Wdm

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••WDMWDM

:: BASIC OPTICAL FIBER COMMUNICATION SYSTEM ::

••WDMWDM LightLight isis usedused asas carriercarrier.. FiberFiber isis usedused asas channelchannel..

Need of Multiplexing

For optimum utilization of fiber capacity.

To accommodate more datachannels/users.

Hence Multiplexing is to increase thebandwidth/ to exploit the capacity of anoptical channel.

For optimum utilization of fiber capacity.

To accommodate more datachannels/users.

Hence Multiplexing is to increase thebandwidth/ to exploit the capacity of anoptical channel.

Types of Multiplexing

Optical Time Division Multiplexing(OTDM)

Wavelength Division MultiplexingWavelength Division Multiplexing

:: WDM System & Components ::

ToTo ExploitExploit thethe totaltotal capacitycapacity ofof FiberFiber..

• Capacity upgrade of existing fibernetworks (without adding fibers).

• Transparency: Each optical channel cancarry any transmission format (differentasynchronous bit rates, analog or digital).

• Scalability– Buy and install equipment foradditional demand as needed.

• Wavelength routing and switching:Wavelength is used as another dimensionto time and space.

KEY FEATURES OF WDM

• Capacity upgrade of existing fibernetworks (without adding fibers).

• Transparency: Each optical channel cancarry any transmission format (differentasynchronous bit rates, analog or digital).

• Scalability– Buy and install equipment foradditional demand as needed.

• Wavelength routing and switching:Wavelength is used as another dimensionto time and space.

Fiber For WDM• Multimode Fiber: There are several electro-

magnetic modes that are stable within the fiber,Ex: TE01, TM01 .

• The injected power from the source is distributedacross all these modes .

• WDM is not possible with multimode fibers.• Single Mode Fiber: Only the fundamental mode

will exist.• All the coupled energy will be in this mode.• This mode occupies a very narrow spectrum –

making Wavelength Division Multiplexing possible

• Multimode Fiber: There are several electro-magnetic modes that are stable within the fiber,Ex: TE01, TM01 .

• The injected power from the source is distributedacross all these modes .

• WDM is not possible with multimode fibers.• Single Mode Fiber: Only the fundamental mode

will exist.• All the coupled energy will be in this mode.• This mode occupies a very narrow spectrum –

making Wavelength Division Multiplexing possible

WDM, CWDM and DWDM

• Early WDM systems transported two or fourwavelengths that were widely spaced.

• WDM and the follow on technologies of CWDMand DWDM have evolved well beyond this earlylimitation.

Wavelength Division Multiplexing (WDM):

• A simple WDM system uses two wavelengths oftwo different transmission windows, i.e. 1310 nmand 1550 nm.

WDM, CWDM and DWDM

• Early WDM systems transported two or fourwavelengths that were widely spaced.

• WDM and the follow on technologies of CWDMand DWDM have evolved well beyond this earlylimitation.

Wavelength Division Multiplexing (WDM):

• A simple WDM system uses two wavelengths oftwo different transmission windows, i.e. 1310 nmand 1550 nm.

Coarse WDM:

• Coarse WDM (CWDM) typically uses 20-nm spacing (3000GHz) of up to 18 channels.

• The CWDM grid is made up of 18 wavelengths definedwithin the range 1270 nm to 1610 nm spaced by 20 nm.

Dense WDM:

• Recent advances in DWDM technologies have significantlyincreased achievable capacities and distances for opticaltransmission systems.

• Dense WDM common spacing may be 200, 100, 50, or 25GHz with channel count reaching up to 128 or morechannels at distances of several thousand kilometers withamplification and regeneration along such a route.

Coarse WDM:

• Coarse WDM (CWDM) typically uses 20-nm spacing (3000GHz) of up to 18 channels.

• The CWDM grid is made up of 18 wavelengths definedwithin the range 1270 nm to 1610 nm spaced by 20 nm.

