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Optical AmplifiersAn Important Element of

WDM Systems

Xavier FernandoADROIT Group

Ryerson University

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Nortel OPTERA System

64 wavelengths each carrying 10 !"s

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Optical Amplifiers

Conventional Repeaters in N-WDMsystems are very inefficient: Wavelength de-multiplexing

!" conversionelectrical amplification retimingpulse shaping"!conversion#

$avelength multiplexing

ptical %mplifiers:% single device thatamplify multiple format signals that arecarried &y multiple $avelengths

N -times

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#asic $oncepts

Most optical amplifiers use stimulated emission An optical amplifier is basically a laser without

feedback

ptical !ain is reali"ed when the amplifier is pumpedoptically #or electrically$ to achie%epopulation

inversion

&ain depends on wa%elen!th' internal li!ht intensity

and amplifier medium (wo types) semiconductoroptical amplifiers and

fiber dopedamplifiers

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Applications

*ower Amp

+onfi!urations

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Similar to ,aser diodes but the emission is tri!!ered

by input optical si!nal

Work in any wa%elen!th #$

.a%e hi!h inte!ration' compact and low power

consumption #$

&ain fluctuation with si!nal bit rate #-$

+ross talk between different wa%elen!ths #-$

(wo types) /abry-*erot or (ra%elin! Wa%e Amp0

Semicon%&ctor Optical Amplifiers

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eneric optical amplifier

+ontinuous Wa%e

#+onstant$

Ener!y is transferred from the pump to si!nal

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Soli% State Amplifier ain vers&s Power

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'istri!&te% (i!er Amplifiers

(he acti%e medium is created by li!htlydopin! silica fiber core by rare earth elementE1) Erbium #Er$

,on! fiber len!th #23-43 m$ ,ow couplin! loss #$

(ransparent to si!nal format and bit rate

No cross talk 5road output spectrum #2643 7 2683 nm$

)or*s only in specific )avelengths

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'())* nm

+,* nm

RadiationlessDecay

'())* nm

ump

.ignal

utput

Optical Pumping to Higher Energy levels Rapid Relaxation to "metastable" State

Stimulated Emission and Amplification

N(

N/

N0

N(

N/

N0

N(

N/

N0

Amplification *rocess of ED/A

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/i!0 22-9) Erbium ener!y-le%el dia!ram

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ED/Aconfi!urations

+o-Directional *umpin!

+ounter Directional

Dual *umpin!

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&ain %ersus ED/A len!th

(here is an

optimum len!th

that !i%es the

hi!hest !ain

Ne!ati%e !ain if

too lon!

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&ain %ersus pump le%el

&ain decreases at

lar!e si!nal

le%els

Si!nal dependant

!ain

(his increaseswith the pump

power

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Amplified Spontaneous Emission #ASE$ Noise

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ED/A Noise /i!ure

: #Input SN;$

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SN; de!radation due to amplification

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(ig+ 11,1-a. ain,flattene% E'(A,A

Research Topic. /ne&al gain across the spectr&m+

ow %o we flatten the gain 2

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(ig+ 11,1-!. ain,flattene% E'(A,#

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(ig+ 11,13. Passive gain control

Operating the '(A in the gain sat&ration region

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(ig+ 11,14. )avelength conversion