compensator in accordance with said method

A coding scheme of order n for digital communications, in particular optical communication, for obtaining a coded signal x(t) which represents binary data which are constituted by sequences of information bits {u} with rate T, the scheme having N=2states, named &#x3a3;, for i=1, 2, . . . , N, and comprising predetermined elementary signals s(t) which are combined in the signal x(t). According to the scheme, if, at the time t=kT, the coding is in a state &#x3a3;of the N states, the arrival of the information bit uof the sequence {u} forces a transition to the state &#x3a3;of the N states and the selection of the elementary signal s(t) as x(t), where q and i are given by the following equations: d=m&#x2212;1 mod 2; d=d+umod 2; y=2(m&#x2212;1)+d; q=(r mod N)+1; and i=r+1 if r&#x3c;N, or i=r&#x2212;2N otherwise.

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Parma, Italy

Enrico Forestieri