This document provides an overview of advances in optical fiber communication systems, including WDM, DWDM, SONET, and OTNs. It describes the basic principles and components of each technology. WDM and DWDM increase bandwidth by transmitting multiple wavelengths of light simultaneously over the same fiber. SONET provides a standard for fiber transmission and synchronization. OTNs were designed to transport IP and Ethernet traffic over optical networks.

1. Branch : Electronics & Communication Engineering
Sub : Optical Communication(2161005)
Topic : “Advances in Optical Fiber System”
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2. CONTENT
• Introduction
• WDM (Wavelength Division Multiplexing)
- Principle of operation
- Features of WDM system
• DWDM (Dense Wavelength Division Multiplexing)
- Necessity of DWDM
- Principle of operation
- Advantages of DWDM system
• SONET (Synchronous Optical Network)
- SONET frame/Network
- Applications of SONET
• OTNs (Optical Transport Networks)
- Features
- Architecture
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3. INTRODUCTION
• Optical telecommunication, is communication at a distance
using light to carry information. It can be performed
visually or by using electronic devices.
• High-speed optical communication is useful in
telecommunication systems, data processing and
networking. It consists of a transmitter that encodes a
message into an optical signal, a channel that carries this
optical signal to its desired destination, and a receiver that
reproduces the message from the received optical signal.
• Advance methods in optical communication systems are
WDM, DWDM, SONET, OTNs and switching.
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4. WDM (Wavelength Division
Multiplexing)
 Principle of operation :
• Four light sources emits the four wavelength of lights as shown.
• Optical multiplexer is used at the input side to multiplex these
signals.
• A demultiplexer is used at the output side to differentiate the
signals of equal amplitude.
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5.  WDM Network Architecture:
 The different WDM network elements like optical line
terminals (OLT), optical Add Drop Multiplexer (OADM),
optical Cross Connects (OXC).
 In fig. operating wavelength λ₁ is shown by a solid dotted
line and wavelength λ₂ is shown by dotted line.
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6.  Features of WDM architecture:
i. Wavelength reuse
ii. Wavelength conversion
iii. Transparency
iv. Circuit switching
v. Survivability
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7. DWDM (Dense Wavelength
Division Multiplexing)
• Dense Wavelength Division Multiplexing is a technology
that puts data from different sources together on an optical
fiber with each signal carried at the same time on its own
separate light wavelength.
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8. Necessity of DWDM:
• Due to the effect of bandwidth; always a compromise is
required between transmission distance and the bandwidth.
• So, it is required to use repeaters, after a certain distance,
all along the length of optical cable. This increases the total
cost of the system.
• DWDM increases the bandwidth of systems, without using
the repeaters.
• EDFA (Erbium Dopped Fiber Amplifier) are commonly
operated in range of wavelengths 1525 nm to 1565 nm and
DWDM are used in the band of 1550 nm. So, DWDM
increases the capabilities of EDFA.
• The DWDM increases the bandwidth and it supports for
more transmission distance. 8

9. Principle of operation:
• The DWDM, divides the light travelling through optical
cable into different wavelength. Each wavelength is called
lambdas.
• DWDM selects the wavelength in certain band. It is around
1550 nm and it is called as operating window of DWDM.
• Thus DWDM increases the capabilities of existing optical
network without extra cabling.
• Thus, using DWDM the different signals can travel in
parallel as if they travel in dedicated lanes, where each lane
is independent.
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10. DWDM System Structure
• The DWDM system structure consist of following
components :
1. Laser transmitter:
• The different laser sources transmitting laser beams at
accurate wavelength.
• Each laser sources, transmits different wavelength and all
wavelength from individual laser sources are closely
spaced.
2. Receiver:
• These are optical detectors, which receives the signal and
transmit them into demultiplexer.
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11. 3. EDFA:
• It is eribium dopped fiber amplifier. It is a silica based
optical fiber and it is dopped with eribium.
• EDFA acts as a repeater and it is used to amplify
incoming optical signal.
4. OADM:
• These are the components which receives an optically
multiplexed signal and these components can add or drop
a certain wavelength.
5. DWDM MUX:
• It is DWDM multiplexer, which receives many optical
signals of different wavelength; and transmit it on a single
optical cable.
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12. 6. DWDM DEMUX:
• It receives all signals on single cable and transmit each
wavelength in different cable.
• The laser sources transmit different wavelength which are
applied to the multiplexer.
• The different fibers carry these wavelength to the multiplexer.
The multiplexer, combine all these wavelength and transmit it
on a single optical fiber cable (OFC). 12

13. • OADM can takes certain wavelengths of its channel or add
certain wavelength form other optic channel. It can also
drop certain wavelength from main optical cable to another
optical channel.
• EDFA is used to amplify the signals. The output of EDFA is
connected to demultiplexer which separate out the different
wavelength.
 Advantages of DWDM:
• DWDM increases the bandwidth capability of the channel.
• Using DWDM, it is possible to use signals having different
data rates and different formats.
• A large amount of information can be transmitted
simultaneously.
• DWDM can handle higher data rates. 13

14. SONET (Synchronous Optical
Network)
• SONET being a synchronous network requires a single
clock to handle the timing synchronization and equipment
across the network.
• SONET is a multiplexed transport mechanism and hence
can be the carrier for broadband services such as ATM and
B-ISDN.
• SONET is basically a Time Division Multiplexing system.
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15. SONET Devices:
• There are three basic SONET devices.
1. Synchronous Transport Signal(STS) multiplexer
2. Regenerators
3. Add/drop multiplexer
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16. • The STS multiplexer multiplexes signals for various sources
into an STS or it demultiplexes an STS signal into various
destination signals.
• The STS signal passes through a number of regenerators or
repeaters while travelling from the source to destination.
• The regenerators are basically repeaters and are bidirectional
devices.
• The add/drop multiplexer is capable of adding signals from
various sources or it can remove any signal and redirect it
without demultiplexing the entire multiplexed signal.
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17. Applications of SONET:
• SONET can be used as carrier for ISDN and B.ISDN
• SONET can be used as carrier for ATM cells.
• SONET can be used for applications which provide
bandwidth on demand.
• SONET can be used for cable TV network.
• SONET can be used to replace the existing T-1 or T-3
lines.
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18. OTNs (Optical Transport Network)
• OTNs is basically designed for transportation of IP and
ethernet over optical cables.
Features:
1. Forward Error Correction (FEC)
2. Management
3. Protocol Transparency
4. Asynchronous timing
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19. Architecture
• The different layers of OTN are shown in fig.
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20. • The layers are divided into groups, namely optical layer and
electronic layer.
• Optical layer consist of:
1. Optical transmission section (OTS)
2. Optical multiplexed section (OMS)
3. Optical channel (OCh)
• OTS section provides the information of different function
required to transmit optical data through fiber optic cable.
• The OMS layer is used to manage the fiber connections
between optical multiplexer and switches.
• Optical channel layer is used to transmit the information form
user.
• Optical channel transport unit layer adds the Forward Error
Connection (FEC) to the network element.
• The OUT layer is similar to the section layer of SONET/SDH.
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21. Reference
• Wikipedia
• https://search.yahoo.com/search?ei=utf-
8&fr=tightropetb&p=SONET+system+images&type=6240
3_102417
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