C-band real-time 400/300 Gb/s OOK bidirectional
interconnection over 20 km multicore fibers
Zhenhua Feng (冯振华)
1
, Honglin Ji (计红林)
2
, Ming Tang (唐 明)
1,
*, Lilin Yi (义理林)
2
,
Lin Gan (甘 霖)
1
,LeiXue(薛 雷)
2
, Qiong Wu (吴 琼)
1
, Borui Li (李博睿)
1
,
Jiajia Zhao (赵佳佳)
1
, Weijun Tong (童维军)
3
, Songnian Fu (付松年)
1
,
Deming Liu (刘德明)
1
, and Weisheng Hu (胡卫生)
2
1
Wuhan National Lab for Optoelectronics (WNLO) & National Engineering Laboratory for Next Generation Internet
Access System, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan,
430074, China
2
State Key Laboratory of Advanced Optical Communication Systems and Network, Shanghai Jiao Tong University,
Shanghai, 200240, China
3
State Key Laboratory of Optical fiber and Cable Manufacture Technology, Yangtze Optical fiber and Cable Joint Stock
Limited Company (YOFC), Wuhan, 430073, China
*Corresponding author: tangming@mail.hust.edu.cn
Received February 26, 2017; accepted April 21, 2017; posted online May 12, 2017
We experimentally demonstrate a real-time quasi-full-duplex 400G/300G optical interconnection over 20 km
multicore fibers (MCFs), using 10G-class transponders operated in the C-band. Optical delay interferometer
(ODI)-based optical frequency equalization is applied to mitigate chirp and dispersion induced impairments,
so that the tolerance to inter-symbol interference (ISI) can be enhanced, thus enabling 4 × 25 Gb ∕s on-off keying
(OOK) transmission per core over severely limited bandwidth channels. Real-time bit error ratio (BER) per-
formances of the bidirectional 400 Gb/s transmission are measured without using extra digital signal processing
(DSP) or electrical equalization, which ensures low complexity and less power consumption.
OCIS codes: 060.0060, 060.4510, 060.2330.
doi: 10.3788/COL201715.080602.
With the increasing capacity demands fueled by the
emerging heterogeneous and bandwidth-intensive applica-
tions, such as cloud computing, 4K/8K videos, and virtual
reality (VR), the need for low-cost, power-efficient, and
high-density short-reach optical interconnects operating
at 100 Gb/s and beyond has drawn significant research
efforts. Although advanced modulation formats
[1,2]
, includ-
ing multi-level pulse-amplitude modulation (PAM) and dis-
crete multi-tone (DMT), have been frequently proposed,
the simplest on-off keying (OOK) with intensity-modula-
tion and direct-detection (IM/DD) seems to be overlooked.
It has been shown that OOK can cost-effectively offer
good transmission performance in short-reach (∼1km)
100G optical interconnects
[3]
without using expensive dig-
ital-to-analog converters (DACs), analog-to-digital con-
verters (ADCs), or complicated digital signal processing
(DSP). However, the high baud-rate OOK signal aggra-
vates the bandwidth requirement of electrical components
and restricts the transmission distance due to dispersion.
In order to extend the transmission reach, multi-lanes
of lower-baud-rate parallel tributaries can be exploited
by stacking multiple wavelength channels into one optical
fiber through the coarse wavelength division multiplexing
(WDM)
[4,5]
.
On the other hand, as bidirectional transmission is
ubiquitous in tremendously high-density fiber cable con-
nections between servers and racks in data centers, a space
congestion problem may happen. Therefo re, reducing the
physical footprint of the optical interconnects is especially
important. Traditionally, separate optical fibers are used
as full-duplex channels in a bidirectional transmission.
Tempted by the advantages of high-density spatial chan-
nel count, integration compatibility, and lowcost, space
division multiplexing (SDM) technologies based on novel
fibers
[6–8]
have been exploited to enhance the fiber capacity
in short-range optical communication systems with
IM/DD. Few mode fibers (FMFs) can accommodate sev-
eral spatial channels using orthogonal mode division mul-
tiplexing (MDM) to support large capacity transmission
with the help of computationally intensive multiple input
multiple output (MIMO) DSP to equalize the modal
crosstalk
[9]
, otherwise, specially designed and fabricated
low-crosstalk FMF is required
[7,8]
. Besides, the attainable
spatial channel counts and the corresponding mode multi-
plexer/demultiplexer with low crosstalk and insertion
loss may be another obstacle before its deployment in
cost-sensitive optical interconnection scenarios. Instead,
the multicore fiber (MCF) is considered to be a better
choice that is suitable for high-speed optical interconnec-
tions, owing to its well-controlled inter-core crosstalk and
almost identical transmission quality compared with
standard single mode fibers (SSMFs). A six-channel par-
allel MCF interconnection using 850 nm multimode ver-
tical cavity surface emitting lasers is demonstrated with
an aggregate capacity of 120 Gb/s
[10]
. An 800 Gb/s per fi-
ber O-band transmission is also reported based on a
COL 15(8), 080602(2017) CHINESE OPTICS LETTERS August 10, 2017
1671-7694/2017/080602(5) 080602-1 © 2017 Chinese Optics Letters