Dense WDM:

• Recent advances in DWDM technologies have significantlyincreased achievable capacities and distances for opticaltransmission systems.

• Dense WDM common spacing may be 200, 100, 50, or 25GHz with channel count reaching up to 128 or morechannels at distances of several thousand kilometers withamplification and regeneration along such a route.

Types of WDM SystemCWDM & DWDM

The fundamental difference between CWDM and DWDM isone of only degree. DWDM spaces the wavelengths moreclosely than CWDM, and therefore has a greater overall

capacity .

• The difference between WDM, CWDM and DWDM isfundamentally one of only degree.

• DWDM spaces the wavelengths more closely than doesWDM, and therefore has a greater overall capacity.

• WDM, CWDM and DWDM use single-mode fiber tocarry multiple light waves of differing frequencies.

WDM, CWDM and DWDM• WDM technology uses multiple wavelengths

to transmit information over a single fiber.• Coarse WDM (CWDM) has wider channel

spacing (20 nm) – low cost.• Dense WDM (DWDM) has dense channel

spacing (0.8 nm) which allows simultaneoustransmission of 16+ wavelengths – highcapacity.

• WDM technology uses multiple wavelengthsto transmit information over a single fiber.

• Coarse WDM (CWDM) has wider channelspacing (20 nm) – low cost.

• Dense WDM (DWDM) has dense channelspacing (0.8 nm) which allows simultaneoustransmission of 16+ wavelengths – highcapacity.

ITU-T Standard Transmission DWDMwindows

Principles of DWDM• BW of a modulated laser: 0.001 nm• Typical Guard band: 0.4 – 1.6 nm• 80 nm or 14 THz @1300 nm band• 120 nm or 15 THz @ 1550 nm• Discrete wavelengths form individual channels that

can be modulated, routed and switchedindividually.

• These operations require variety of passive andactive devices.

• BW of a modulated laser: 0.001 nm• Typical Guard band: 0.4 – 1.6 nm• 80 nm or 14 THz @1300 nm band• 120 nm or 15 THz @ 1550 nm• Discrete wavelengths form individual channels that

can be modulated, routed and switchedindividually.

• These operations require variety of passive andactive devices.

Nortel OPTERA 640 System

•64 wavelengths each carrying 10 Gb/s

WDM SYSTEM PERFORMS THEFOLLOWING MAIN FUNCTIONS:

Generating the signal The source, a solid-state laser, must provide stable light within a

specific, narrow bandwidth that carries the digital data, modulatedas an analog signal.

Combining the signals Modern WDM/DWDM systems employ multiplexers to combine

the signals. There is some inherent loss associated with multiplexing and

demultiplexing. This loss is dependent upon the number of channels but can

be mitigated with optical amplifiers, which boost all thewavelengths at once without electrical conversion.

Generating the signal The source, a solid-state laser, must provide stable light within a

specific, narrow bandwidth that carries the digital data, modulatedas an analog signal.

Combining the signals Modern WDM/DWDM systems employ multiplexers to combine

the signals. There is some inherent loss associated with multiplexing and

demultiplexing. This loss is dependent upon the number of channels but can

be mitigated with optical amplifiers, which boost all thewavelengths at once without electrical conversion.

Transmitting the signals The effects of crosstalk and optical signal degradation or loss

must be reckoned (consideration) with fiber optic transmission. These effects can be minimized by controlling variables such as

channel spacing's, wavelength tolerance, and laser power levels.Over a transmission link, the signal may need to be opticallyamplified.

Separating the received 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, it is actually more technically difficult. Receiving the signals

The demultiplexed signal is received by a photodetector.

WDM SYSTEM PERFORMS THEFOLLOWING MAIN FUNCTIONS:

Transmitting the signals The effects of crosstalk and optical signal degradation or loss

must be reckoned (consideration) with fiber optic transmission. These effects can be minimized by controlling variables such as

channel spacing's, wavelength tolerance, and laser power levels.Over a transmission link, the signal may need to be opticallyamplified.

