Tokyo and Kawasaki, Japan, October 13, 2011 - Fujitsu Limited and Fujitsu Laboratories
Limited today announced the development of optical amplifier technology for use in optical
access systems that link subscribers to central offices. The new optical amplifier
technology has the ability to quadruple the splitting number and double transmission
distance.
The use of optical aggregation networks, in which optical signals between a central office
and many subscribers are optically passed along, rather than converted into electrical
signals, has been proposed as one way to reduce the constantly growing amount of electrical
power consumed by networking equipments. Although passive optical networks (PONs) (1),
which increase transmission speeds in both downstream and upstream from the prevailing
speed of 1 Gbps to 10 Gbps, are now starting to be deployed commercially, there are
constraints in using them for optical aggregation networks because the number of optical
network terminals (ONTs) for the most commonly used PON is typically limited to 32
connections and its transmission distance is also limited around 20 km.
To address these constraints, especially in upstream bursts(2), Fujitsu and Fujitsu
Laboratories have developed a burst-mode optical amplifier technology with a semiconductor
optical amplifier (SOA)(3), an integrated SOA-array(4) module fabrication technology, and
an SOA chip fabrication technology enabling uncooled operation. These three technologies,
used together, make it possible to quadruple the splitting number in an optical access
system and double the transmission distance between the central office equipment and the
terminal equipment.
This makes it possible for a next-generation optical access system to be used as an optical
aggregation network at low cost and with low power consumption requirements, paving the way
for cloud infrastructure. The research results achieved by the Commissioned Research of
National Institute of Information and Communications Technology (NICT) have been applied
to portion of this work.
Details of these technologies were presented at the 37th European Conference and Exhibition
on Optical Communication Conference (ECOC2011), held in Geneva, Switzerland from September
18 to 22.
<Background>
As we move into the era of cloud computing, in which a large volume of terminal equipment
and devices are connected to the network, technologies that allow for low-cost, low-power,
and long-distance connections are becoming indispensable.
With the increase in traffic over the Internet, the increasing amount of electrical power
consumed by routers and other networking hardware is becoming a pressing issue. The use of
optical aggregation networks has been proposed as one way of reducing power requirements.
In an optical aggregation network, many small routers that make up today's network could
be consolidated into a relatively few large routers, which would connect to many users
over optical fibers. This holds the potential to greatly reduce power consumption.
<Technological Issues>
While PONs, which increase transmission speeds tenfold to 10 Gbps, from today's prevailing
level of 1 Gbps, are coming into commercial use, there are obstacles in applying them to
optical aggregation networks in that the most commonly used PON is typically limited to
32 connections and its transmission distance is limited around 20 km. These figures need
to be improved in order for the technology to serve a sharply increasing number of users
at low cost.
<About the Three Newly Developed Technologies>
The three technologies that Fujitsu and Fujitsu Laboratories have developed make it
possible to implement improved upstream burst transmission characteristics, which needed
to expand the scope of optical access systems. This, in turn, quadruples the number of
ONTs an optical access system can support, and doubles the transmission distance between
the central office's equipment; optical line terminal (OLT) and ONT.
The newly developed technologies are as follows.
1. Burst-mode optical amplification
One method that has been considered for increasing the number of ONTs is the installation
of optical amplifiers in remote nodes(5) that lie between OLT and ONT, which would
compensate for fiber and splitting losses (Figure 1). The technology announced here is for
an amplifier that detects an incoming upstream burst and rapidly switches its "off"-state
to "on"-state for amplification. Whereas, conventionally, there would be multiple
continuous "on"-state optical amplifiers installed, with a proportionate amount of noise
making the optical signal-to-noise ration worse, the new technology turns on only the
optical amplifier with an incoming upstream burst. This means, for example, that even
with four optical amplifiers installed in the remote node (where each optical amplifier
equipped to 32-way split), up to 128-way split can be supported with the same amount of
the optical signal-to-noise ratio as 32 (Figure 2).
2. Integrated SOA-array module fabrication
In an industry first, integrated four semiconductor optical amplifiers are fabricated into
a single module (Photograph in Fig. 2). The Newly-developed optical coupling scheme
simultaneously couples four SOAs with four single mode fibers with high efficiency, which
reduces cost and footprint per piece.
3. SOA chip fabrication enabling uncooled operation for small footprint and power-saving
An aluminum composite material is deployed in the active layer of the semiconductor optical
amplifier to obtain high gain, even at high temperatures, eliminating the temperature
control of SOA (Photograph in Fig. 1). This dramatically contributes to the reduction of
the module volume to one-fifth and one-sixth the power compared with a conventional cooled
SOA module. It operates at temperatures of up to 85°C, so it can be installed outdoors on
utility poles or in street gutters, allowing for remote nodes that need to operate under
harsh conditions.
<Results>
With this technology, a next-generation access system applied to optical aggregation
networks can have 128 terminal-equipment connections, four times today's splitting number,
with distances of over 40 km, double today's distance.
Future Plans
Fujitsu will continue with research and development into optical aggregation networks using
this technology, and plans to extend it to cloud networks to accommodate traffic more
efficiently.
<Glossary and Notes>
1. Passive optical network (PON):
Used in optical subscriber networks and mobile backhauls.
2. Upstream burst:
PONs have one-to-many connections between the central-office transmission equipment and many
terminal equipments, and each terminal equipment sends optical signals to the central office
in bursts of 1-100 microseconds during the allowed time-slot in order not to interfere with
each other.
3. Semiconductor optical amplifier (SOA):
Uses compound semiconductors, for which amplification performance varies greatly with
temperature, so that cooling components are mounted within the module, and SOAs are used
under temperature control.
4. Integrated SOA-array:
An SOA chip that integrates multiple SOAs into an array.
5. Remote node:
A node comprising an optical coupler splitting/multiplexing signals and an optical amplifier,
placed between a central office and terminal equipments.
<About Fujitsu>
Fujitsu is a leading provider of information and communication technology (ICT)-based business
solutions for the global marketplace. With approximately 170,000 employees supporting
customers in over 100 countries, Fujitsu combines a worldwide corps of systems and services
experts with highly reliable computing and communications products and advanced
microelectronics to deliver added value to customers. Headquartered in Tokyo, Fujitsu Limited
(TSE:6702) reported consolidated revenues of 4.5 trillion yen (US$55 billion) for the fiscal
year ended March 31, 2011. For more information, please see: www.fujitsu.com.
<About Fujitsu Laboratories>
Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited, Fujitsu Laboratories Limited
is one of the premier research centers in the world. With a global network of laboratories in
Japan, China, the United States and Europe, the organization conducts a wide range of basic
and applied research in the areas of Next-generation Services, Computer Servers, Networks,
Electronic Devices and Advanced Materials. For more information, please see:
http://jp.fujitsu.com/labs/en/.
<Press Contacts>
Fujitsu Limited
Public and Investor Relations Division
Inquiries: https://www-s.fujitsu.com/global/news/contacts/inquiries/index.html
All other company or product names mentioned herein are trademarks or registered trademarks
of their respective owners. Information provided in this press release is accurate at time of
publication and is subject to change without advance notice
