NEC: World's Largest Transmission Capacity with Standard Diameter Multi-Core Optical Fiber
2017年8月8日 - 6:36PM
JCN Newswire (英)
Nippon Telegraph and Telephone Corporation, and six partners,
KDDI Research, Inc., Sumitomo Electric Industries, Ltd., Fujikura
Ltd., Furukawa Electric Co., Ltd., NEC Corporation, and Chiba
Institute of Technology have demonstrated the world's largest
transmission capacity of 118.5 Tera-bit/s(1) using a multi-core
fiber with four optical paths (cores) in the same diameter of
currently used optical fiber.
A conventional glass diameter (125 micrometer)(2) in accordance
with the international standard enables us to use existing optical
fiber fabrication and optical connector technologies effectively.
This achievement proves the concept of multi-core fiber based
long-haul and large capacity transmission system consisting of
multiple vendor technologies, and it makes significant progress on
practical use of the multi-core fiber technology.
We will aim to introduce the standard diameter multi-core fiber by
the early 2020s. We will also continue to contribute the
realization of a future optical infrastructure which can support
variety of data communication demands.
This remarkable achievement was reported in 4 August as a
postdeadline paper(3) at the Opto Electronics and Communications
Conference (OECC 2017), the largest conference on optical
communication in Asia Pacific-Rim, which was held at Sands Expo and
Convention Centre, Singapore.
This work was partially based on work commissioned by the National
Institute of Information and Communications Technology (NICT).
http://www.acnnewswire.com/topimg/Low_NEC8817Fig1.jpg
Figure 1: Features of the proposed multi-core fiber
Research Background
World wide spread of various mobile terminal and data services
continuously increases the transmission capacity more than 10% per
year all over the world. This trend may cause capacity crunch in
the currently used optical fiber by the late 2020s. Moreover, the
expansion of optical fiber count and the convergence of optical
wiring particularly in the data center and/or central office, which
is caused by the world wide data capacity increase, would be
serious problem.
With these as backgrounds, a multi-core fiber having multiple
optical paths (cores) in one fiber has been investigated
intensively all over the world in order to overcome the future
capacity crunch and to realize the high density or space saving
optical facilities. For example, ultra large capacity transmission
experiments using a multi-core fiber with 10 cores or more have
been demonstrated(4). However, these high core count multi-core
fiber usually needs a thicker glass diameter, and it requires an
extreme advance in the fabrication process and further development
on sub-components. As a result, it is considered that 10 years or
so would be necessary to make the high core count multi-core fiber
practical.
In order to accelerate using the multi-core fiber technology, NTT,
KDDI Research, Sumitomo Electric, Fujikura, Furukawa, NEC, and CIT
developed a multi-core fiber with a conventional diameter in
accordance with the current International standard. It enables to
use existing optical fiber technology even though it limits the
number of cores to 4-5.
Summary of Achievements
NTT, KDDI Research, Sumitomo Electric, Fujikura, Furukawa, NEC, and
CIT:
- Clarified the design guideline for a multi-core fiber with
conventional glass diameter in accordance with International
standard,
- Realized a multi-core transmission line composed of a standard
diameter multi-core fibers fabricated by multiple vendors,
- Proved a beyond 100 Tera-bit/s transmission using the standard
diameter multi-core fiber transmission line.
These studies led to three major achievements:
- 4-5 cores can be arranged within a 125 micrometer glass diameter
while maintaining the same transmission quality with the current
optical fiber,
- A 316 km long multi-core transmission line is realized with a
0.21 dB/km average loss*5 concatenating the standard diameter
multi-core fibers (4 cores) fabricated by multiple vendors
randomly,
- World's largest transmission capacity of 118.5 Tera-bit/s is
achieved among a standard diameter optical fiber using a multi-core
transmission system composed of the above multi-core transmission
line, multi-core optical amplifiers, and the existing optical
connectors.
As a results, we successfully revealed the capacity
extensionability and affinity with the existing technology of our
multi-core fiber in accordance with the International standard of
the current optical fiber.
