Digital Pre-Distortion for Mach-Zehnder Modulators in IMDD Optical Systems

We present a digital pre-distortion (DPD) scheme to compensate for Mach-Zehnder modulator (MZM) in intensity modulation and direct detection (IMDD) optical systems. In our DPD scheme, the modulator driving signal is pre-distorted to mitigate the distortion introduced by the nonlinear transfer function of the MZM. The DPD scheme is performed in two steps: first, the coefficient of the nonlinear impairment is computed using the predefined mathematical models of the optical back-to-back (BTB) IMDD system; second, an adjusting factor of the DPD is introduced and optimized to obtain the best performance of the system. Both numerical simulations and experimental demonstrations were conducted to assess the DPD gain for feed-forward equalization (FFE) and third-order Volterra filter equalization (VFE), respectively. In experimental C-band 20 GBaud four-level pulse amplitude modulation (PAM4) IMDD optical BTB system. DPD scheme can obtain 2.4 dB and 1.2 dB improvement of receiver sensitivity for FFE and VFE at a bit error ratio (BER) for 1 × 10-3, respectively.