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Photo credit: Getty Images/Tim Platt |
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Optical technologies are the driving force behind the
bandwidth growth of the Internet. Indeed, the Internet
as we know it would not be feasible without optical
technologies and the related networking standards.
This is made clear in “The Optical World”, a Technology
Watch Report published in June 2011 by ITU’s
Telecommunication Standardization Sector (ITU–T).
By enabling bandwidth hungry applications for video,
optical technologies have opened the way for new business
models such as YouTube, allowing users to share
video clips.
ITU–T standards in optical transport networks have
played a leading role in transforming the Internet’s
bandwidth capabilities. This work is led by ITU–T Study
Group 15, which has developed a set of international
standards (Recommendations) that defines the existing
optical transport network (OTN) framework. ITU–T
Study Group 15 is now working on future technologies
(such as gigabit-capable and 10-gigabit-capable passive
optical networks), anticipating unprecedented bandwidth
demands from service providers and consumers.
Optics is the science of light and has a very long history.
Optical networking, silicon photonics (light technology),
nanotechnologies and non-linear optics are all
areas where breakthroughs could lead to major changes
in the way computers, networks and data centres
are designed. The new ITU–T Technology Watch Report
provides an overview of the optical world, and surveys
standards and ongoing research that will lead to a new
generation of Internet and computing devices. Some of
the challenges the world faces in energy, health and the
environment may be solved with the help of optics and
photonics.
Why optical technology?
Today, the most widely used optical technology is
optical fibre for high-speed interconnections, such as
in server racks, connecting offices, buildings and metropolitan
networks — and even continents via submarine
cables. Optical technology is also used in CD-ROM
drives, laser printers, photocopiers and scanners. But
there are always some conventional electronic circuits
or components in these devices because, to date, high
costs have prevented optical components from finding
their way into computers.
Now that optical technology is maturing, prices are
falling and optical alternatives are starting to be incorporated
into computer systems. Compared with copper
wire and electronics, optical equipment has many
advantages for use in communication networks and
computers: less power consumed; higher speeds; more
compact; much lighter; cheaper to manufacture; higher
storage capacity; immune to electromagnetic interference;
free from short circuits; lower operational costs
for service providers; and reduced carbon footprint for
telecommunication.
Optical technology to meet broadband demand
The gradual incorporation of optical technology into
the world of traditional electronics is paving the way for
the era of the optical world. Industry experts see optical
technology as the most feasible means of solving
the bandwidth limitation of electronics. Photons have
low-loss transmission and provide large bandwidth, offering
multiplexing capacity for communicating several
channels simultaneously without interference. In terms
of speed, data travel through an electronic network at
megabits per second (Mbit/s), as compared to terabits
per second (Tbit/s) in photonic networks. The power
requirement for an electronic switching component is
about one microwatt, whereas the power requirement
for a photonic switching component is measured in
nanowatts.
The ever-increasing need for computational speed,
coupled with the rapid increase in global demand for
Internet access, television and video services, and nextgeneration
broadband, has focused interest on optical
computing technology. Service providers in the telecommunication
sector have transformed their offerings into
a new business model for triple-play services (combining
voice, data and video) that rely on sufficient bandwidth
to carry large amounts of data. As telecommunication
networks expand on a global scale, optical communication
will continue to be a strategic enabler for nextgeneration
Internet services.
Because of its advantages over electrical transmission,
optical fibre is rapidly replacing copper wire in core
networks in the developed world and is key for developing
countries in bridging the digital divide. The high frequency
of the optical carrier enables significantly more
information to be transmitted over a single channel
than is possible with a conventional radio or microwave
systems.
Communication networks using optical fibre still
need to convert the electrical signal into an optical one
for transmission, and then back into electrical form at
the receiving end. This means that the potential bandwidth
of optical fibres is not being fully exploited.
Future research and standardization work will focus on
developing purely optical devices for communication
networks.
