Optical transmitters linearized by means of parametric feedback

An optical transmission or distribution system for broadband signals comprising:

• an optical transmitter for providing transmitted optical power comprising:
• a light source;
• an electrical-to-light modulation means for modulating said light having a first non-linear modulation transfer characteristic having an associated shape, there being a bias point on said characteristic, said modulation means including an information signal input for receiving an electrical modulation signal, an output for providing a modulated signal, and means for adjusting said modulation means;
• one or more optical receivers;
• a fiber optic distribution network for receiving said modulated light and distributing said modulated light to said optical receivers;
• and
• a parametric feedback system comprising:
• means coupled to said modulation means to superpose one or more pilot signals upon said electrical modulation signal;
• preconditioning means coupled to said modulation means for providing electronic pre-conditioning of said electrical modulation signal, comprising:
• means for providing non-linear predistortion to said modulation signal, having a second non-linear transfer characteristic;
• and
• means to adjust said second non-linear transfer characteristic of said pre-conditioning means;
• a monitoring optical receiver;
• means to route a portion of modulated light to said monitoring optical receiver;
• means coupled to said monitoring optical receiver to generate error signals indicative of the deviations of the system away from optimum points of minimal harmonic distortion and intermodulation associated with said system, by monitoring the amounts of distortion generated by interaction of said pilot signals with the overall nonlinearity of said optical transmitter;
• means to electronically process said error signals to provide processed error signals;
• and
• means to feed back said processed error signals to said means for providing electronic pre-conditioning in order to adjust the overall transfer characteristic of said means for providing electronic pre-conditioning and said modulation means such that the harmonic distortion and intermodulation components in the spectrum of the modulated signal at the output of said optical transmitter are reduced.