Detail of Achievements
1.Design Guideline
During the fabrication process of an optical fiber, a relatively
large size glass rod with a diameter of several to ten centimeters,
namely preform, is prepared. An optical fiber is realized by
melting and drawing the preform while keeping the geometrical
similarity. When a glass diameter of an optical fiber is enlarged
two times (e.g. from conventional 125 micrometer to 250
micrometer), the fabrication length obtained with the same size
preform is reduced to a quarter. Therefore, the increase in the
glass diameter directly affects the mass-productivity of an optical
fiber. The current optical communication system is commonly using a
single-mode fiber (SMF) with a core diameter of about 10 micrometer
and it which can be used in all the telecommunication wavelength
region (1260 nm - 1625 nm).
We then aim to realize a multi-core fiber with two features: i)
having a glass and coating diameter of 125+/-0.7 micrometer and
235-265 micrometer in accordance with the International standard of
the current optical fiber, ii) whose individual core can have the
similar transmission quality with the commonly used SMF. In a
multi-core fiber, the optical signal interference between
neighboring cores(6) should be reduced sufficiently. NTT and KDDI
Research revealed that 4-5 cores can be arranged in a 125
micrometer glass diameter.
http://www.acnnewswire.com/topimg/Low_NEC8817Fig2.jpg
Figure 2: Schematic image of productivity reduction caused by a
glass diameter enlargement, and example multi-core fibers with a
standard glass diameter
2. Multi-core transmission line composed of multiple vendor optical
fibers
Based on the above design guideline, Sumitomo Electric, Fujikura,
and Furukawa individually fabricated a multi-core fibers with four
cores and more than 100 km length. All multi-core fibers can be
used in the 1260 nm - 1625 nm wavelength region, and having the
similar transmission property to the current SMF (cf. Mode filed
diameter (MFD)(7) at 1550 nm is 9-10 micrometer).
The fabricated multi-core fibers were divided into a 20-40 km long
pieces, and three transmission spans with a length of 104-107 km
were re-constructed by splicing the multi-core fibers provided by
different vendors intentionally. A satisfactory low loss features
which is comparable to the conventional SMF was achieved. An
average loss of four cores in each span was 0.22 dB/km or less
including splicing losses. We spliced two multi-core fibers by
melting each end, namely fusion splice technology. A 0.21 dB/km
loss property was achieved as the average of all three spans.
These achievements indicate that our standard diameter multi-core
fiber with similar transmission quality (MFD) with the conventional
SMF enables us to greatly improve the productivity of the
multi-core fiber made by the effective use of the existing
fabrication technology and knowledge.
http://www.acnnewswire.com/topimg/Low_NEC8817Fig3.jpg
Figure 3: Schematic image of multi-core transmission line composed
of different vendors and its loss characteristics
3. Beyond 100 Tera-bit transmission
A multi-core transmission system was constructed by concatenating
three spans. Three multi-core optical amplifiers fabricated by NEC,
KDDI Research, NTT, and Furukawa were inserted at each end of three
spans in order to compensate the signal attenuation. Cladding
pumping type multi-core optical amplifiers which is expected to
reduce power consumption were used, and a 16% improvement was
confirmed in this achievement(8). In order to confirm the
capability of the constructed multi-core transmission line to
beyond 100 Tera-bit/s transmission, 16QAM(9) based 116-wavelength
signals were prepared and the output signal quality after 316 km
long transmission were examined.
Fan-In/Fan-Out devices(10) fabricated by NTT and Furukawa were used
to input/output signals to/from each core of multi-core fiber.
Pluggable optical connectors(11) with existing MU-type or SC-type
interfaces, fabricated by CIT and NTT, were used to connect the
input/output end of the multi-core transmission lines and
Fan-In/Fan-Out devices. These optical connectors have rotational
alignment features in order to connect the facing four-cores
correctly. Thus, the low loss and pluggable optical connection of
multi-core structure was achieved.
Satisfactory well transmission quality was confirmed in all cores
and all wavelengths, this result is the world's largest
transmission capacity of 118.5 Tera-bit/s(12) among a standard
diameter optical fiber. These achievements reveal that multi-core
fiber with standard diameter can be used to realize an ultra large
capacity transmission system overcoming the capacity crunch in the
current SMF.
http://www.acnnewswire.com/topimg/Low_NEC8817Fig4.jpg
Figure 4: Example of transmission experiments among a standard
diameter optical fiber
Future Prospects
The present achievement indicates that a multi-core fiber with the
standard diameter can be used to realize a transmission capacity of
more than 100 Tera-bit/s while enabling the productivity
improvement and effective use of the existing technology. This
achievement is expected to open up earlier practical use of the
multi-core fiber technology.
