Abstract: A system for correcting nonlinear distortion in fiber optic systems including communication systems by means of light modulation provided by interferometric modulators such as the Mach-Zehnder. The present invention involves the addition of a correction signal which contains error canceling information. The additive correction signal optical beam is frequency shifted or phase scrambled through the use of a phase or frequency modulator. This insures the corrective light signal adds incoherently or quasi-incoherently within the signal bandwidth of interest. Furthermore, the present system requires only a single light source and can be made independent of wavelength and is easily optimized with active servo devices. A system provided by the present invention also provides improvement over the state of the art because of its high degree of correction and independence from link length using ordinary single mode fibers.