Separating the received 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, it is actually more technically difficult. Receiving the signals

The demultiplexed signal is received by a photodetector.

:: WDM COMPONENTS ::

Key components for WDMPassive Optical Components• Wavelength Selective Splitters• Wavelength Selective Couplers• Wavelength Selective Circulators• Wavelength Selective IsolatorsActive Optical Components• Tunable Optical Filter• Light Source & Detectors• Optical amplifier• Add-drop Multiplexer and De-multiplexer

Passive Optical Components• Wavelength Selective Splitters• Wavelength Selective Couplers• Wavelength Selective Circulators• Wavelength Selective IsolatorsActive Optical Components• Tunable Optical Filter• Light Source & Detectors• Optical amplifier• Add-drop Multiplexer and De-multiplexer

Light Sources for WDM

• Lasers needed for WDM systems are almost same aslasers for ordinary long distance communication.

• However, some requirements are more critical withWDM and a number of new requirements becomeapparent.

Spectral Width and Linewidth

• In general in a dense WDM system we need a laser withonly one line in its spectrum.

• This will mean either a DFB or a DBR laser.

• In general the narrower the linewidth, the betterperformance, but this will usually be a cost/benefittradeoff.

• Lasers needed for WDM systems are almost same aslasers for ordinary long distance communication.

• However, some requirements are more critical withWDM and a number of new requirements becomeapparent.

Spectral Width and Linewidth

• In general in a dense WDM system we need a laser withonly one line in its spectrum.

• This will mean either a DFB or a DBR laser.

• In general the narrower the linewidth, the betterperformance, but this will usually be a cost/benefittradeoff.

Wavelength Stability• In most long-distance (single channel) systems

we need very stable, narrow linewidth lasers tominimize the effects of dispersion and things likemode partition noise.

• However, in a WDM system we need tominimize the change in wavelength over time.

• A shift of a nm or two taking place over a fewseconds might not bother a regular WAN singlechannel system but it would disrupt a WDM one.

Wavelength Stability• In most long-distance (single channel) systems

we need very stable, narrow linewidth lasers tominimize the effects of dispersion and things likemode partition noise.

• However, in a WDM system we need tominimize the change in wavelength over time.

• A shift of a nm or two taking place over a fewseconds might not bother a regular WAN singlechannel system but it would disrupt a WDM one.

Optical Couplers & Splitters• Couplers are the simplest optical devices.

• They are passive and completelybidirectional in nature in the sense that wecan interchange the input and output ports.

• Couplers are N x M, where N and M areintegers.

• In other words, we can have N inputsegments (fibers) and M output segments(fibers).

• Couplers are the simplest optical devices.

• They are passive and completelybidirectional in nature in the sense that wecan interchange the input and output ports.

• Couplers are N x M, where N and M areintegers.

• In other words, we can have N inputsegments (fibers) and M output segments(fibers).

• The principle is to fuse the cores of the N inputfibers to the cores of M output fibers so as tocreate a power transfer device.

• Practically, 2 x 2 couplers are most commonand are known as 3dB couplers because of the 3dB loss in power at each output port due to asignal at one of the input ports.

• Couplers find applications for monitoring WDMports as well as for passively adding channelsinto a fiber.

• They are also used in passive optical networks(PONs).

• The principle is to fuse the cores of the N inputfibers to the cores of M output fibers so as tocreate a power transfer device.

• Practically, 2 x 2 couplers are most commonand are known as 3dB couplers because of the 3dB loss in power at each output port due to asignal at one of the input ports.

• Couplers find applications for monitoring WDMports as well as for passively adding channelsinto a fiber.

• They are also used in passive optical networks(PONs).

Circulators• A circulator is a multiport device that

allows signals to propagate in certaindirections based on the port that the signalcame from (incident port).

• In Figure, the signal from port 1 movesfreely to port 2; while the signal from port2 cannot go to port 1, but it can go to port3.

• Likewise, the signal from port 3 can go toport 1 but not to port 2.

