POORNIMA INSTITUTE OF ENGINEERING AND TECHNOLOGY

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POORNIMA INSTITUTE OF ENGINEERING AND TECHNOLOGY
Department of Electronics and Communication
Arrayed Waveguide Gratings Based dwdm
Presented By Sachin Agrawal B.Tech -IV year
Guided by Mr. K. R. Prajapat
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CONTENTS
INTRODUCTION
OVERVIEW OF ARRAYED WAVEGUIDE GRATINGS
DWDM
APPLCATIONS AND DESIGN
CONCLUSION
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OPTICAL COMMUNICATIONS

• Optical Fiber is a popular carrier of long
  distance communications due to its
• potential speed,
• flexibility and
• reliability.

• Although, reality was different
• Attenuation and dispersion problems in fiber,
  limits the practical speed and distance of
  communication.

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• Partially resolved with the advent of the Erbium
  Doped Fiber Amplifier (EDFA)
• Eliminating problems caused by attenuation
• The dispersion qualities of an optical fiber
  still force a compromise between transmission
  distance and bandwidth,
• Making it necessary to refresh high-speed signals
  at intervals using opto-electronic repeaters

Solving the dispersion problem in this manner is
expensive, due to the additional cost of
high-speed electronics, and maintaining and
upgrading the link is made more difficult and
costly (especially with a buried or under-water
link).
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DENSE WAVELENGTH DIVISION MULTIPLEXING (DWDM)
More elegant solution is found using DENSE
WAVELENGTH DIVISION MULTIPLEXING (DWDM), which
effectively increases the useable bandwidth in a
system without electronic repeaters, and allows
realization of a true photonic network
Dense wavelength division multiplexing (DWDM) is
a fiber-optic transmission technology to combine
multiple optical signals operating at different
wavelengths into a single fiber. This technology
allows the capacity of an optical fiber to
increase dramatically.
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• Each channel, since it is effectively separated
  from the others, can be independent in protocol,
  speed, and direction of communication.
• DWDM also helps realize an all-optical network
  architecture where signals are routed according
  to wavelength without the need for
  electro-optical conversion.
• As a result, this type of network is potentially
  faster and more flexible
• Can be less costly to maintain when compared to
  other methods.

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ARRAYED WAVEGUIDE GRATING (AWG) OPERATION
PRINCIPLES
Arrayed Waveguide Gratings (AWGs) are optical
wavelength (de)multiplexers used in DWDM. As well
as performing basic (de)multiplexing functions,
they can be combined with other components to
create add/drop Multiplexers. The Arrayed
Waveguide Grating (AWG) plays a crucial role in
the realization of modern optical networks.
Structure of The AWG
The input (a) consists of several channels,
typically between 8 and 40 in commercial devices,
carried on separate frequencies. Channel spacing
of 100GHz or 50 GHz are common in
commercial Devices. The operational wavelength
is commonly around 1.55µm where attenuation is
lowest in optical fibers.
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PRINCIPLE OF DWDM TECHNOLOGY

• In normal optical link there is one optical
  source at transmitting end and one photo detector
  at receiving end.
• Signals from different light sources use separate
  and unique assigned fiber for transmission of
  signal.
• As the spectral bandwidth of the laser source is
  very narrow, this type of transmission makes use
  of only a small portion of the entire optical
  band and remaining portion of the band is not
  used.
• In DWDM technology, the different light sources
  are first converted to pre-assigned wavelength
  according to the DWDM standards and then combined
  in such a manner that they occupy different
  portion of the available optical band.
• In between the two optical signals suitable guard
  band is also left, so that there is no
  interference from adjacent channels.
• Thus DWDM technology makes use of the entire
  optical bandwidth.

