Generation of O-band PAM-4 signal using a silicon modulator driven by two binary sequences

Abstract

Silicon photonics is a promising solution for next generation of short-range optical communication systems. Silicon modulators have driven an important research activity over the past years, and many transmission links using on-off keying modulation format (OOK) were successfully demonstrated with a large diversity of modulator structures. In order to keep up with the demand of increasing bitrates for limited bandwidths in Datacom applications, higher modulation formats are explored, such as quadrature phase shift keying (QPSK) or 4-level pulse amplitude modulation (PAM-4). However, driving the modulators to generate PAM-4 signals commonly require expensive and power-hungry electronic devices such as digital-to-analog converters (DACs) for pulse-shaping and digital signal processors (DSP) for nonlinearity compensation. Lastly, new solutions were studied to overcome this issue, including new driving methods based on the use of two different input binary sequences applied directly on the modulator. While most of the reported works are focused on the C-band of communication, the O-band can present a definitive advantage due to the low dispersion of standard single-mode (SSMF) fiber. For those reasons, we demonstrate the generation of a 10-Gbaud DAC-less PAM-4 signal in the O-band using a depletion-based silicon traveling wave Mach-Zehnder modulator (TWMZM). An open eye diagram was obtained, and a bit error rate (BER) of 3.8×10-3 was measured for a received optical power of about -6 dBm.