Nonlinear digital pre-distortion of transmitter components

We present a linear and nonlinear digital predistortion (DPD) tailored to the components of an optical transmitter. The DPD concept uses nonlinear models of the transmitter devices, which are obtained from direct component measurements. While the digital-to-analog converter and driver amplifier are modeled jointly by a Volterra series, the modulator is modeled independently as a Wiener system. This allows for block-wise compensation of the modulator by a Hammerstein system and a pre-distortion of the electrical components by a second Volterra series. In simulations and extensive experiments, the performance of our approach for nonlinear DPD is compared to an equivalent linear solution as well as to a configuration without any digital pre-distortion. The experiments were performed using M-ary quadrature-amplitude modulation (MQAM) formats ranging from 16-QAM to 128-QAM at a symbol rate of 32 GBd. It is shown that DPD improves the required optical signal-to-noise ratio at a bit error ratio of 2???10-2 by at least 1.2 dB. Nonlinear DPD outperforms linear DPD by an additional 0.9 dB and 2.7 dB for higher-order modulation formats such as 64-QAM and 128-QAM, respectively.