Current and future standardization activities
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Optical transport networks: From timedivision multiplexing (TDM) to packet
The ITU–T manual “Optical Transport Networks:
from TDM to Packet”, launched in February 2011, is
based on the standards issued by ITU–T on optical
transport networks. It covers synchronous digital
hierarchy (SDH), optical transport network (OTN) and
Ethernet over transport (EoT) Recommendations,
which are now used in telecommunication networks.
The manual describes the problems associated with
implementing OTN structures, and shows how ITU–T
Recommendations address these challenges. It offers
practical help and guidance to operators, suppliers
and management in planning and implementing
OTN. The manual is available at:
http://www.itu.int/publ/T-HDB-IMPL.08-2010/en.
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Optical transport networks
Synchronous optical networking (SONET), adopted
as the backbone of most fibre-optic telecommunication
networks in the late 1990s, was originally designed
for optical interfaces that used a single wavelength
per fibre. As fibre-optic technology has advanced, it
has become more economical to transmit multiple
SONET signals over the same fibre. The optical transport
network (OTN) architecture for this is specified in
Recommendation ITU–T G.872.
OTN is the only transport layer in the industry that
can carry a full 10/40/100 Gbit/s Ethernet signal from
Internet Protocol (IP)/Ethernet switches and routers at
full bandwidth. It is composed of a set of optical network
elements connected by optical fibre links. The
OTN framework is based on a set of Recommendations
with ITU–T G.709 “Interfaces for the Optical Transport
Network (OTN)” at the heart.
Recommendation ITU–T G.709 describes a means of
communicating data over an optical network. Revised
in June 2010, it now provides a mapping of a recent
next-generation high-rate Ethernet standard from the
Institute of Electrical and Electronics Engineers (IEEE)
into OTN. Collaboration between ITU–T Study Group 15
and the IEEE P802.3ba 40 Gbit/s and 100 Gbit/s Ethernet
Task Force has ensured that these new Ethernet rates
are transportable over optical transport networks. A
manual on OTN highlights the applications of ITU–T
Recommendations in this field.
Optical communication systems reaching terabit
speeds could become the norm in the future. A
breakthrough in terms of data transfer speed in optical
communications was announced in the May 2011
issue of the Nature Photonics journal: researchers at
Karlsruhe Institute of Technology established a record
by transmitting 26 Tbit/s using a single laser. Optical
communications at terabit speed would be highly benefi
cial to bandwidth-hungry applications such as cloud
computing, three-dimensional television (3D TV), highdefi
nition television (HDTV) and virtual reality. The
breakthrough could pave the way for future standardization
work in this area.
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Optical fibres cables and systems
ITU–T has been active in the standardization
of optical communication technology and the
techniques for its optimal application within
networks from the infancy of this industry. Since
the first ITU–T Handbook related to optical fibres,
“Optical Fibres for Telecommunications”, published
in 1984, several others have been produced over the
years to keep pace with developments in the field.
The latest manual, “Optical fibres, cables and
systems”, was published in 2009. It aggregates
the available information on ITU–T’s work, and is
intended as a guide for technologists, middle-level
management and regulators. ITU–T also conducts
tutorials for developing countries based on the
manual, to provide an in-depth insight into the
application of its Recommendations in this field.
The manual aims to assist in the installation of
optical fibre-based systems, explaining how ITU–T
Recommendations address the practical issues
associated with the application of this technology.
The manual can be downloaded free of charge at:
http://www.itu.int/pub/T-HDB-OUT.10-2009-1/en.
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Automatically switched optical network
Backbone networks must offer quality of service and
flexibility. The purpose of the automatically switched
optical network (ASON) is to automate resource and
connection management within the network to preserve
quality of service. This will be a huge challenge because,
according to the annual Cisco Visual Networking
Index, global IP traffic was an estimated 242.2 exabytes
(1 exabyte = 1018 bytes = 1 billion gigabytes) in 2010
and is projected to increase to 965.5 exabytes by 2015.
The main issue in the area of standardization for
ASON has been the optical control plane. Work to define the standards for the optical control plane is being
investigated by international standards bodies, including
ITU–T, which is working on ASON architecture.
