performance analysis of scm optical transmission link for ... · eecs891 anthony leung april 23,...

EECS891EECS891

Anthony LeungAnthony LeungApril 23, 2004

Performance Analysis of SCM Optical Performance Analysis of SCM Optical Transmission Link for FiberTransmission Link for Fiber--toto--thethe--HomeHome

Department of Electrical Engineering & Computer Science, University of Kansas

Department of Electrical Engineering & Computer Science, University of Kansas 2

OutlineIntroduction

• Fiber-to-the-home & WDM-PON Approach• SCM Approach & Project Goal

SCM Network• SCM Network Architecture• Optical Modulator & Optical Signal Side Band Modulation• Noises Contribution in SCM Externally Modulated Optical Link

Transmission Link Performance Analysis• System Standard Requirements• CATV CNR Analysis & SCM Network Scalability Using Conventional MZ Modulator• Dual Parallel MZ Modulators• CATV CNR Analysis & SCM Network Scalability Using DPMZ Modulators• Digital Q-Value Analysis Uisng DPMZ Modulators

Fiber Nonlinearities• Stimulated Raman Scattering (SRS) Frequency Response• Cross Phase Modulation (XPM) Frequency Response• SRS+XPM Crosstalk analysis in SCM Network• Four-wave Mixing

Overall Transmission Performance Analysis Includes Signal-Crosstalk Noise

Conclusion & Future Work


Introduction: FTTH & WDM-PON

Technology Improvements

• Future Access Network “One for All” Architecture

Increasing Data Services Requirements

• Continued increasing data bandwidth demand• DSL & Cable Modem unlikely to meet longer

term needs

Competition • Entertainment Video Overlay

Cost Improvements • Cost of optoelectronic equipment continues to decline

• Reduced maintenance costs


ITU-T G.983.3 Wavelength Allocation Standard1.3 µm wavelength band (Upstream)

1260 13601340132013001280

G983.1 Upstream Band(unchanged at 100 nm bandpass)

Upstream Window (no change)Basic Band (constrained APON band)Enhancement Band (other uses)For future use

1360 14601440142014001380

Reserved for allocation by ITU-T Guard band

1480

Guard band

Intermediate wavelength band (Upstream and/or Downstream)

1.5 µm wavelength band (Upstream and/or Downstream)Enhancement BandBasic Band

ATM-PON

DownstreamGuard band Guard band

Future L Band

Reserved forallocation by ITU-T

λ 1λ

2λ

4λ

3λ

5λ

6

1.3 µm wavelength band (Upstream)

1260 13601340132013001280

G983.1 Upstream Band(unchanged at 100 nm bandpass)

Upstream Window (no change)Basic Band (constrained APON band)Enhancement Band (other uses)For future use

1360 14601440142014001380


1480

Guard band


1360 14601440142014001380


1480

Guard band


1.5 µm wavelength band (Upstream and/or Downstream)Enhancement BandBasic Band

ATM-PON


Future L Band


λ 1λ

2λ

4λ

3λ

5λ

6

Enhancement BandBasic Band

ATM-PON


Future L Band


1λ

2λ

4λ

3λ

5λ

6

ITU-T G.983.3 standard for Enhancement Band1.5µm wavelength Enhancement band (Upstream and /or Downstream)Application options at Enhancement Band (1539nm to 1560nm) are:1) Additional Digital Service Uses2) Video Distribution Service


WDM-PON Network Architecture

Video(RF)

Data Data

OLT(Optical Line Terminal)

Downstream1490 nm

Data Upstream1310 nm

1490nm/1310nm, 1550nm

DataData & Video

OpticalSplitter

EDFA(Erbium Doped Fiber Amplifier)

1310 nm 1490 nmDownstreamUpstream

DownstreamDigital Data

1550 nm

Video

Analog TV

550 MHz42 MHz

Upstream Digital Data

Bandwidths & Services

OpticalCouplers(WDM)

Video1550 nm

Central Office

Customer Premises

ONT(Optical Network Terminal)

E/O

Requires 3 Wavelengths Bandwidth to support Broadband ServicesRequires light source at customer home


SCM Approach

10 Km

1550 nm

FTTX ONT

Central Office/Hub Site

ONT

ONT

Power Splitter

1550 nm

1550 nm

DownstreamData at lower sideband of optical carrier (1550nm)Video at lower sideband of optical carrier (1550nm) Optical subcarrier at upper sideband of optical carrier (1550nm)UpstreamData at upper sideband of optical carrier (1550nm)

Use Microwave double side band technologyOptical modulated 78 CATV channel & 1 Gb/s digital data at the lower side band of optical carrier.At the same time, Optical modulated a sinusoidal RF signal at the upper side band of optical carrier and deliver from CO to Customer, this optical RF signal is used as optical light source for upstream data transmission. Therefore, no laser source requires at customer side.

78 CATV 1Gb/s dataSinusoidal Signal

Upstream digital data


Project GoalExamine Physical Transmission Performance Using SCM Approach transmitting 78 CATV channel and 1Gb/s digital channel from CO to Customer Premises

• Analyze 78 Analog CATV Carrier-to-Noise Ratio (CNR) Performance

• Analyze 1Gb/s Digital Channel Q-Value Performance

• Analyze the fiber crosstalk in SCM Network• Stimulated Raman Scattering (SRS)• Cross Phase Modulation (XPM)• Four wave Mixing (FWM)

• Evaluated the Overall Transmission Performance due to fiber crosstalk

This project is the first time to demonstrate for this comprehensive analysisusing microwave double side band technology for FTTH application