• A circulator is a multiport device thatallows signals to propagate in certaindirections based on the port that the signalcame from (incident port).

• In Figure, the signal from port 1 movesfreely to port 2; while the signal from port2 cannot go to port 1, but it can go to port3.

• Likewise, the signal from port 3 can go toport 1 but not to port 2.

• The operation is analogous to an optical valve,which allows unidirectional propagation only.

Isolators• An isolator is a device that allows light to pass

along a fiber in one direction but not in theopposite direction.

• Operation of laser diodes (LD) and opticalamplifiers (EDFA) become unstable andgenerate noise when returned light enters.

• Optical isolator utilize Faraday effect to cut offthe returned beam and stabilize the operation oflasers and amplifiers.

• An isolator is a device that allows light to passalong a fiber in one direction but not in theopposite direction.

• Operation of laser diodes (LD) and opticalamplifiers (EDFA) become unstable andgenerate noise when returned light enters.

• Optical isolator utilize Faraday effect to cut offthe returned beam and stabilize the operation oflasers and amplifiers.

• However, one optical phenomenon is not bi-directional.

• This is the “Faraday Effect”.

• This effect is polarization dependent so in orderto use it one has to take account of polarization.

Dielectric Thin-Film Filters• A dielectric thin-film filter (TFF) is used as an

optical band pass filter.

• This means that it allows a particular, verynarrow wavelength band to pass straight throughit and reflects all others.

• The basis of these devices is a classical Fabry-Perot filter structure, which is a cavity formed bytwo parallel, highly reflective mirror surfaces.

• This structure is called a Fabry-Perotinterferometer or an etalon or thin-film resonantcavity filter.

• A dielectric thin-film filter (TFF) is used as anoptical band pass filter.

• This means that it allows a particular, verynarrow wavelength band to pass straight throughit and reflects all others.

• The basis of these devices is a classical Fabry-Perot filter structure, which is a cavity formed bytwo parallel, highly reflective mirror surfaces.

• This structure is called a Fabry-Perotinterferometer or an etalon or thin-film resonantcavity filter.

• A Fabry Perot cavity consists of two reflectivesurfaces that are separated by a hollow region.

• The distance between the reflective surfaces canbe made to change by changing the currentassociated with the transducer, responsible forcreating the cavity.

• A Fabry Perot cavity consists of two reflectivesurfaces that are separated by a hollow region.

• The distance between the reflective surfaces canbe made to change by changing the currentassociated with the transducer, responsible forcreating the cavity.

• The reflective surfaces are with reflectivity, thatis a function of the operating wavelength.

• The reflectivity can be made to change fordifferent resonant wavelengths.

• For a resonating cavity, the resonant wavelengthis the only wavelength, and it does not sufferreflection from one of the two mirrored walls.

• The reflective surfaces are with reflectivity, thatis a function of the operating wavelength.

• The reflectivity can be made to change fordifferent resonant wavelengths.

• For a resonating cavity, the resonant wavelengthis the only wavelength, and it does not sufferreflection from one of the two mirrored walls.

•DWDM

••:: MODULATORS :::: MODULATORS ::

The process of imposing data on light stream is calledModulation.

Laser is directlymodulated with data.

•DWDM

Modulation takes place inexternal cavity.

Periodic LASER source isused.

Increases extinction ratioo.

•DWDM

••:: MZM EXTERNAL MODULATOR :::: MZM EXTERNAL MODULATOR ::

•DWDM

Works based on interference of light by changing phase .

Use of electro-optic effect, where an applied voltage inducesa change in refractive index of the material.

OpticalMultiplexer/De-Multiplexer

•Optical Multiplexers receive several spatiallyseparated wavelengths and form a single beam thatconsists of all these wavelengths.•De-Multiplexers perform the reverse functionalityof multiplexers; they receive a multi-wavelengthbeam and separate it spatially into its wavelengthcomponents; that is, each wavelength appears at adifferent output.

