Bias-drift-free Mach–Zehnder modulators based
on a heterogeneous silicon and lithium niobate
platform
SHIHAO SUN,
1
MINGBO HE,
1
MENGYUE XU,
1
SHENGQIAN GAO,
1
ZIYAN CHEN,
1
XIAN ZHANG,
2
ZILIANG RUAN,
2
XIONG WU,
3
LIDAN ZHOU,
1
LIN LIU,
1
CHAO LU,
3
CHANGJIAN GUO,
2
LIU LIU,
4
SIYUAN YU,
1
AND XINLUN CAI
1,
*
1
State Key Laboratory of Optoelectronic Materials and Technologies and School of Electronics and Information Technology, Sun Yat-sen
University, Guangzhou 510000, China
2
Centre for Optical and Electromagnetic Research, Guangdong Provincial Key Laboratory of Optical Information Materials and Technology, South
China Academy of Advanced Optoelectronics, South China Normal University, Higher-Education Mega-Center, Guangzhou, China
3
Department of Electronic and Information Engineering, Photonics Research Centre, The Hong Kong Polytechnic University, Hung Hom, Kowloon,
Hong Kong, China
4
State Key Laboratory for Modern Optical Instrumentation, Centre for Optical and Electromagnetic Research, Zhejiang Provincial Key Laboratory
for Sensing Technologies, Zijingang Campus, Zhejiang University, Hangzhou 310058, China
*Corresponding author: Caixlun5@mail.sysu.edu.cn
Received 20 July 2020; revised 28 September 2020; accepted 22 October 2020; posted 23 October 2020 (Doc. ID 403167);
published 30 November 2020
Optical modulators have been and will continue to be essential devices for energy- and cost-efficient optical com-
munication networks. Heterogeneous silicon and lithium niobate modulators have demonstrated promising per-
formances of low optical loss, low drive voltage, and large modulation bandwidth. However, DC bias drift is a
major drawback of optical modulators using lithium niobate as the active electro-optic material. Here, we dem-
onstrate high-speed and bias-drift-free Mach–Zehnder modulators based on the heterogeneous silicon and lith-
ium niobate platform. The devices combine stable thermo-optic DC biases in silicon and ultra-fast electro-optic
modulation in lithium niobate, and exhibit a low insertion loss of 1.8 dB, a low half-wave voltage of 3 V, an
electro-optic modulation bandwidth of at least 70 GHz, and modulation data rates up to 128 Gb/s.
© 2020
Chinese Laser Press
https://doi.org/10.1364/PRJ.403167
1. INTRODUCTION
By harnessing the tool sets and process flows in complementary
metal–oxide–semiconductor (CMOS) foundries based on
silicon-on-insulator (SOI) platforms, silicon photonics (SiPh)
promises advantages of low cost, high volume, and reliable
manufacturing [1–3] and therefore may create a radically new
landscape for photonic integrated circuits (PICs). This makes it
very attractive for applications in future transceivers in telecom-
munication and data communication [4], in which fast, energy-
efficient, and low-loss electro-optical (EO) modulators are
crucial components [5,6]. As an essential component, optical
modulators on SiPh platforms commonly use the plasma
dispersion effect in silicon p−n junctions [7–10]. With this
technology, various impressive devices have been developed,
leading to commercial 100 Gb/s optical transceivers for the
telecom and datacom applications [11]. However, the plasma
dispersion effect has intrinsic limitations in modulation band-
width and optical loss. In particular, because of free carrier
absorption, silicon p− n junctions do not support pure phase
modulation, which deteriorates the fidelity of signals in ad-
vanced modulation format s. The current performance envelope
of the silicon optical modulator is believed to be more or less
close to their physical limits, but future applications require
even higher performance due to the insatiable demands of data
capacity.
To overcome the drawbacks inherent in silicon modulators,
a diverse range of materials offering better modulation perfor-
mance have been heterogeneously co-integrated onto the SiPh
platform, including graphene [12], EO polymers [13], indium
phosphide (InP) [14], and barium titanate (BTO) [15]. Besides
these materials, lithium niobate (LN), the most successful
material for high-speed optical modulation [16–22], has also
been integrated with SOI circuits by the die-to-wafer bonding
technique [23–26]. Recently, we have demonstrated a hetero-
geneous LN/SOI Mach–Zehnder modulator (MZM) [27],
which exhibits low insertion loss <2 .5dB, large bandwidth
1958
Vol. 8, No. 12 / December 2020 / Photonics Research
Research Article
2327-9125/20/121958-06 Journal © 2020 Chinese Laser Press