Nonlinear distortion suppression in directly modulated DFB-LD by dual-parallel modulation

A novel method to suppress nonlinear distortion of directly modulated laser diodes using a dual parallel modulation scheme has been proposed. The scheme exploits the fact that frequency chirping influences the phase of RF signals. Two properly controlled undesired intermodulation signals with out-of-phase difference are cancelled via coherent RF recombination at the photodetector. The validity of this scheme was confirmed through experiments. A 20-dB reduction of the third-order intermodulation distortion was achieved and tunability of the suppression region was observed.