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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