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DWDM FUNCTIONAL SCHEMATIC
The system performs the following main
functions.   Generating the signal The source,
the solid state laser, must provide stable light
within the specific, narrow band width that
carries the digital data, modulated as an analog
signal.   Combining the signals Modern DWDM
systems employ multiplexers to combine the
signal. There is some inherent loss associated
with multiplexing and demultiplexing. These loss
is dependent upon the number of channel but can
be mitigated with optical amplifiers, which boost
all the wavelengths at once with out electrical
conversion.   Transmitting the signals The
effect s of cross talk and optical signal
degradation or loss must be reckoned with in
fiber optic transmission.   Separating the
signals At the receiving end, the multiplexed
signals must be separated out. Although this task
would appear to be simply the opposite of
combining the signals.    Receiving the signals
The demultiplexed signals is received by photo
detectors.
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DENSE WAVELENGTH DIVISION MULTIPLEXING (DWDM)
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An Add/Drop Multiplexer (ADM). Made
reconfigurable by using space division switches
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An Optical Cross Connect (OXC) employing a space
division switch for each wavelength. Switch
settings determine where each wavelength is
routed.
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DWDM SYSTEM ARCHITECTURE

• For A typical 8-channel DWDM system.
• The main components are, 
• TP (transponders)
• VOA (variable optical attenuator)
• MUX (multiplexer)
• DE MUX (de multiplexer) OPTICAL FIBRE
• AMPLIFIERS
• Erbium-dropped fiber optic amplifier
• Booster amplifier
• Pre-amplifier
• Line amplifier 
• Optical add-drop multiplexer (OADM)

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8-CHANNEL DWDM SYSTEM
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TRANSPONDERS

• This unit interfacing wide pulse optical signal
  and MUX/DMUX equipment. It converts the wide
  pulse signal into a narrow wavelength of the
  order of 1.6nm, sending to MUX.
• In the reverse direction, colored output from
  DMUX is converted to wide pulse optical signal.
•  
•  

VARIABLE OPTICAL ATTENUATOR
This is a passive network like pre-emphasis
required to adjust for uniform distribution of
signal level over EDFA band so that individual
channel optical output power of MUX unit remain
same irrespective of the number of channels being
loaded in the system.
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COMBINER SPLITTER
The DWDM system transmits several optical signals
over a single fiber. All the signals are combined
at the transmission end and again split at
receiving end. The combining is done by combiner,
also called multiplexer and splitting is done by
splitter, also called demultiplexer.
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OPTICAL FIBRE AMPLIFIER
In DWDM technology optical amplifiers are used
instead of electrical amplifier. Thus pulse
shaping and retiming functions are not done at
repeater stations.
ERBIUM DOPED FIBRE AMPLIFIER (EDFA)

• It consists of doped fiber (10 to 50mlong), one
  or more pump lasers, a passive wavelength
  coupler, optical isolators and tap couplers.
• The tap couplers are wavelength insensitive with
  typical splitting ratio ranging from 991 to
  955.
• They are generally used on both sides of the
  amplifier to compare the incoming signal with the
  amplified output.
• The optical isolators prevent the amplified
  signal from reflecting back into the device
• otherwise it could increase the amplifier noise
  and decrease the efficiency.

EDFAs are widely used in DWDM system for
amplification of optical signals. Erbium is a
rare earth element and emits light around 1550 nm
region when it is exited. Thus it is most suited
for DWDM operations as DWDM also makes use of
1550nm window.
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• Depending upon the gain, EDFAs are classified
  into following three categories.
• For long haul application.
• For very long haul application.
• For ultra long haul application.

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• BOOSTER AMPLIFIER
•  
• It is basically an EDFA amplifier which boost the
  entire wide band optical signal coming from the
  out put of MUX.
• Here the total output power booster amplifier is
  constant irrespective of the number of channels
  being loaded to the system.
• Line is connected to the amplifier for
  transmission of signal to the distant end
  supporting the optical safety operation.
•  
• LINE (OFC MEDIA)
•  
• This is the optical fiber media over which the
  DWDM signal travel. Attenuation and dispersion
  are the main limitation factors determining
  transmission distance and bit rate capacity etc.
• Normally 22dB and 33dB are taken as the line
  loses for hop length of long haul and very long
  haul system respectively.

