System and method for minimizing nonlinear distortion in optical communication systems employing laser intensity modulation

摘要

An amplitude limiting circuit (20) is utilized to select the most favorable linear region of the light vs. current characteristic curve (for directly modulated lasers (22)) or the laser's modulator transfer function (for externally modulated lasers) by preventing excursions of the broadband, multiplexed input signal (I_m (t)) beyond selected upper and lower current or voltage limits. The clipped broadband signal (I_c (t)) is represented as a stationary Gaussian process to provide a reliable estimate of the carrier-to-nonlinear distortion per channel that would be experienced with a given laser or optical modulator.;The distortion control technique of the present invention is equally applicable for both directly and externally modulated lasers. In a directly modulated system, for example, an amplitude limiter (20) may be used to clip the multiplexed signal to prevent excursions below the threshold and/or above saturation and thereby avoid the unpredictable levels of nonlinear distortion associated therewith. Instead, the clipping levels can be set to achieve an acceptably low level of non-linear distortion.