••Different MUXDifferent MUX--DEMUX TechnologiesDEMUX Technologies

•• AArrayedrrayed WWaveguideaveguide GGrating:rating: AWGAWG•• FFiberiber BBraggragg GGrating:rating: FBGFBG•• TThinhin FFilmilm FFilters:ilters: TFFTFF•• DDiffractioniffraction GGrating:rating: DGDG

•DWDM

Mach-Zehnder Interferometer (MZI)

•DWDM

Works based on Interference principle.

Two propagating signals can be made to obtain different phaseshifts by varying the lengths of the two arms.

The signals, upon interfering with each other at coupler B,might have constructive or destructive interference.

•Diffraction Grating

•Multiplexer

••WDMWDM

•Diffraction Grating

•(De) Multiplexer

••FBGFBG ••MZI with FBG MultiplexerMZI with FBG Multiplexer

••MZI with FBG DeMultiplexerMZI with FBG DeMultiplexer

•• DeMUXDeMUX•• MUXMUX

Circulator with FBG (De)MultiplexerCirculator with FBG (De)Multiplexer

Optical Add-Drop Multiplexor (OADM)

•OADM

•’3•’3

•’3•3

•DWDM

:::: Arrayed Waveguide Grating (AWG) ::::

•DWDM

Works based on Interference and Grating principle.

An AWG device consists of many waveguides of differentlengths converging at the same point (s).

Signals coming through each of these waveguides travelthrough a length such that they interfere from the signalsthrough the other waveguides (at the converging point) eitherconstructively or destructively.

TFFTFF

Thin Film Filter (De)MultiplexerThin Film Filter (De)Multiplexer

Optical Switch• 1-input 2-outoput illustration with four

wavelengths

• 1-D MEMS (micro-electromechanical system) withdispersive optics– Dispersive element separates the ’s from inputs– MEMS independently switches each – Dispersive element recombines the switched ’s

into outputs

•1-D MEMS•Micro-mirror

•Digital MirrorControl

Electronics•1011

•WavelengthDispersive Element

•Input Fiber

•Output Fiber 1•

Output Fiber 2

•Input & Outputfiber array

• 1-input 2-outoput illustration with fourwavelengths

• 1-D MEMS (micro-electromechanical system) withdispersive optics– Dispersive element separates the ’s from inputs– MEMS independently switches each – Dispersive element recombines the switched ’s

into outputs

•Input Fiber

•Output Fiber 1•

Output Fiber 2

All-Optical Switching• Optical Cross-Connects (OXC)

– Wavelength Routing Switches (WRS)

– route a channel from any I/P port to any O/P port

• Natively switch s while they are still multiplexed• Eliminate redundant optical-electronic-optical

conversions

• Optical Cross-Connects (OXC)

– Wavelength Routing Switches (WRS)

– route a channel from any I/P port to any O/P port

• Natively switch s while they are still multiplexed• Eliminate redundant optical-electronic-optical

conversions

•DWDM•Fibers

•DWDM•Demux

•DWDM•Fibers

•DWDM•Mux

•All-opticalOXC

Wavelength () Converters (WC) improve utilization of available wavelengths

on linksneeded at boundaries of different networksall-optical WCs being developedgreatly reduce blocking probabilities

•3 •3

improve utilization of available wavelengthson links

needed at boundaries of different networksall-optical WCs being developedgreatly reduce blocking probabilities

•No Wavelength converters

•2 •3

•New request• 1 3

•With Wavelength converters

•2 •3

•New request• 1 3

Optical systemsOptical systems

•Point To Point Systems

Network Systems

•Point to Multipoint•Ring•Mesh

••

Optical systemsOptical systems

•Point To Point Systems

Network Systems

•Point to Multipoint•Ring•Mesh

••

OPTICAL SYSTEM DESIGN CRITERIAOPTICAL SYSTEM DESIGN CRITERIA

••WDMWDM

•DWDM

••:: SYSTEM DESIGN CRITERIA :::: SYSTEM DESIGN CRITERIA ::

• It is not a small task to put the components together (e.g.fibers, connectors, lasers, detectors, etc.), so that the wholewill function as a communication system with desirablecharacteristics.