Controlling quality of service is one of the essential
elements for managed IP networks. ITU–T recently
achieved significant results, in cooperation with IEEE, in
standardizing the operations, administration and maintenance
functionality for Ethernet networks. This lies
at the core of IP packet transmission platforms and is
an essential technology for next-generation networks.
A recent manual highlights ITU–T Recommendations in
this field.
Passive optical networks
A passive optical network (PON) extends from an
operator’s central facility into individual homes, apartment
buildings and businesses. One common application
of PONs has been in providing broadband Internet
access to homes for applications such as IP television.
The advantage of PONs is that they offer high reliability
and high bandwidth at low cost. Some gigabitcapable
PON products already include a power-saving
mode, which reduces power consumption. The most
recent standard, G.984 (GPON), represents a significant
boost in total bandwidth and bandwidth efficiency,
through the use of larger, variable-length packets. A
GPON network delivers up to 2488 Mbit/s of downstream
bandwidth, and 1244 Mbit/s upstream.
Optical exchanges
Peering of regular Internet traffic has led to switching-based Internet exchanges. Optical exchanges on
the other hand will not require switching technology at
peering locations. With the fall in cost of optical devices,
they could become viable as components in Internet
exchange points. An optical exchange is a peering location
that allows traffic to pass from one provider to
another in a connection-oriented manner. An example
is NetherLight in Amsterdam.
The NetherLight Exchange Point is part of the Global
Lambda Integrated Facility (GLIF) network. GLIF is an international
organization that promotes optical networking
using lambda switching, which can switch individual
wavelengths of light onto separate paths for specific
routing of information.GLIF uses optical multiplexing
capabilities to provide the bandwidth needed for scientifi
c research and collaboration on a global scale. Sites
that form part of the GLIF network include CERNLight
(Geneva), UKLight (London), MoscowLight (Moscow),
and StarLight (Chicago).
Optical exchanges represent a new area of research
for packet-based optical networks that could provide
the backbone for grid computing.
Visible light communication
Visible light communication (VLC), using white light
emitting diodes (LEDs), is emerging as a key technology
for ubiquitous communication systems, because
LEDs have the advantages of fast switching, long life
expectancy, relatively low cost, and safety for the human
body.
The signal would be generated in a room by slightly
flickering all the lights in unison. People would not notice
this, because the rate of modulation would be millions
of times faster than a human eye can see. Since
visible light cannot penetrate walls, there would be no
interference from stray signals and reduced opportunity
for outside hackers, thus making the system more
secure than radio. In January 2010, Siemens researchers,
in collaboration with the Heinrich Hertz Institute in
Berlin, achieved a wireless data transfer rate of up to
500 Mbit/s using white LED light.
Infrared light could also be used in visible light communication.
The Infrared Data Association (IrDA) has
been developing technical standards for infrared wireless
communication and has recently announced the
GigaIR standard for very short range line-of-sight infrared
communication links operating at 1 Gbit/s. Speeds
of more than 1 Gbit/s have been obtained with infrared
light, according to research carried out by Penn State
University.
The Visible Light Communications Consortium
(VLCC) and IEEE 802.15 Task Group 7 have been active
in standardization work related to visible light communication.
Major applications would be in private
networks, home networks, sports broadcasts and live
television interviews, and in optical beacons for collection
of information in real time. In particular, applications
could include use in restricted areas where secure
access is important, the projection of high-definition images,
and use in aircraft and medical facilities (because
the optical system will not interfere with aircraft navigation
or hospital systems). Visible light communication
could also be used in global location positioning, to support
intelligent transport systems.
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Photo credit: AFP |
Apple’s Macbook Pro laptop that uses Intel’s Thunderbolt, a high-speed computer connection technology formerly codenamed Light Peak.
