A 2.4pJ/b 100Gb/s 3D-integrated PAM-4 Optical Transmitter with Segmented SiP MOSCAP Modulators and a 2-Channel 28nm CMOS Driver
Arian Hashemi Talkhooncheh, Weiwei Zhang, Minwo Wang, David J. Thomson, Martin Ebert, Ke Li, Graham T. Reed, Azita Emami
Abstract
Data centers continue to require interconnects with higher bandwidth densities and energy efficiencies. Silicon photonics (SiP)-based solutions have gained interest for implementing low-cost and power efficient 100+Gb/s/A optical transceivers. While microring modulators (MRMs) have small footprints and high electro-optical bandwidth (EOBW), they suffer from an inherent tradeoff between bandwidth and optical phase efficiency, high sensitivity to process and temperature variations, and non-linear electro-optic characteristics [1 – 2]. Travelling-wave Mach-Zehnder Modulators (TW-MZMs) require power-hungry drivers to compensate microwave losses and occupy large areas on chip [3 – 4]. Metal-oxide-silicon-capacitor (MOSCAP)-based phase modulators can significantly scale the area and power of the optical transmitter (OTX) owing to their superior optical efficiency (voltage-length product at n phase shift of V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</inf> L < 1Vmm) and compact footprint (< 1mm) [5]. MOSCAP modulators, however, impose large capacitive parasitics (~3fF/μm), which could limit the electro-optical bandwidth (EOBW) significantly. State-of-the-art wireline transmitters cannot meet the requirements of MOSCAP modulators due to their 50Ω-terminated design and limited output voltage swing [6]. This paper presents a 3D-integrated 100Gb/s PAM-4 OTX with electronic pre-distortion (PD) and BW extension techniques to compensate for MOSCAP modulator BW limitations.