Laser nonlinearity compensation for subcarrier multiplexed optical transmission systems.

Abstract

Subcarrier multiplexing efficiently uses the available fiber bandwidth in video transmission. Semiconductor lasers are usually used as optical transmitters in such systems. A semiconductor laser exhibits nonlinear characteristics. Nonlinearity degrades system performance. For nonlinearity compensation, a nonlinear predistortion block is assumed to be incorporated prior to the laser. Characteristics of this nonlinear block invert those of the laser. Performance of the subcarrier multiplexed system with and without predistortion is evaluated by harmonic distortion and intermodulation distortion analyses. Nonlinear distortion level decreases significantly when predistortion is employed prior to the laser. This enhancement results in system requirements for carrier-to-noise ratio being met.