This new technology is said to move digital films and other data “blazingly fast” |
Optical data transfer inside the computer
New data transfer technology based on optical fibres will lead to dramatic advances in the performance
and design of computers. An example is Thunderbolt
(originally codenamed Light Peak), a technology that
has been developed by Intel to give ordinary personal
computers the ability to connect with other devices using
high-speed fibre-optic cables at 10 Gbit/s — twenty
times faster than a standard, copper-based USB 2.0
cable. An optic cable can drive a high-definition (HD)
display or transfer an HD movie in seconds. Thunderbolt
has been implemented in 2011, for example, in the new
line of Apple’s MacBook Pro laptops.
Silicon photonics
The use of multi-core central processing units is one
way of controlling power consumption in high-performance
electronic circuits. And the low cost and high
availability of silicon make it the material of choice for
optoelectronic devices. Silicon photonics involves integrating
optical and electronic circuits on silicon.
In August 2010, Intel announced the first complete
photonic communication system developed from components
fully integrated into silicon chips. Silicon photonic
chips could, for instance, replace the electronic
components between a computer memory and processor.
They allow for the processor and memory to be
further apart than is possible with copper wiring, and
could change the way computer systems, laptops and
data centres are designed.
The main challenge for silicon photonics is growing
the laser on a silicon chip, because silicon is a poor laser
material. In February 2011, however, researchers at the
University of California announced that they had overcome
this problem by taking advantage of the properties
of nanostructures and by carefully controlling the
growth process. This is the first time that researchers
have grown lasers from high-performance materials directly
on silicon.
Optical bus
IBM announced in 2010 that it had successfully developed
an optical data bus on a printed circuit board
that uses optical links for data transfer between the processor
and other external components such as memory
and input/output ports. By avoiding the signal-loss and
cross-talk problems associated with copper, an optical
bus would make supercomputers much faster. IBM is
planning to use the optical bus in supercomputers for
optical data transfer between printed circuit boards.
IBM is also conducting research aimed at developing
parallel optical interconnects, referred to as optochips,
which will enable ultra-fast data transfer between the
components on the printed circuit board. The optochips
are transceivers that convert the signal from electrical
to optical and back again. IBM expects that within five
years, the optochips will find their way into the supercomputer,
replacing copper wiring as the connection
between processors and memory.
All-optical computers
Light can be used to transmit, record and process
information, and researchers are attempting to develop
entirely new methods of computing that are not physically
possible with electronics.
The main building block of conventional computers
is the electronic transistor. In order to build an optical
computer, an equivalent optical transistor is required.
Over short distances, photons consume more energy
than electrons in information processing and transmission.
To overcome that challenge, researchers are exploring
non-linear optical technology.
Another emerging field of research involves silicon
nanowires, which can guide light like optical fibres.
Because of their low power consumption and size,
nanowires are expected to be used in areas such as
implantable medical monitors that must be small and
where fast processing is not needed.
Research on developing an all-optical computer is a
multidisciplinary arena, involving topics such as biophotonics
and nanophotonics. A new paradigm is needed
for packaging all-optical components. Until this process
is standardized so that the optical transistor equivalent
can be mass produced, the optical computer will remain
a dream.
The way forward
Standardization work in ITU is already engaged in
the evolution towards an all-optical core network for
Internet and other telecommunication services. A workshop
is proposed to showcase the developments made
and outline the future evolution of the optical network.
As optical devices become more commonplace, security
will need to evolve into the optical domain, with
firewalls and intrusion prevention systems. Along with
the all-optical computer, a new area of study will be the
energy-efficient optical network, because of its importance
in reducing the carbon footprint of telecommunication
and in protecting the environment.
* The ITU–T Technology Watch Function surveys the information
and communication technology (ICT) landscape to capture
new topics for standardization activities. Technology Watch
Reports assess new technologies with regard to existing
ITU–T and other standards, and the likely implications for
future standardization. The Technology Watch Function is
managed by the Policy and Technology Watch Division of
ITU’s Telecommunication Standardization Bureau. The report
“The Optical World” and other Technology Watch Reports are
available at: http://www.itu.int/ITU-T/techwatch
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