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An intersymbol interference (ISI)-suppressed optical multilevel modulation technique that is applicable to a wide range of binary and multilevel signaling is proposed. It employs binary phase-shift keying modulations that are generated by Mach-Zehnder intensity modulators as basic building blocks, and complex multilevel modulations are synthesized using interferometric addition and tandem modulations. Its feasibility and ISI suppression effect are verified in various binary and multilevel signal synthesis schemes using numerical simulations. Furthermore, the generation of ISI-suppressed zero-chirp binary and quaternary amplitude-shift keying modulations is experimentally demonstrated. Finally, its applicability to complex optical multilevel signaling is shown in the generation of a 40-Gb/s 16-level amplitude- and phase-shift keying signal, which results in 3-dB sensitivity improvement compared with the one using a conventional four-level electrical driving signal.