Digital pre-distortion for mitigating modulation nonlinearity in dually modulated EML optical SSB transmitters

Dual modulation of an electro-absorption modulation laser (D-EML) is a compact and monolithically integrable optical single sideband (SSB) transmitter scheme. However, the quality of the output signal generated by the D-EML scheme could be degraded by the nonlinear distortions resulting from the cascade modulation of the directly modulated laser (DML) and electro-absorption modulator (EAM). In this Letter, we propose an effective approach to mitigate the modulation nonlinearity with the digital pre-distortion (DPD) technique to improve the signal quality and enhance the tolerance against fiber chromatic dispersion for the optical SSB signal generated by the D-EML transmitter. Significant improvement in signal-to-noise ratio and bit error rate performance at various transmission distances has been demonstrated with a 56-Gb/s optical SSB transmission system. The experimental results also show that the proposed scheme achieves power budget enhancements of ∼1.1 dB and ∼2.3 dB compared with the conventional SSB signals with and without the offset filtering scheme.