Abstract: In an amplified wavelength division multiplexes (WDM) fiber optic communication system, each channel experiences a different optical gain, dispersion and noise. Also, the evolution of WDM fiber optic systems to higher density channel spacing has further aggravated multi-channel non-linear distortions such as four-wave mixing (FWM) and cross-phase modulation (XPM). The standard method for controlling these nonlinearities is the peak power control method. The performance of the channels can be equalized by adjusting the transmission powers of the optical transmitters. However, just equalization of a performance indication factor (PIF) such as BER or Q is not the optimum approach when peak power control mode of operation dominates. This invention is directed towards improving the margins of performance of WDM fiber optic channels.

Abstract: Apparatus for providing a reference pseudo-noise ("PN") sequence, and for providing a secondary PN sequence shifted with respect to the reference PN sequence by a number of chips that can be sequentially shifted. The apparatus includes a first pseudo-noise sequence generator ("PNSG"), the PNSG generating the reference PN code, having N stages, each stage being at one of two states, and having a feedback loop from the output of the PNSG, the value on the feedback loop being stored in each stage 1, 2, 3, . . . N, after being multiplied by a constant associated with the stage, C1, C2, C3, . . . CN, respectively, and the result added to the value in the previous stage, with "0" being deemed to be the value in the stage previous to the first stage, and then stored in the stage. Also provided is a mask generator/shifter comprising a second PNSG having N stages, wherein the N stages of the second PNSG may be loaded with a shift-and-add mask, M=m.sub.1, m.sub.2, . . . m.sub.N-1, m.sub.N.