EE 233. LIGHTWAVE SYSTEMS Chapter 4. Optical Receiversee233/sp06/lectures/Chap_4_Optical... ·...

02/14/06 EE233. Prof. Kaminow 1

EE 233. LIGHTWAVE

SYSTEMS

Chapter 4. Optical

Receivers

Instructor:

Ivan P. Kaminow


PHOTODIODES

•PIN

•APD


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


depletion

depletion

R ~ 1 A/W

!

"


Intrinsic,

hi res

Also DH structure

(also waveguided)

! ~ 1,

W ~ 5µm


RECEIVER NOISE

•Shot noise

•Thermal noise


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


SHOT NOISE

•I(t) = Ip + is(t)

•White noise

• (s2 = <is

2(t)> = 2qIp$f

•Ip -> Ip + Id


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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


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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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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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


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


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


POWER PENALTY

•Increases Prec

•Transmission impairments•Chromatic dispersion•PMD•SPM, XPM•FWM

•Receiver impairments•Extinction ratio P0/P1

•RIN•Timing jitter


Desurvire


AGRAWAL(2005)-systems


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


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


Block Turbo Code FEC*

*Mitsubishi Electric Corporation

T. Mizuochi, et al., OFC2003 PD-21

Q-Factor

~ 6.3 dB


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


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


the end


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