Patent ID: 7756421

Claim:
A method of compensating optical signal distortions due to nonlinear and cross channel effects of an optical communications system, the method comprising steps of: determining a compensation operator C[(E(t)] that is the inverse of a link complex non-linear operator T[E(t)] representing one or more signal distortions due to nonlinear and cross channel effects imparted to a Wavelength Division Multiplexed communications signal E(t) as it traverses the optical communications system; digitally processing an electrical input signal X(t) comprising at least two parallel channel input signals x(t,ω i ) using the compensation operator C[(E(t)] to generate a predistorted electrical signal X 1 (t) comprising a respective predistorted channel input signal x 1 (t,ω i ) corresponding to each channel input signal x(t,ωi); and modulating an optical source using the predistorted channel input signals x 1 (t,ω i ) to generate corresponding predistorted optical channel signals E(t,ωi) for transmission through the optical communications system; wherein the step of digitally processing the electrical input signal X(t) comprises steps of: calculating successive numerical values of the predistorted electrical signal, X 1 (t), based on the electrical input signal X(t) and the compensation operator C[E(t)]; and converting each successive numerical value into corresponding analog values of each predistorted channel input signal x 1 (t,ω i ) of the predistorted electrical signal X 1 (t); wherein each channel input signal x(t,ω i ) of the electrical input signal X(t) comprises a substantially undistorted binary signal, and wherein the step of calculating successive numerical values of the predistorted electrical signal X 1 (t) comprises steps of: calculating a respective numerical value of the predistorted electrical signal X 1 (t) corresponding to each one of a set of predetermined N-bit sequences; storing each calculated numerical value in a look-up table; and extracting a plurality of successive numerical values of the predistorted electrical signal X 1 (t) from the look-up table using the electrical input signal X(t).