Chirp-compensating transmitter and method

A method of determining a chirp-response function of a laser, comprising:

• modulating the laser with a real-valued double-side-band orthogonal frequency-domain multiplexed (OFDM) signal to yield a characterization optical signal that includes a plurality of subcarriers each including a respective transmitted amplitude and a respective transmitted phase;
• transmitting the characterization optical signal to a coherent-receiver;
• receiving, at the coherent receiver, the characterization optical signal as a chirped-modulated optical signal;
• demodulating the chirped-modulated optical signal to obtain, for each subcarrier of the plurality of subcarriers, a respective received amplitude and a respective received phase;
• and
• for each subcarrier of the plurality of subcarriers, (i) determining a respective chirp-response amplitude of a plurality chirp-response amplitudes of the chirp-response function as a ratio of the respective received amplitude to the respective transmitted amplitude, and (ii) determining a respective chirp-response phase of a plurality chirp-response phases of the chirp-response function as a difference between the respective received phase to the respective transmitted phase.

A chirp-compensating transmitter comprising:

• a signal generator including (i) a processor and (ii) a memory storing machine readable instructions that, when executed by the processor, control the processor to generate a chirp-compensated signal by distorting an original modulated signal according to an inverse of a chirp-response function of a laser, to yield a chirp-compensated signal;
• a laser configured to modulate an amplitude of an optical signal in response to an amplitude of one of (i) the chirp-compensated signal and (ii) a first signal derived therefrom, to yield an amplitude-modulated optical signal;
• and
• a phase modulator disposed downstream of the laser with respect to the optical signal, the phase modulator being configured to modulate a phase of the amplitude-modulated optical signal in response to a phase of one of (i) the chirp-compensated signal and (ii) a second signal derived therefrom.

A method for laser chirp precompensation comprising:

• modulating an amplitude of an optical signal, in response to an amplitude of one of (i) a chirp-compensated signal generated via distortion of an original modulated signal according to an inverse of a chirp-response function of a laser and (ii) a first signal derived from the chirp-compensated signal, to yield an amplitude-modulated optical signal;
• and
• modulating a phase of the amplitude-modulated optical signal in response to a phase of one of (i) the chirp-compensated signal and (ii) a second signal derived from the chirp-compensated signal to yield a chirp-compensated optical signal,
• the chirp-response function being an analytical expression that is a function of a modulation frequency of the original modulation signal and a number of characteristics of the laser that includes at least one of:
• a steady-state value of carrier density, a steady-state value of photon density, a gain compression factor, a characteristic photon life time, a characteristic electron life time, a gain slope constant, and a mode confinement parameter.

A method for laser chirp precompensation comprising:

• distorting an original modulated signal according to the inverse of a chirp-response function of a laser to yield a chirp-compensated signal, said distorting including one of (i) multiplying a frequency-domain representation of the original modulated signal by a frequency-domain representation of the inverse of the chirp-response function, and (ii) convolving a time-domain representation of the original modulated signal by a time-domain representation of the inverse of the chirp-response function;
• modulating an amplitude of an optical signal, in response to an amplitude of one of (i) a chirp-compensated signal generated via distortion of the original modulated signal according to an inverse of the chirp-response function and (ii) a first signal derived from the chirp-compensated signal, to yield an amplitude-modulated optical signal;
• and
• modulating a phase of the amplitude-modulated optical signal in response to a phase of one of (i) the chirp-compensated signal and (ii) a second signal derived from the chirp-compensated signal to yield a chirp-compensated optical signal.