A Silicon Photonic PAM-4 Modulator Based on Dual-Parallel Mach–Zehnder Interferometers

We present a silicon photonic dual-parallel Mach-Zehnder modulator (MZM) operating near 1550 nm used for four-level pulse amplitude modulation (PAM-4). The differential and integral nonlinearities of the device are investigated. A driving scheme and a biasing method that improves the linearity and PAM operation of the device are presented. The measured second harmonic distortion and two-tone, third-order intermodulation spurious-free dynamic range are 75 dB · Hz
^1/2
and 86 dB · Hz
^3/2
, respectively. We further investigate the performance of the device in a short-reach transmission system. We report a successful 50-Gbaud single-wavelength transmission of PAM-4 over 2 km of single-mode fiber (SMF) below hard decision pre forward error correction (pre-FEC) threshold of 4.4 × 10
^-3
.