220nm Si层上的高速Ge电吸收调制器实现
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"这篇论文介绍了一种56 Gbps高速锗电吸收调制器（Ge electro-absorption modulator，EAM），它基于硅基绝缘体上硅（silicon-on-insulator, SOI）平台，采用220纳米顶层硅结构。这种调制器通过选择性生长的三角形锗材料直接构建其锗波导部分，设计了一个不对称的p-i-n结以增强 Franz-Keldysh 效应，从而实现高效调制。在1610纳米波长下，该Ge EAM的插入损耗为6.2分贝，展示了高性能的电光特性。"
详细说明:
该研究重点在于开发一种高速、高效且工艺简单的锗电吸收调制器，用于光通信系统。电吸收调制器是光电子集成中的关键组件，它们能够通过改变光在材料中的吸收率来调制光信号，从而实现数据传输。在这个项目中，研究人员采用了一个特殊的结构设计，即蒸发耦合的锗波导电吸收调制器，其优点在于简化了制造流程。
在材料选择上，他们使用了220纳米厚的顶层硅的SOI平台，这种平台在光电子学领域广泛使用，因为它提供了良好的光子和电子性能。此外，他们创新地选择了选择性生长的三角形锗材料来构建调制器的波导部分。这种几何形状的选择有助于提高光与材料的相互作用效率，从而优化调制性能。
在设计上，他们引入了一个不对称的p-i-n结。在锗波导内部设置这样的结，可以有效地在材料中产生强烈的电场，这是利用Franz-Keldysh效应的关键。Franz-Keldysh效应是指在半导体中强电场的作用下，能带结构的弯曲导致吸收边的移动，从而改变光吸收特性。这种效应使得调制器能够在较小的电压下实现高效的光调制。
论文中提到，在1610纳米的波长下，Ge EAM的插入损耗仅为6.2分贝，这表明了该器件具有低损耗的特点，这对于长距离、高数据速率的通信至关重要。同时，该调制器展示了高速性能，能够达到56 Gbps的数据速率，这意味着它有潜力应用于未来超高速光通信网络。
这篇研究工作成功地开发出一种基于锗材料的高速电吸收调制器，它的简单制造工艺、低损耗特性和高速性能使其成为光电子集成领域的有前景的技术，对于推动下一代光通信技术的发展具有重要意义。
56 Gbps high-speed Ge electro-absorption
modulator
ZHI LIU,
1,2
XIULI LI,
1,2
CHAOQUN NIU,
1,2
JUN ZHENG,
1,2
CHUNLAI XUE,
1,2
YUHUA ZUO,
1,2
AND
BUWEN CHENG
1,2,3,
*
1
State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
2
Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
3
Beijing Academy of Quantum Information Sciences, Beijing 100193, China
*Corresponding author: cbw@semi.ac.cn
Received 25 June 2020; revised 5 August 2020; accepted 19 August 2020; posted 20 August 2020 (Doc. ID 401140); published 29 September 2020
A high-speed evanescent-coupled Ge waveguide electro-absorption modulator (EAM) with simple fabrication
processes was realized on a silicon-on-insulator platform with a 220 nm top Si layer. Selectively grown Ge with
a triangle shape was direc tly used for Ge waveguides of the EAM. An asymmetric p-i-n junction was designed in
the Ge waveguide to provide a strong electric field for Franz–Keldysh effect. The insertion loss of the Ge EAM was
6.2 dB at 1610 nm. The EAM showed the high electro-optic bandwidth of 36 GHz at −1V. Clear open 56 Gbps
eye diagrams were observed at 1610 nm with a dynamic extinction ratio of 2.7 dB and dynamic power consump-
tion of 45 fJ/bit for voltage swing of 3V
pp
. © 2020 Chinese Laser Press
https://doi.org/10.1364/PRJ.401140
1. INTRODUCTION
Future optical interconnect systems needed high-speed, low-
power, and low-cost optical components to meet the demands
of rapidly growing data communication. Si-based photonics
was a promising technology for this application [1], as it is
highly compatible with Si complementary metal–oxide–semi-
conductor (CMOS) technology. Basic devices of the Si photon-
ics such as high-speed photodetectors [2–4], modulators [5–8],
and many passive components [9] have been widely studied.
Among these devices, the modulator was the key device that
largely determines the quality of the transmitting signal in op-
tical links. Due to the weak electro-optical effect, most high-
speed Si modulators were demonstrated by using free carrier
dispersion effects in the phase-shift structure. Si modulators
with a Mach–Zehnder interferometer could realize high-speed
modulation, broad optical bandwidth, and robust thermal tol-
erance [7]. But, they suffered from large footprints on the order
of mm
2
, which incur relatively high power consumption. The
footprint and power consumption of the Si modulators could
be reduced dramatically by using ring or photonic crystal con-
figuration [5]. However, this improvement was obtained on the
sacrifice of optical bandwidth, thermal tolerance, and fabrica-
tion tolerance [8]. To balance these parameters, Ge or GeSi
electro-absorption modulators (EAMs) based on the Franz–
Keldysh (FK) effect have emerged [10–15]. Recently, 56 Gbps
high-speed Ge and GeSi EAMs with lateral p-i-n or wrap-
around p-i-n structure were demonstrated [13,14]. Some of
these EAMs even had the capability of transmitting single-lane
100 Gbps [15]. However, the fabrication processes of these
EAMs were very complex. Some EAMs required chemical–
mechanical polish (CMP) of Ge and extra poly-Si tapers
[13,15], and other EAMs needed several precise Ge etchings
[11,12,14].
In this paper, we presented a novel evanescently-coupled
high-speed Ge waveguide EAM on 220-nm-thick silicon-on-
insulator (SOI) platform. The fabrication processes of the
EAM were simple. The Ge waveguide with two Ge tapers
of the EAM was selectively grown on a Si waveguide.
Neither CMP nor Ge etching was necessary. An asymmetric
p-i-n junction was employed to change the electric field inten-
sity of the Ge layer for the FK effect. The static characteristics
including dark current, optical responsivity, insertion loss (I L),
dc extinction ratio (ER), and power consumption were studied.
The electro-optic 3 dB bandwidth, modulated bit rate, and
dynamic power consumption exhibited the high-speed perfor-
mance of the Ge EAM.
2. DESIGN AND FABRICATION
Figure 1(a) shows a schematic view of our EAM. The light
came from the input Si waveguide and evanescently coupled
into/out of the EAM through three-dimensional Ge tapers.
A similar structure was demonstrated for a high-responsivity
Ge photodetector [16]. The cross-sectional shapes of the Ge
tapers and waveguide were isosceles triangles. The shape of
the Ge depended on growth conditions. Moderate growth tem-
perature and low growth pressure would lead the triangle with a
1648
Vol. 8, No. 10 / October 2020 / Photonics Research
Research Article
2327-9125/20/101648-05 Journal © 2020 Chinese Laser Press
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