Post on 07-Jul-2020
02/14/06 EE233. Prof. Kaminow 1
EE 233. LIGHTWAVE
SYSTEMS
Chapter 4. Optical
Receivers
Instructor:
Ivan P. Kaminow
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PHOTODIODES
•PIN
•APD
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Ip = RPin, R = responsivity (A/W)
[square-law detector]
! = electrons out/photons in
= (Ip/q)/(Pin/h") = (h"/q)R
R = !q/h" = !#/1.24
1.24 = hc/q (µm/V)
$f = [2%(&tr + &RC]-1,
'tr = transit time ~ W/vd ~ 100 ps,
&RC = ckt response
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depletion
depletion
R ~ 1 A/W
!
"
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Intrinsic,
hi res
Also DH structure
(also waveguided)
! ~ 1,
W ~ 5µm
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RECEIVER NOISE
•Shot noise
•Thermal noise
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Example of Typical Link Experiment
Eye
diagram
-35 -30 -25 -20
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8
1E-9
Bit E
rror
Ratio
Received Optical Power (dBm)
Some
distance
of fiber
Back to
back
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SHOT NOISE
•I(t) = Ip + is(t)
•White noise
• (s2 = <is
2(t)> = 2qIp$f
•Ip -> Ip + Id
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Yariv
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THERMAL NOISE
•I(t) = Ip + Is(t) + IT(t)
• (T2 = <iT
2(t)> = (4kBT/RL)$f
•White noise
• (T2 = (4kBT/RL)Fn$f
•Fn = (S/N)in/ (S/N)out
= Amplifier noise figure
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SIGNAL TO NOISE RATIO
•SNR = avg signal pwr/noise pwr
= Ip2/(2
•Ip = RPin , R = !q/h"
• (2 = (s2 + (T
2, (T2>> (s
2 in practice
•(SNR)T = RLR2Pin2/4kBTFn$f
•NEP = Pin/($f)1/2 = (4kBTFn/RLR2)1/2,
SNR = 1
•(SNR)s = RPin/2q $f
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Yariv
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BIT ERROR RATE
•BER = (1/2)[P(0/1) + P(0/1)]
•min BER for
(ID - I0)/(0 = (I1- ID)/(1 = Q
•ID = ((0 I1 + (1 I0)/ ((0 + (1)
•Q = (I1 - I0)/((1 + (0)
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YARIV
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Transmission Performance
• Bit Error Rate (BER) vs. Min. Ave. Received
Power
Optimal
decision level 10
0110
!!
!!
+
+=
IIIth
01
01
22
1
!! +
"=
##$
%&&'
(=
IIQ
QerfcBER
2
2
0
2
1
012Q
PPSNR !
+
"=
##
( )
!2
2/2
Q
eBER
Q"
#
= Optical SNR
Q=6 ! BER=1e-9; Q=7 ! BER=1e-12
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MINIMUM REC’D PWR
•(Prec)pin~ Q(T/R
(T2 = (4kBT/RL)$f
$f ~ B/2
Q ~ 6 for 10-9 BER
•Prec ~ 0.6 µW or -32.2 dBm for
# = 1550nm, R = 1 A/W,
(T ~ 100nA, B ~ 10 Gb/s
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QUANTUM LIMIT
•quantum limit is <Np> =10 photons/bit,
with (0 = 0 and BER < 10-9
• Prec = <Np> h"B
= 13 nW or -48.9 dBm atB = 10 Gb/s
•In practice, Prec is 20 dB larger,corresponding to 1000 photons/bit
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POWER PENALTY
•Increases Prec
•Transmission impairments•Chromatic dispersion•PMD•SPM, XPM•FWM
•Receiver impairments•Extinction ratio P0/P1
•RIN•Timing jitter
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Desurvire
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AGRAWAL(2005)-systems
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Performance Impairment• Power penalty is
typically due to
– Mode partition noise
– Dispersion
– Chirp
– Noise
– Jitter
– Extinction ratio
– Etc.-35 -30 -25 -20
1E-3
1E-4
1E-5
1E-6
1E-7
1E-8
1E-9
Bit E
rror
Ratio
Received Optical Power (dBm)
Some
distance of
fiber
Back to back Power
Penalty
Example of a closed eye
Forward Error Correcting Codes in
Fiber Optic Systems
Mux FEC EncoderFEC Encoder TransTransmission
LineDemuxFEC DecoderFEC DecoderRcv
Transmit Terminal Receive Terminal
6 7 8 9 10 11 12
10--11
10--7
10--3
2.7e-002 2.7e-003 3.6e-005
23%
No FEC
Input Q-Factor (dB)
Ou
tpu
t B
ER
Input BERMotivation: Increase System Margin
»Increased System Capacity
»Decrease System Cost
»Longer Transmission Distances
»Increased Amplifier spacing
»Lower the optical power: less
pump power, less nonlinear
impairments
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Forward error correction (FEC)
2Q
© J.Wiley & Sons, Inc., 2003
coding gain= 6.0dB
10-9
10-3
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EXPERIMENTAL PROGRESS IN ERROR CORRECTION
10-15
10-12
10-9
10-6
10-3
10-6
10-5
10-4
10-3
10-2
10-1
SHANNON LIMIT 24% OH
Soft decision 24% OH
23% OH CONCAT. R-S
7% OH LDPC
7% OH R-S
No FEC
UNCORRECTED BER
CO
RR
EC
TE
D B
ER
~1990
2000
(AMCC)
2000 (Tyco)2003
(Mitsubishi)
Pre-1990
Pioneers: Reed-Solomon, Viterbi,…
Source: C. Chandrasekhar (Lucent)TLI: Nov 2004 - 33
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Block Turbo Code FEC*
*Mitsubishi Electric Corporation
T. Mizuochi, et al., OFC2003 PD-21
Q-Factor
~ 6.3 dB
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ELECTRONIC DISPERSION EQUALIZATIONin Enterprise Legacy LAN
(Scintera Networks)
• Large legacy infrastructure of installed Multimode Fiber
– Designed for “FDDI” at 300-m distance; supports 1GE
• Modal dispersion limits distance to 75 m at 10-Gb/s data rate
• LX4 uses CWDM: expensive and not commercially viable
IN OUTSCN3142
EDCE™
300-m Legacy Multimode Fiber; 1310 nm @ 10.3 Gb/sMeasured on Scintera Networks Production ICs
Enables Cost-effective 10G over Enterprise Legacy LAN
Source: A. Shanbhag (Scintera Networks)TLI: Dec 2003 – 36
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Electronic signal processing can mitigate PMD
Clock
BERD
PPGPMDE
10 Gb/s Tx
fiber
TD
FL
linear receiver
attenuator
Fig.1: DFL chip layout.
PMD distorted signal
Signal into feedback-
loop
recovered eye
Moeller, Thiede et al. ECOC 99
10 Gb/s
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the end
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Yariv