Silicon based Mach Zehnder modulators, unlike lithium niobate, suffer from nonlinear pattern-dependent behavior beyond simple intersymbol interference. We experimentally demonstrate a novel predistortion method based on the iterative learning control (ILC) technique to address this issue using quasi-real-time adaptation with hardware-in-the-loop. We compare bit error rate performance to that of linear solutions at several M-QAM modulation levels and baud rates. We demonstrate 256QAM at 20 Gbaud which linear compensation alone cannot achieve. For 40 Gbaud 128QAM, we improve power sensitivity by 4.4 dB. We combine optical compensation with ILC to improve power sensitivity by ∼ 5 dB for 60 Gbaud 32QAM.