1. POORNIMA INSTITUTE OF ENGINEERING AND TECHNOLOGY
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Department of Electronics and Communication
Arrayed Waveguide Gratings Based dwdm
Presented By: Sachin Agrawal B.Tech -IV year
Guided by: Mr. K. R. Prajapat

2. CONTENTS INTRODUCTION OVERVIEW OF ARRAYED WAVEGUIDE GRATINGS DWDM
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INTRODUCTION
OVERVIEW OF ARRAYED WAVEGUIDE GRATINGS
DWDM
APPLCATIONS AND DESIGN
CONCLUSION

3. OPTICAL COMMUNICATIONS
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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.

4. Eliminating problems caused by attenuation
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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).

5. 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
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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.

6. Can be less costly to maintain when compared to other methods.
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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7. ARRAYED WAVEGUIDE GRATING (AWG) OPERATION PRINCIPLES
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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.

8. PRINCIPLE OF DWDM TECHNOLOGY
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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.

9. 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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10. DENSE WAVELENGTH DIVISION MULTIPLEXING (DWDM)
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11. An Add/Drop Multiplexer (ADM). Made reconfigurable by using space
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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.

13. 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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14. 8-CHANNEL DWDM SYSTEM
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15. VARIABLE OPTICAL ATTENUATOR
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.
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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.

16. COMBINER & SPLITTER
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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.

17. 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.
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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 99:1 to 95:5.
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.

18. For long haul application. For very long haul application.
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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19. 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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20. OPTICAL SUPERVISORY CHANNEL (OSC)
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.
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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21. 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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22. ADVANTAGES OF DWDM TECHNOLOGY
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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.

23. 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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24. Protection and maintenance in DWDM system is very hard
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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25. Multiplexes more than 400 channels at a time
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 , video, multimedia, data, and voice
Asynchronous transfer mode (ATM)
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26. 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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27. DWDM Multiplexing, IEEE Transactions on Volume 7, Issue 4, July 2008.
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
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QUERIES ?

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