04-08-2012, 02:19 PM
Optical Switching
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INTRODUCTION
Explosive information demand in the internet world is
creating enormous needs for capacity expansion in next generation
telecommunication networks. It is expected that the data- oriented
network traffic will double every year.
Optical networks are widely regarded as the ultimate solution
to the bandwidth needs of future communication systems. Optical
fiber links deployed between nodes are capable to carry terabits of
information but the electronic switching at the nodes limit the
bandwidth of a network. Optical switches at the nodes will overcome
this limitation. With their improved efficiency and lower costs,
Optical switches provide the key to both manage the new capacity
Dense Wavelength Division Multiplexing (DWDM) links as well as
gain a competitive advantage for provision of new band width hungry
services. However, in an optically switched network the challenge lies
in overcoming signal impairment and network related parameters. Let
us discuss the present status, advantages and challenges and future
trends in optical switches.
OPTICAL FIBERS
A fiber consists of a glass core and a surrounding layer called
the cladding. The core and cladding have carefully chosen indices of
refraction to ensure that the photos propagating in the core are always
reflected at the interface of the cladding. The only way the light can
enter and escape is through the ends of the fiber. A transmitter either
alight emitting diode or a laser sends electronic data that have been
converted to photons over the fiber at a wavelength of between 1,200
and 1,600 nanometers.
Today fibers are pure enough that a light signal can travel for
about 80 kilometers without the need for amplification. But at some
point the signal still needs to be boosted. Electronics for amplitude
signal were replaced by stretches of fiber infused with ions of the rareearth
erbium. When these erbium-doped fibers were zapped by a pump
laser, the excited ions could revive a fading signal. They restore a
signal without any optical to electronic conversion and can do so for
very high speed signals sending tens of gigabits a second. Most
importantly they can boost the power of many wavelengths
simultaneously.
Now to increase information rate, as many wavelengths as
possible are jammed down a fiber, with a wavelength carrying as
much data as possible. The technology that does this has a name-dense
wavelength division multiplexing (DWDM ) – that is a paragon of
technospeak.
Switches are needed to route the digital flow to its ultimate
destination. The enormous bit conduits will flounder if the light
streams are routed using conventional electronic switches, which
require a multi-terabit signal to be converted into hundreds of lowerspeed
electronic signals. Finally, switched signals would have to be
reconverted to photons and reaggregated into light channels that are
then sent out through a designated output fiber.
The cost and complexity of electronic switching prompted to
find a means of redirecting either individual wavelengths or the
entire light signal in a fiber from one path way to another without the
opto-electronic conversion.
OPTICAL SWITCHES
Optical switches will switch a wavelength or an entire fiberform
one pathway to another, leaving the data-carrying packets in a
signal untouched. An electronic signal from electronic processor will
set the switch in the right position so that it directs an incoming fiber –
or wavelengths within that fiber- to a given output fiber. But none of
the wavelengths will be converted to electrons for processing.
Optical switching may eventually make obsolete existing
lightwave technologies based on the ubiquitous SONET (Synchronous
Optical Network) communications standard, which relies on
electronics for conversion and processing of individual packets. In
tandem with the gradual withering away of Asynchronous Transfer
Mode (ATM), another phone company standard for packaging
information.
Optical Switches
Optical Switching
MEMS
Introduction
Micro-electro Mechanical Systems or MEMS is a new
process for device fabrication, which builds “micromechines” that are
finding increasing acceptance in many industries ranging form
telecommunications to automotive, aerospace, consumer electronics
and others.
In essence, MEMS are Mechanical Integrated circuits, using
photo lithographic and etching processes similar to those employed in
making large scale integrated circuits – devices that are deposited and
patterned on a silicon-wafer’s surface.
Construction
In MEMS, oxide layers are etched away to sculpt the device’s
structural elements. Instead of creating transistors, though,
lithographic processes built devices a few tens or hundreds of microns
in dimension that move when directed by an electrical signal. Silicon
mirrors are manufactured by self-assembly- a novel step that takes its
name from the way amino-acids in protein molecules fold themselves
into three-dimensional shapers. In the final stage of manufacture, tiny
springs on the silicon surface release the mirrors and a frame around
each on lifts them and locks them in place, positioning them high
enough above the surface to allow for a range of movement.