Optimization of PAM-4 transmitters based on lumped silicon photonic MZMs for high-speed short-reach optical links. - Zhou S; Wu HT; Sadeghipour K; Scarcella C; Eason C; Rensing M; Power MJ; Antony C; O'Brien P; Townsend PD; Ossieur P (Optics express, 2017)