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• LINE AMPLIFIERS
•  
• It is two stage (EDFA) amplifier consisting of
  pre-amplifier and booster amplifier. With out two
  stages it is not possible to amplify the signal
  up to 33dB on EDFA principle avoiding large ASE
  (amplifier spontaneous emission) noise.
•  
• PRE-AMPLIFIERS
•  
• This amplifier along is used at the terminal to
  interface the DEMUX and line for receiving coming
  from the distant station. Hence the attenuated
  line signal is amplified to a level of 3dBm to
  10dBm before entering into DEMUX unit.
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• OPTICAL SUPERVISORY CHANNEL (OSC)
•  
• The function of transmission of additional data
  at a separate wavelength of lower optical power
  with out any optical safety provision,
  accompanied with and independent of the main
  optical traffic signal, is performed by this OSC.
• The OSC helps management to control and monitor
  the optical line devices.
• The management for fault location, configuration,
  performance and security.

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OPTICAL ADD/DROP MULTIPLEXER (OADM)   Adding or
dropping of channels at optical level is possible
by using optical add/drop multiplexer module. It
is a unidirectional module with facility for
dropping or adding optical channel of specific
wavelength. The dropping and adding of the
optical wavelength this performed with fixed
optical filters. With the help of OADM module it
is possible to insert or drop maximum for optical
wave lengths at any intermediate stations.
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ADVANTAGES OF DWDM TECHNOLOGY

• The capacity of transmission media can be
  upgraded easily by using DWDM technology. The
  capacity of existing DWDM system can be upgraded
  by deploying higher channel capacity system.
  Thus, The need of laying new fibers for
  increasing capacity of transmission media is
  avoided.
• Bit rate transparency in DWDM system, optical
  channels can carry any transmission format. thus
  the different wavelengths from different systems
  can be transmitted simultaneously and
  independently over the same fiber. Thus DWDM
  system can transport any type of optical signal
• Quick deployment The DWDM technology is,
  generally, deployed using existing fibers. The
  time required for laying new fiber is much more
  as compared to equipment deployment time. hence,
  the deployment of dwdm systems can be done
  quickly.

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• Economical The DWDM system is cheaper as
  compared to overall cost of laying new fiber for
  increasing transmission capacity. In DWDM system,
  one optical amplifier is used for amplification
  of all the channels, hence per channel cost is
  drastically reduced .
• Wavelength routing In DWDM system, by using
  wavelength sensitive optical routing devices, it
  is possible to route any wavelength to any
  station. Thus it is possible to use wavelength as
  other dimension, in addition to time and space in
  designing transmission network.
• Wavelength switching In DWDM system, wavelength
  switching can be accomplished by using OADM,
  optical cross connect and wavelength
  converters.thus, it is possible to reconfigure
  the optical layer using wavelength switched
  architecture.

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• DISADVANTAGE
•  
• Protection and maintenance in DWDM system is
  very hard
• DWDM systems have to maintain more stable
  wavelength or frequency
• Precision temperature control of laser
  transmitter is required in DWDM systems to
  prevent "drift" off a very narrow frequency
• DWDM associated with higher modulation rates so
  it makes costly operation
• DWDM provides maximum capacity so it tends to
  be used at a higher level in the communications
  hierarchy

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APPLICATIONS

•  

•  Multiplexes more than 400 channels at a time
• Faster than time division and frequency division
  multiplexing
• Mostly used in fiber optic transmission
• Transmission of e-mail, video, multimedia, data,
  and voice
• Asynchronous transfer mode (ATM)

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CONCLUSION

•  
• The demand of bandwidth is increasing day by
  day, especially for data traffic.
• Service providers are required to provide the
  bandwidth dynamically and in shortest possible
  time.
• This can only be done by DWDM. In future
  advanced DWDM components will be
  available.
• Thus, it will be possible to manage the optical
  signal dynamically, which will allow more
  flexibility to the service providers.

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REFERENCES

• Shri H. Saha, Shri Nural Anowar, DWDM System
  Testing Telecommunication March April 2002
• P.K. Pandy, Dense Wave Length Division
  Multiplexing Telecommunication November December
  2002
• DWDM Multiplexing, IEEE Transactions on Volume
  7, Issue 4, July 2008.
• A paper on Array Waveguide Grating, Department of
  Communication
• www.canon.com
• www.thoshiba.com
• www.electronics.howstuffworks.com
• www.howstuffworks.com

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QUERIES ?
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