Abstract

Four level pulse amplitude modulation (PAM-4) has become the modulation format of choice to replace on–off keying (OOK) for the 400 Gb/s short reach optical communications systems. In this paper, we investigate the possible modifications to conventional Mach–Zehnder modulator structures to improve the system performance. We present three different silicon photonic Mach–Zehnder modulator architectures for generating PAM-4 in the optical domain using OOK electrical driving signals. We investigate the transfer function and linearity of each modulator and experimentally compare their PAM-4 generation and transmission performance with and without use of digital signal processing (DSP). We achieve the highest reported PAM-4 generation and transmission without the use of DSP. The power consumption of each modulator is presented, and we experimentally show that multielectrode Mach–Zehnder modulators provide a clear advantage at higher symbol rates compared to conventional Mach–Zehnder modulators.

© 2019 CCBY

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