In this paper, we present a field-trial C-band 72Gbit/s optical on-off keying (OOK) system over 18.8 km dispersion-uncompensated submarine cable in the South China Sea. Chromatic dispersion (CD) of causes four spectral nulls on 36 GHz bandwidth OOK signal, which is main obstacle for achieving an acceptable bit-error-rate (BER) performance. Decision feedback equalizer (DFE) effective to compensa...