1 fiber optic communications systems from the movie warriors of the net optical time division...
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Fiber Optic Communications Systems
From the movieWarriors of the Net
Optical Time Division Multiplexing
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Multiplexing
• Frequency-division multiplexing (FDM) for electrical signals
• Code-division multiplexing (CDM) for electrical signals
• Wavelength-division multiplexing (WDM) for optical signals
• Time-division multiplexing (TDM) for both types
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Modulation
• Amplitude modulation
• Frequency modulation
• Phase modulation
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Simple to implement
• amplitude modulation
• pulse amplitude modulation
• amplitude shift keying
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Economize bandwidth
• quadrature amplitude modulation
• single sideband modulation
• vestigial sideband modulation
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Noise resistant
• phase modulation
• frequency modulation
• pulse position modulation
• pulse code modulation (widely used)
• amplitude shift keying
• frequency shift keying
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OTDM Bit Interleaved Multiplexer
Wavelength Division Multiplexing (WDM)
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Overview
• Wave Division Mutiplexing (WDM) multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. – Bit rate and protocol independent
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Overview
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Single Pair of Fibers
Single Pair of Fibers
Single Pair of Fibers
Single Pair of Fibers
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
Digital Transceiver
WDM MUX WDM MUX
Single Pair of Fibers
Traditional Digital Fiber Optic Transport
Digital Fiber Optic Transport using WDM
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Overview
• Two main types of WDM:– Coarse Wavelength Division Multiplexing (CWDM)– Dense Wavelength Division Multiplexing (DWDM)
Feature CWDM DWDM
Wavelengths per fiber 8 – 16 40 – 80
Wavelength spacing 2500GHz (20nm) 100 GHz (0.8nm)
Wavelength capacity Up to 2.5 Gbps Up to 10 Gbps
Aggregate fiber capacity 20 – 40 Gbps 100 – 1000 Gbps
Overall cost Low Medium
Applications Enterprise, metro-access Access, metro-core, regional
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Overview
• Fiber Characteristics
1550Window
1310Window
O - band E - band S - band C - band L - band
1280 1320 1360 1400 1440 1480 1520 1560 16001552Wavelength
(nm) CWDM Window
DWDM Window
C Band Range : 1530nm – 1560nmL Band Range : 1570nm – 1600nm
Water Peak
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OverviewWDM Components
Optical Multiplexer
Optical De-multiplexer
Optical Add/Drop Multiplexer(OADM)
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1...n
1...n
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Multiplexer Demultiplexer
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Add/DropMultiplexer
λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8 λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8
Transmission Fiber
WDM Block Diagram
Transmitters Receivers
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Components: Transmitters
• Each transmitter emits a signal at different wavelengths
• Laser source
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Components: Multiplexer
• All different signals from transmitters are combined into one signal
• The signal consists of several wavelengths, each containing a different signal
• Gratings, prisms and thin films
Multiplexerλ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8
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Gratings
• Simultaneously diffract all wavelengths
• Simple device
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Classical Grating
• Reflects light at an angle related to its wavelength
• Diffraction angle is dependent on the groove spacing and incident angle
Reflective Grating
λ1+λ2
λ1
λ2
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Components: Add/Drop Multiplexer
• Signal at specific wavelength can be extracted• Different signal at same wavelength can then be inserted• Fiber Bragg Grating
Add/DropMultiplexer
Transmission Fiber
λ4
λ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8 λ1 λ2 λ3 λ4’ λ5 λ6 λ7 λ8
λ4’
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Components: Demultiplexer
• Decouples different wavelengths to get different signals
Demultiplexerλ1 λ2 λ3 λ4 λ5 λ6 λ7 λ8
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Components: Receivers
• Optical detector• Receives a specific signal at a
specific wavelength
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OverviewSub-Lambda Multiplexing
• Multiplexing a single low rate data connection onto a wavelength is very inefficient.– For example, if a FastEthernet connection is transported on a
WDM wavelength, only 4% of the bandwidth is used. This assumes the wavelength is capable of transporting 2.5 Gbps.
• To better utilize bandwidth many vendors support sub-lambda multiplexing. – The cards that support this are often referred to as DataMux or
Muxponder cards.– Muxponder cards have multiple ports (FE, GE, etc.). These
cards multiplex the data flows and transports them onto a wavelength.
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Benefits of WDM
• WDM technology allows multiple connections over one fiber thus reducing fiber plant requirement. – This is mainly beneficial for long-haul applications.– Campus applications require a cost benefit analysis.
• WDM technology can also provide fiber redundancy.
• WDM provides a managed fiber service.