Non-linearity compensation in an optical transmission

A transmitter for use in transmitting information over a non-linear optical channel, the transmitter comprising:

• a digital data input port;
• a signal generator, adapted to generate an electrical information signal comprising a plurality of closely-spaced sub-carriers in a frequency domain, and which encodes a digital data sequence received at the digital data input port;
• means for generating a phase modulation which is a function of an instantaneous value of a transmitted optical power characteristic corresponding with said electrical information signal, the function being selected such that the effect of nonlinearity of the optical channel is mitigated;
• an optical source for generating an optical carrier wave;
• a first optical modulator arranged to apply the electrical information signal to said optical carrier wave;
• and
• a second optical modulator arranged to apply the phase modulation to said optical carrier wave to generate a pre-compensated transmitted optical signal.

A receiver for use in receiving information that has been transmitted over a non-linear optical channel, the receiver comprising:

• an optical detector arranged to detect a received optical signal comprising said information transmitted over the non-linear optical channel, to produce a corresponding received time-varying electrical signal comprising a plurality of closely-spaced sub-carriers in a frequency domain;
• means for determining a phase modulation which is a function of an instantaneous value of a received optical power characteristic corresponding with said received optical signal, the function being selected such that the effect of nonlinearity of the optical channel is mitigated;
• at least one phase-modulation means arranged to multiply said received electrical signal by said phase modulation to produce a phase-modulated received signal;
• and
• a signal decoder adapted to recover the transmitted information from the phase-modulated received signal.

A method of transmitting information over a nonlinear optical channel, comprising the steps of:

• receiving a digital data input sequence;
• generating an electrical information signal comprising a plurality of closely spaced subcarriers in a frequency domain, and which encodes the digital data input sequence;
• generating a pre-compensated electrical signal by multiplying the electrical information signal with a phase modulation which is a first function of an instantaneous value of a transmitted optical signal power corresponding with the electrical information signal, the first function being selected such that the effect of nonlinearity of the optical channel is mitigated;
• and
• modulating an optical source with the pre-compensated electrical signal to generate a corresponding pre-compensated transmitted optical signal.

A transmitter for use in transmitting information over a non-linear optical channel, the transmitter comprising:

• a digital data input port;
• a signal generator, adapted to generate an electrical information signal comprising a plurality of closely-spaced sub-carriers in a frequency domain, and which encodes a digital data sequence received at the digital data input port;
• means for generating a precompensated electrical signal by multiplying the electrical information signal with a phase modulation which is a function of an instantaneous value of a transmitted optical power characteristic corresponding with said electrical information signal, the function being selected such that the effect of nonlinearity of the optical channel is mitigated;
• an optical source for generating an optical carrier wave;
• and
• an optical modulator arranged to apply the pre-compensated electrical signal to the optical carrier wave.