Pre-shaping laser modulation signals to increase modulation index

A communication node, comprising:

• a modulator that receives an output signal and provides therefrom a first modulated laser beam, and
• a demodulator that receives a second modulated laser beam and provides therefrom an input signal;
• wherein
• the modulator includes a pre-shaper that is configured to transform large excursions of the output signal differently than smaller excursions of the output signal, to thereby increase a modulation index associated with the first modulated signal, and
• the demodulator includes:
• a detector that converts the second modulated laser beam to an electronic signal, and
• a post-shaper that is configured to transform particular excursions of the electronic signal differently than other excursions of the electronic signal, to form the input signal.

A communication system, comprising:

• a network of optical fibers;
• a first node of the communication system, including:
• a source that provides an electronic output signal having high frequency positive and negative excursions in amplitude with respect to an average amplitude with some excursions being larger than other excursions;
• a pre-shaper that transforms the output signal to form a transformed output signal, including reducing the amplitude of larger negative excursions with respect to other excursions in the output signal so as to increase a modulation index;
• means to bias the transformed output signal to form a biased and transformed output signal so that a minimum amplitude of the output signal is always higher than a predetermined minimum positive amplitude;
• a laser that produces a laser beam;
• and
• a modulator that modulates the laser beam with the biased and transformed output signal to provide a modulated laser beam;
• an output that directs the modulated laser beam into a proximate end of an optical fiber;
• a second node of the communication system, including:
• an optical detector for converting the modulated laser beam into a high frequency electronic input signal having high frequency positive and negative excursions in amplitude with respect to an average amplitude with some excursions being larger than other excursions;
• an input that directs the modulated laser beam from the optical fiber to the optical detector;
• a post-processor that reforms the high frequency electronic input signal to approximately duplicate the output signal.

A method of communication, comprising:

• providing an electronic output signal having high frequency positive and negative excursions in amplitude with respect to an average amplitude with some excursions being larger than other excursions;
• pre-shaping the output signal, including reducing the amplitude of larger negative excursions with respect to the excursions in the output signal, to provide a transformed output signal that includes a transformed portion of the larger negative excursions that facilitates a reconstruction of the larger negative excursions at a receiving system, so as to increase a modulation index;
• biasing the transformed output signal to provide a biased transformed output signal, so that a minimum amplitude of the biased transformed output is always higher than a predetermined minimum positive amplitude;
• producing an output laser beam;
• modulating the output laser beam with the biased transformed output signal to form a modulated output laser beam;
• and
• directing the modulated output laser beam into a proximate end of an optical fiber;
• and
• transmitting the modulated output laser beam through the optical fiber.

A method of preprocessing a signal to form a preprocessed signal for subsequent transmission, the method comprising:

• comparing the signal relative to a limit value, to identify a large excursion of the signal,
• modifying the signal to form the preprocessed signal when the large excursion is identified, and
• copying the signal to form the preprocessed signal when the large excursion is not identified;
• wherein
• modifying the signal increases a modulation index associated with the subsequent transmission.