Electrical domain compensation of non-linear effects in an optical communications system

A compensation system for compensating optical signal distortions due to nonlinear and cross channel effects of an optical communications system, the compensation system comprising:

• a processor for 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 non-linear and cross channel effects imparted to a Wavelength Division Multiplexed communications signal E(t) as it traverses the optical communications system;
• a compensation processor for digitally processing an electrical input signal X(t) comprising at least two parallel channel input signals x(t,ωi) using the compensation operator C[(E(t)] to generate a predistorted electrical signal X1(t) comprising a respective predistorted channel input signal x1(t,ωi) corresponding to each channel input signal x(t,ωi);
• and
• an optical modulator for modulating an optical source using the predistorted channel input signals x1(t,ωi) to generate a corresponding predistorted optical channel signals E(t,ωi) for transmission through the optical communications system;
• wherein the compensation processor comprises:
• a digital filter for filtering the electrical input signal X(t) using the compensation operator C[E(t)] to generate a series of successive numerical values of the predistorted electrical signal X1(t);
• and
• a digital-to-analog converter for converting each successive numerical value into corresponding analog values of each predistorted channel input signal x1(t,ωi) of the predistorted electrical signal X1(t);
• wherein the digital filter comprises a Look-up table comprising:
• a serial to parallel converter (SPC) for converting the electrical input signal X(t) into a series of successive N-bit words;
• and
• a Random Access Memory (RAM) coupled to receive each N-bit word from the SPC, the RAM being adapted to store a plurality of numerical values of the predistorted electrical signal X1(t), and output a selected one numerical value based on the N-bit word from the SPC.

A distortion compensator for compensating optical signal distortions due to nonlinear and cross channel effects of an optical communications system, the distortion compensator comprising:

• a compensation processor for digitally processing an electrical input signal X(t) comprising at least two parallel channel input signals x(t,ωi) using a predetermined complex compensation operator C[(E(t)] to generate a predistorted electrical signal X1(t) comprising a respective predistorted channel input signal x1(t,ωi) corresponding to each channel input signal x(t,ωi), the compensation operator C[E(t)] being 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 an optical link of the optical communications system, such that modulation of an optical source using the predistorted channel input signals x1(t,ωi) generates a corresponding predistorted optical channel signals E(t,ωi) for transmission through the optical link;
• wherein the compensation processor comprises:
• a digital filter for filtering the electrical input signal X(t) using the compensation operator C[E(t)] to generate a series of successive numerical values of the predistorted electrical signal X1(t);
• and
• a digital-to-analog converter for converting each successive numerical value into corresponding analog values of each predistorted channel input signal x1(t,ωi) of the predistorted electrical signal X1(t);
• wherein the digital filter comprises a look-up table comprising:
• a serial to parallel converter (SPC) for converting the electrical input signal X(t) into a series of successive N-bit words;
• and
• a Random Access Memory (RAM) coupled to receive each N-bit word from the SPC, the RAM being adapted to store a plurality of numerical values of the predistorted electrical signal X1(t), and output a selected one numerical value based on the N-bit word from the SPC.