We will aim to introduce the standard diameter multi-core fiber by
the early 2020s. We will also continue to contribute the
realization of a future optical infrastructure which can support
variety of data communication demand.
(1) Tera-bit/s
Tera (Unit: T) corresponds to an amount of 1012. 100 Tera-bit
transmission enables us to transfer 500 blue-ray disks (25
Giga-byte/disk) at one second.
(2) A glass diameter in accordance with International standard
In accordance with the International standard, a glass and a
coating (including a glass and protection regions) diameters are
specified at 125+/-0.7 micrometer and 235-265 micrometer,
respectively in order to ensure an interconnection between optical
fibers provided by different vendors.
(3) Postdeadline paper
A technical paper that is received after the regular submission
deadline. In the optical communication research field, [research
groups from around the world submit their best results. A limited
number of papers that receive an extremely high evaluation in a
selection meeting held during the conference period are accepted
for presentation in the postdeadline session.
(4) Example achievements on multi-core fibers with 10-core or
more
(5) Loss of optical fiber
A 0.21 dB/km contains loss at splicing points. We spliced two
multi-core fibers by melting each end, namely fusion splice
technology. A 0.21 dB/km loss is comparable property obtained with
current optical fiber.
(6) Optical signal interference between neighboring cores
A small portion of an optical signal is transmitted outside the
core. This causes interference between different optical signals
and degrades the transmission quality when neighboring cores are
too close to each other.
(7) Mode field diameter (MFD)
A parameter which shows a diameter of optical signal propagating in
an optical fiber. MFD is an important parameter for ensuring the
interconnection of optical fibers provided by different
manufactures because larger difference in MFD results in the
connection loss increase.
(8) Multi-core optical amplifier using cladding pumping
In a cladding pumping based multi-core optical amplifier, pumping
light as an optical amplification source is injected into the
cladding region which contains multiple cores. The other hand core
pumping based multi-core optical amplifier uses multiple pumping
light in order to launch the amplification source light into each
core individually. The cladding pumping scheme is expected to
reduce the power consumption compared with that in the core pumping
scheme. In this achievement, a multi-core optical amplifier
fabricated by NEC realized a 16% power reduction in which core and
cladding pumping were well combined, so call a hybrid type
multi-core optical amplifier.
http://www.acnnewswire.com/topimg/Low_NEC8817Fig5.jpg
Figure 5: Image of a cladding pump based multi-core optical
amplifier and experimental result for power consumption
reduction
(9) 16QAM signal
Traditional optical communication uses intensity modulation in
which signals are sent using two distinct states ON and OFF to
correspond to digital 0's and 1's. 16QAM (Quadrature amplitude
modulation) signals are modulated by two independent optical signal
components, namely I- and Q-components, using the 4-th level. This
makes it possible to transfer 4x4 = 16 levels signals
simultaneously.
(10) Fan-In/Fan-Out device
A device which enables to connect between four-individual
conventional SMFs and four-cores in a multi-core fiber. In this
achievement, both fiber- and waveguide-type devices were used.
(11) MU-type and SC-type optical connector
A pluggable optical connection technology which has been used in
the current optical communication system. International standard
has specified MU-, SC-, FC-types and so on based on the shape of
connector.
http://www.acnnewswire.com/topimg/Low_NEC8817Fig6.jpg
Figure 6: Overview photos and optical connection image of MU-type
(top) and SC-type (bottom) optical connectors.
(12) World's largest 118.5 Tera-bit transmission
In this achievement, 116-wavelengths with a 36 Giga-Baud (Giga
corresponds to a 109), 16QAM (16-level = 24) modulation, and
polarization multiplexed (2-orthogonal polarizations) were
transmitted. A 12.75% bit were used for error correction, thus the
effective transmission capacity becomes a 118.5 Tera-bit as shown
below:
116-wavelengths x log216 x 2-polarizatoins x 4-core/1.1275 (error
correction) = 118.5 Tera-bit.
http://www.acnnewswire.com/topimg/Low_NEC8817Fig7.jpg
Figure 7: Transmission performance of 16QAM based 116-wavelengths
after a16-km transmission.
About NEC Corporation
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Source: NEC Corporation
Contact:
NEC
Seiichiro Toda
s-toda@cj.jp.nec.com
+81-3-3798-6511
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