Abstract

Optical transmitters for four-level pulse amplitude modulation (PAM-4) have attracted a significant amount of research in recent years, in large part due to the standardization of the format for the 200 and 400 Gigabit Ethernet optical interconnects in data centers. However, combining low-power and linear operation of the electro-optical frontend with sufficiently large bandwidths has proven challenging, especially for the 100 Gb/s/λ links (i.e., employing 50 Gbaud PAM-4). The most straightforward solution has been to deal with the non-idealities of the modulator in the electrical domain: predistorting the signal levels and/or equalizing the frequency response with the help of digital signal processing (DSP). However, this typically requires fast digital-to-analog converters (DACs), either capable of delivering large swings (> 1 Vpp) or supplemented with an additional linear amplifier to drive the optical modulator. Both options substantially increase the power consumption and the complexity of the transceiver. Rather than allocating effort to linearize the electrical to optical conversion of a single modulator, we propose a topology that performs the DAC operation in the optical domain. Two compact electro-absorption modulators in an interferometer layout are driven with NRZ data to generate the four-level signal in the optical domain. Using this topology, we demonstrate the first real-time 128 Gb/s PAM-4 transmission with a silicon photonic transmitter in a chip-to-chip link. In a back-to-back setup, we obtained a bit-error ratio (BER) of 4 × 10⁻¹⁰ without requiring any DAC, DSP, or modulators with large traveling wave structures. Over 1 km of standard single mode fiber a BER of 8 × 10⁻⁶ is recorded, still well below the KP4 forward error-coding limit. These results correspond to the lowest BERs reported for any real-time PAM-4 link at 100 Gb/s or higher, illustrating the benefit of performing the DAC operation in the optical domain.

© 2018 IEEE

Experimental parametric study of 128 Gb/s PAM-4 transmission system using a multi-electrode silicon photonic Mach Zehnder modulator

Alireza Samani, David Patel, Mathieu Chagnon, Eslam El-Fiky, Rui Li, Maxime Jacques, Nicolás Abadía, Venkat Veerasubramanian, and David V. Plant
Opt. Express 25(12) 13252-13262 (2017)

Silicon photonic dual-drive MIM based 56 Gb/s DAC-less and DSP-free PAM-4 transmission

Rui Li, David Patel, Eslam El-Fiky, Alireza Samani, Zhenping Xing, Yun Wang, and David V. Plant
Opt. Express 26(5) 5395-5407 (2018)

400 Gb/s O-band silicon photonic transmitter for intra-datacenter optical interconnects

Eslam El-Fiky, Alireza Samani, David Patel, Maxime Jacques, Mohamed Sowailem, and David V. Plant
Opt. Express 27(7) 10258-10268 (2019)

Monolithic 56 Gb/s silicon photonic pulse-amplitude modulation transmitter

Chi Xiong, Douglas M. Gill, Jonathan E. Proesel, Jason S. Orcutt, Wilfried Haensch, and William M. J. Green
Optica 3(10) 1060-1065 (2016)

50 GBd PAM4 transmitter with a 55nm SiGe BiCMOS driver and silicon photonic segmented MZM

Laurens Breyne, Hannes Ramon, Kasper Van Gasse, Michiel Verplaetse, Joris Lambrecht, Michael Vanhoecke, Joris Van Campenhout, Günther Roelkens, Peter Ossieur, Xin Yin, and Johan Bauwelinck
Opt. Express 28(16) 23950-23960 (2020)