• Proper design/ engineering is requires for this task.

(1) Primary Design Criteria: Link Length Data Rate/BW

(2) Secondary Design Criteria: System Fidelity: BER, OSNR, Q-factor Cost: Components, installation, maintenance Upgradeability: Future Planning

•DWDM

• It is not a small task to put the components together (e.g.fibers, connectors, lasers, detectors, etc.), so that the wholewill function as a communication system with desirablecharacteristics.

• Proper design/ engineering is requires for this task.

(1) Primary Design Criteria: Link Length Data Rate/BW

(2) Secondary Design Criteria: System Fidelity: BER, OSNR, Q-factor Cost: Components, installation, maintenance Upgradeability: Future Planning

•DWDM

System Factor ConsiderationsType of Fiber Single-mode or MultimodeOperating Wavelength 780, 850, 1310 and 1550 nm

typicalTransmitter Power Typically expressed in dBmSource Type LED or LaserReceiver Sensitivity andOverloadCharacteristics

Typically expressed in dBm

Detector Type PIN Diode or APD

•Factors for Evaluating Fiber Optic System Design

•DWDM

System Factor ConsiderationsType of Fiber Single-mode or MultimodeOperating Wavelength 780, 850, 1310 and 1550 nm

typicalTransmitter Power Typically expressed in dBmSource Type LED or LaserReceiver Sensitivity andOverloadCharacteristics

Typically expressed in dBm

Detector Type PIN Diode or APD

•DWDM

System Factor ConsiderationsModulation Code AM, FM, PCM or DigitalBit Error Rate (BER)(Digital Systems Only)

10-9 ,10-12 Typical

Signal to Noise Ratio Specified in decibels (dB)Number of Connectors Loss increases with the number of

connectorsNumber of SplicesLoss is Loss increases with the number of

splicesEnvironmentalRequirements

Humidity, Temperature,Exposure to sunlight

Mechanical Requirements Flammability, Indoor/OutdoorApplication

•Factors for Evaluating Fiber Optic System Design

•DWDM

System Factor ConsiderationsModulation Code AM, FM, PCM or DigitalBit Error Rate (BER)(Digital Systems Only)

10-9 ,10-12 Typical

Signal to Noise Ratio Specified in decibels (dB)Number of Connectors Loss increases with the number of

connectorsNumber of SplicesLoss is Loss increases with the number of

splicesEnvironmentalRequirements

Humidity, Temperature,Exposure to sunlight

Mechanical Requirements Flammability, Indoor/OutdoorApplication

•DWDM

OPTICAL SYSTEM engineeringOPTICAL SYSTEM engineering•DWDM

•DWDM

••:: SYSTEM ENGINEERING :::: SYSTEM ENGINEERING ::

•DWDM

••:: SYSTEM ENGINEERING :::: SYSTEM ENGINEERING ::

•DWDM

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DISPERSION LIMITED LIGHTWAVE SYSTEMSDISPERSION LIMITED LIGHTWAVE SYSTEMS

22 2 216 8327 (Gbps) - kms

DB L B L

•So from above equations we can find

•If System Bit Rate = 2.5 Gbps L < 1332.32 kms•If System Bit Rate = 10 Gbps L < 83.27 kms•If System Bit Rate = 40 Gbps L < 5.204 Kms

We can conclude that as B increases, L decreases with the square root of B.

•So from above equations we can find

•If System Bit Rate = 2.5 Gbps L < 1332.32 kms•If System Bit Rate = 10 Gbps L < 83.27 kms•If System Bit Rate = 40 Gbps L < 5.204 Kms

We can conclude that as B increases, L decreases with the square root of B.

