16.711 lecture 8 optical fiber amplifier – noise and ber last lecture introduction to fiber...
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16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Last lecture
• Introduction to Fiber Optical Amplifier – types and applications• Erbium-doped fiber amplifier (EDFA)• External pumping and amplifier gain • Power-conversion efficiency and gain profile
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Today
• Amplifier Noise• OSNR and BER• System Applications
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Einstein’s A and B coefficients
,)(|221121212 dvvgNAhvNBNhvNBNdz
dNmNmm
m
,1)( dvvg is the distribution function.)(vg
,)( 2121 hvBvA is number of optical modes at v.)(v
,)()( 2212112 dvvghvNBhvNBNNdz
dNm
m
,)()( 2212112 dvdzvghvNBhvNBNNdN mm
,)()()( 1221
212
dvdzvgNNhvBNNNN
dN
m
m
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Noise Power
,12
2
NN
Nnsp
is the spontaneous factor.
,)0(
)(Ge
nN
nLN gL
spm
spm
,)()(
)(
1221
12
2
dvdzvgNNhvB
NNN
N
dN
m
m
,)()( 1221 dvdzvgNNhvBnN
dN
spm
m
,))((|)ln( 12210 dvLNNvhvgBnN Lspm
),1()0()( GnGNLN spmm
,)1( vhvGnP spASE
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Amplified spontaneous noise
Noise Power spectral density:
,)1()( hvnGvS sp
,1
12
N
NNnsp
Total ASE power:
,)1()( vhvnGvvSP spASE
Total power:
,, vSGPPPP ASEinsASEsignal
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Receiver noise
Total photo-detector current:
,)( 2nstotal EEi
Total ASE power:
,42
R
kTT R is the resistance of the detector load resistor.
,, vSGPPPP ASEinsASEsignal
,222222, ASEASEASESASEshortSshortTnoisetotali
),1(42 GGnP spinASES
,2 02 BGPe inSshort
,)1(212
,
Gn
G
eB
P
N
S
sp
ins
out ,2
,
eB
P
N
S ins
in
,2)1(21
)/(
)/(sp
sp
in
in nG
Gn
NS
NSNF
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Receiver noise
Total photo-detector current:
,222222, ASEASEASESASEshortSshortTnoisetotali
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Gain and Noise Figure
Total photo-detector current:
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Amplifier System Noise figure (NF)
),()()( dBLossdBNFdBNF inputOAPtotal
Detector
EDF
Input
Output
ElectronicsExternal control
980 pump
WDM5%Tap
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
BER calculation:
,)0( hv
Es
eP
Quantum limit detection, Poisson’s equation:
,20hvEs ,101 9BER
,114
22/1
2/1
0
opt
opt
e SNR
SNR
B
BQ
Gaussian Noise Statistics :
,)
2exp(
2
1
2
Q
Q
BER
,)0()1(
2
)0()1(,
totaltotal
avgs
totaltotal
s
NN
I
NN
IQ
sp
avgSopt I
ISNR ,
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
BER calculation:
OSNR v.s. BER
1E-15
1E-14
1E-13
1E-12
1E-11
1E-10
8 9 10 11 12 13 14 15 16 17
OSNR (dB)
BE
R
Be = 1.7GHz
Be = 7GHz
• OSNR =10dB for 2.5GBit/s • OSNR =15dB for 10GBit/s
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
PreAmp:
,2
2
es
sin BeI
ISNR
,)( 2
TASEASEASES
sout NNN
GISNR
),1(4 GGnBeIN spesASES
,)1()2(2 220
2 GnBBBeN speeASEASE
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
In-line Amp:
,2
2
es
sin BeI
ISNR
,)( 2
TASEASEASES
sout NNN
GISNR
),1(4 GGnBeIN spesASES
,)1(4)1(4
)( 2
GnhvB
GP
GneB
GI
N
GISNR
spe
in
spe
s
ASES
sout
),1(2
2
)1(4 2
GG
n
BeI
I
GI
GneBNF sp
es
s
s
spe
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Amplifier Chain:
,2
2
es
sin BeI
ISNR ),1(4 GGnBeINN spesASES
,)1(4)1(4
)( 2
GNnhvB
P
GneBN
GI
NN
GISNR
spe
in
spe
s
ASES
sout
),1(2
2
)1(4 2
GG
Nn
BeI
NI
GI
GneBNF sp
es
s
s
spe
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Amplifier Chain:
,)1(4)1(4
)( 2
GNnhvB
P
GneBN
GI
NN
GISNR
spe
in
spe
s
ASES
sout
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Amplifier Chain:
,)1(4)1(4
)( 2
GNnhvB
P
GneBN
GI
NN
GISNR
spe
in
spe
s
ASES
sout
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Amplifier Chain:
0
5
10
15
20
25
30
35
0 5 10 15 20 25
Number of Amplifier
OS
NR
(d
B)
NF =8.5dB
NF=7dB
NF=9.5dB
16.711 Lecture 8 Optical Fiber Amplifier – noise and BER
Amplifier Chain:
OSNR of cascaded LOAs, G =18dB, NF=8.5dB, Pin=-21dBm
15
20
25
30
35
40
45
50
55
60
0 2 4 6 8 10number of LOA
OS
NR
(d
B)
simulation
measured