1

Lecture 7bDWDM

1. Introduction

2. Principles of Wavelength Division Multiplexing

3. WDM System Components

4. Wavelength-Independent Coupler

5. Construction of Wavelength Independent Couplers

6. Wavelength-Dependent Coupler

(Multiplexer/Demultiplexer)

7. WDM Communication System

8. Dense Wavelength Division Multiplexing (DWDM)

9. Add-drop Multiplexer

10. Conclusion

11. Appendix

2

• Time Division Multiplexing (TDM)• Wavelength Division Multiplexing

(WDM) • TDM divides a high-bandwidth transmitted

signal into time slots. Each time slot carries a different low-bandwidth signal.

• In WDM, several high-bandwidth signals travel on the same fiber, in the same time, each using a different light wavelength.

• DWDM uses the same principles as a WDM, but with high density of light wavelength alocation.

• A common application of multiplexing is in long-distance data and voice communications.

3

Access techniques for mobile communications

P - PowerT - TimeF - Frequency

P

T

P

T

F

P

T

F

FDMA (TACS)

TDMA (GSM, DECT)

CDMA (UMTS)

F

ATDMA (UMTS)

4

Principles of Wavelength Division Multiplexing (WDM)

 

Transmitter Multiplexer

m1 (t)

Transmitter m2 (t)

Transmitter m3 (t)

Transmitter mn (t)

Demultiplexer

λ1

λ2

λ3

λn

λ1

λ2

λ3

λn

Receiver

Receiver

Receiver

Receiver

optic fiber

m1 (t)

m2 (t)

m3 (t)

mn (t)

5

WDM System Components

• A coupler combiner, and a splitter,

• Couplers are bi-directional devices;

Wavelength Independent

Wavelength Dependent

6

Wavelength-Independent Coupler

 

1

2

3

3

110

1

310 log10

input)(

output)unwanted(log10loss

P

P

P

PD

2

110log10loss

P

PTHROUGHPUT

2

310log10loss

P

PTAP

2

3110log10loss

P

PPEXCESS

3

1ratioSplittingP

P

7

Input power = 1 mWSplitting ratio of each coupler = 9:1 Excess loss of each coupler = 0.3 dB

Insertion loss of each connector = 0.2 dB

 

1

2 3

1

2 3

1

2 3

Terminal 1 Terminal 2 Terminal 3

The input power is 1 mW, so we can express the power as zero decibel milliwatts(0 dBm). The incoming power level to first splitter is reduced by 0.2 dB by the first connector, and 0.3 dB by the excess loss. At the first splitter, we have total power of -0.5 dBm, or:

W3.89110mW1poweTotal dBm)5.0(1.0 r

8

Construction of a Wavelength Independent Coupler

Fused area

fibers

In the fused area, some light is able to enter the other fiber.

(throughput) Port 1

Port 3 (tap)

(input) Port 2

The screw adjuster movesthe input fiber to vary thesplitting ratio

Light entersboth fibers

Port 1light input

Port 2output

Port 3output

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Wavelength-Dependent Couplers (Multiplexer / Demultiplexer)

max

min

min

max

max

P (Bright area)

R (Dark area)

(a) Constructive Interference (waves combine at point P)

(b) Destructive Interference (waves are opposite in magnitude at point R)

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Input fiber

P

d

d θ

λ = d sin( θ )

θ

λ

A

B

Output fiber

Q

...),3,2,1,0()sin( mmd (8.5)

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Input fiber

P1

d

d

θ1

λ2 = d sin( θ2 )

λ1 , λ2

A

B

Fiber 1

P2 Fiber 2

λ1

λ2

θ2

λ1 = d sin( θ1 )

Q

...),3,2,1,0()sin( mmd

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WDM Communication System

Optical fiber

Transmitter 1 λ1 = 850 nm

λ1 , λ2

Receiver 1 λ1 = 850 nm

Transmitter 2 λ2 = 1300 nm

Receiver 2 λ2 = 1300 nm

λ1 , λ2

Multiplexer Demultiplexer

λ1

λ2

λ1

λ2 (8.6)

 

portcombined,innm1300

portnm850,outnm130010nm1300

portcombined,innm850

portnm1300,outnm85010nm850

log10CrT

log10CrT

P

P

P

P

CCCC nmnmeff 21300850

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optic fiber

1 = 1530.3 nm 2 = 1531.9 nm

λ3 = 1533.5 nm

λ4 = 1535.0 nm

λ20 = 1560.6 nm

λpump = 980 nm

doped fiber

λ1 = 1530.3 nm

λ2 = 1531.9 nm

λ3 = 1533.5 nm

λ4 = 1535.0 nm

λ20 = 1560.6 nm

optic fiber

EDFA

Multiplexer Demultiplexer

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• Several modulated laser sources, one for each optical channel.

• A Distributed Feedback (DFB) laser is the best source for a DWDM system, narrow bandwidth, (less than 0.4 nm). Modulation

• Erbium Doped Fiber Amplifier (EDFA), An optical demultiplexer to separate each signal at its destination.

• Suitable detectors for each signal to extract the information in that.

• A DWDM system can be designed with 41 channels in the range of 1528 nm to 1561 nm. DWDM can increase the capacity of a single fiber to as much as several hundred gigabits per second. This is the same capacity as several thousand 100Base-T Ethernet cables.

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StimulatedEmission1520-1620 nm

-1 mks

Short-wavelengthSource (980 nm)

Longer-wavelengthSource (1480 nm)

Excited erbium atoms at high energy level

Atoms at metastable energy (-10 ms)

Erbium atoms at low energy level