•DWDM

OPTICAL LINK DESIGNOPTICAL LINK DESIGN

1. Power Budget2. Bandwidth/Rise Time Budget

•DWDM

OPTICAL LINK DESIGNOPTICAL LINK DESIGN

1. Power Budget2. Bandwidth/Rise Time Budget

:: DWDM SYSTEM DESIGN :::: DWDM SYSTEM DESIGN ::

LOSS LIMITED LIGHTWAVE SYSTEMSLOSS LIMITED LIGHTWAVE SYSTEMS

( )M a x

i n rP PL

•Loss Compensation using Optical Amplifiers [1]

•Noise Accumulation Resulting from Multistage Amplification

•DWDM

DESIGN OF POINT-TO-POINT DWDM LINK BASED ON OSNR

• Consider a physical link AB, a long-haul fiber DWDM link(a link that is several hundred kilometers). , as shown inFigure.

• Amplifiers are placed periodically at repeated intervals toboost signal power.

• Therefore, a signal can reach much farther than themaximum allowable accumulated loss due to the fiber (L).•DWDM

• Consider a physical link AB, a long-haul fiber DWDM link(a link that is several hundred kilometers). , as shown inFigure.

• Amplifiers are placed periodically at repeated intervals toboost signal power.

• Therefore, a signal can reach much farther than themaximum allowable accumulated loss due to the fiber (L).

•DWDM

• Each amplifier stage adds its own component ofASE noise and degrades the OSNR further.

• Moreover, every amplifier amplifies the alreadypresent noise.

• This noise is present throughout the spectra andalmost impossible to be removed.

• It is imperative to devise a method to calculate theOSNR (output) at the end of an N stage-amplifiedsystem and see if the value N is still valid.

•DWDM

• Each amplifier stage adds its own component ofASE noise and degrades the OSNR further.

• Moreover, every amplifier amplifies the alreadypresent noise.

• This noise is present throughout the spectra andalmost impossible to be removed.

• It is imperative to devise a method to calculate theOSNR (output) at the end of an N stage-amplifiedsystem and see if the value N is still valid.

•DWDM

• In an OSNR-based design, we must ensure that OSNR ofthe final stage is in compliance with system OSNRrequirements and hence the BER requirements.

• To make the system support a particular BER, it is necessaryto make the OSNR system design compliant.

• The OSNR of each stage is given by,

• Where NFstage is the noise figure of the stage,

• h is Plank's constant (6.6260 x 10-34),

• v is the optical frequency (193 THz), and

• Δf is the optical bandwidth of the receiver (0.1 nm or 12.5GHz).

•DWDM

• In an OSNR-based design, we must ensure that OSNR ofthe final stage is in compliance with system OSNRrequirements and hence the BER requirements.

• To make the system support a particular BER, it is necessaryto make the OSNR system design compliant.

• The OSNR of each stage is given by,

• Where NFstage is the noise figure of the stage,

• h is Plank's constant (6.6260 x 10-34),

• v is the optical frequency (193 THz), and

• Δf is the optical bandwidth of the receiver (0.1 nm or 12.5GHz).

•DWDM

Remember:• In above equation of OSNR, Pin is in dBm.

:: DWDM SYSTEM DESIGN :::: DWDM SYSTEM DESIGN ::

DESIGN OF POINTDESIGN OF POINT--TOTO--POINT DWDM LINK BASED ON OSNRPOINT DWDM LINK BASED ON OSNR

Single Stage N StageOSNR OSNRin in

NF h f NF hv f N

OSNR (dB) 58 ( ) ( ) ( ) ( ) 10logindB P dBm db NF dB N

•DWDM

DISPERSION COMPENSATION IN WDM

•DWDM

DISPERSION COMPENSATION IN WDM

•DWDM

OSNR & DISPERSION BASED SYSTEM

•DWDM

WDM SYSTEM DESIGN EXAMPLES•DWDM

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EXAMPLES

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SOLUTION

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EXAMPLES

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SOLUTION

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EXAMPLES

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SOLUTION

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EXAMPLES

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SOLUTION

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EXAMPLES

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SOLUTION

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SOLUTION

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SOLUTION

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EXAMPLES

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EXERCISES•DWDM

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