SCM Network Architecture

CA

TVC

hann

el 2

CA

TVC

hann

el 7

8

1Gb/

s da

tado

wns

tream

CCATV

Channel 2

CATVChannel 78

f1

f78

1Gb/s datadownstream

fd

2π

Σ o90

o0

Laser

FPI

O/E

f78 fd

Σ

f1

UpstreamData

O/EUpstream

Data

C

Splitter

OptFilter

Central Office (CO)

10 Km

FPIReflection

FPITransmission

G

CCCirculator Circulator

Hyb

rid

Customer Premise

Sinusoidal RF signal


Optical Modulation & MZ Modulator

RF ∆θ =

RF ∆θ =

RF ∆θ =

Optical ∆ψ =Optical ∆ψ =Optical ∆ψ =

)cos( θω +ts

Optical Input Optical OutputDC

AC

AC

Bias

+++

++= )cos(coscoscos

2)( θωπωωππω

πππ

tVVtt

VV

VVtAtE i

acci

acdcco

Optical Output

2π

−

ω0-ωS ω0 ω0+ωS

ω0 ω0+ωS ω0-ωS ω0

ω0-ωS ω0 ω0+ωS ω0-ωS ω0 ω0+ωS

ω0-ωS ω0 ω0 ω0+ωS

π

2π

2π

− π2π

)cos( tsω

Optical Phase Difference between Upper and Lower arms of MZ Modulator

RF Phase Difference between Upper and Lower arms of MZ Modulator

[1]


Optical Single Side Band Modulation

Optical Input Optical OutputDC

AC

AC

Optical Output

90º

0º

CATVChannel 2

CATVChannel 78

f1

f78

1Gb/s datadownstream

fd

S

78 RF Modulated Video streams: tcAts miciii

i )cos()(78

1ωω −⋅= ∑

=Downstream digital RF Channel: )cos()()( ttxts dd ω⋅=

Upstream RF Channel: )cos()( tts uu ω=

Analog TV Digital Ch.Optical RFSubcarrier

2πV

Vdc =

44MHz to 550MHz

[ ]

−−

+−

−+−

−=

∑=

tV

AJE

ttxV

AJE

tV

AJE

ttV

AJEtE

uci

dci

imici

cci

)cos()(

)cos()()(

))(cos()(

)sin()cos()(2

)(

1

1

78

11

0

ωωπ

ωωπ

ωωωπ

ωωπ

π

π

π

π

Hyb

rid


Noise Contributions in Optical Transmission

Thermal Noise: Noise is generated in resistive elements (Photo-detector)Shot Noise: Noise is generated when an optical signal is incident on the photo-detectorRIN Noise: Noise is generated by spontaneous emission with the laser sourceBooster Amplifier Noise: Noise generated by AmplifierClipping: It set the fundamental limitation on how much the laser can be clipped for composite input signalIntermodulation Distortion: Composite second order (CSO) & Composite Triple Beat (CTB) generated by Conventional MZ Modulator

Thermal Noise Limited Shot Noise Limited RIN Noise Limited ASE Noise Limited

Optical Receiver Power Increase

G

ASE Noise

Analog orDigital Data

RF Carrier

Χ

Thermal NoiseShot Noise

Laser MZ Modulator

Analog orDigital Data

RF Carrier

Χ

RIN Noise &Clipping CSO/CTB

Ps Pase , GPs

LPase ,GLPs


Nonlinear Distortions (CSO, CTB) of Convention MZ ModulatorTransfer function of MZ modulator is a sine wave-like function of input voltage

Composite Second Order (CSO) : Max 79 CSO Distortion terms fall at RF channel 1 Composite Triple Beat (CTB) : Max 2185 CTB distortion terms fall at RF channel 38

))(cos(222

)(

cos 2 θπθπ

π

π −+=

−⋅=

VtVPPV

tV

PP ooos

0 10 20 30 40 50 60 70 80-20

0

20

40

60

80Second Order product count vs. RF Channel Index

Num

ber o

f Ter

ms

fa-fbfa+fb

0 10 20 30 40 50 60 70 801400

1600

1800

2000

2200Third Order product count vs. RF Channel Index

RF Channel Index

Num

ber o

f Ter

ms


Nonlinear Distortions (CSO, CTB) of Convention MZ ModulatorPower ratio of CSO/C

2

2

101

20

21

})sin(

)cos({

)]()[(2

)]([)]([2

dc

dc

CSON

N

VV

VV

N

VAJ

VAJ

VAJ

VAJ

CCSO

π

π

ππ

ππ

π

π

ππ

ππ

⋅

=−

−

Power ratio of CTB/C

2

2

101

30

31

})sin(

)sin({

)]()[(2

)]([)]([2

dc

dc

CTBN

N

VV

VV

N

VAJ

VAJ

VAJ

VAJ

CCTB

π

π

ππ

ππ

π

π

ππ

ππ

⋅

=−

−

• CSO Cancelled when Applied DC Voltage bias at ±0.5Vπ ,±1.5Vπ,…(Q-point)

• CTB independent of Applied DC Voltage

• CSO is negligible

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

-80

-60

-40

-20

0

20

CTB/C, CSO/C vs. Applied DC bias voltage (OMI=5%)

Applied Bias DC Voltage normalized to Vpi

CTB

/C, C

SO/C

(-dB

c)

CSO/CCTB/C


Transmission Standard & Device Parameter Values

666Digital Q-Value

-60dBc-53dBc +/- 2dB> 51dBc [Section 76.605 (a) (8)]CATV CTB

-60dBc-53dBc +/- 2dB> 51dBc [Section 76.605 (a) (8)]CATV CSO

50dB48dB +/- 2dB > 43dB [Section 76.605 (a) (7)] CATV Carrier/Noise

Project TargetTypical ValueFCC RequirementParameter

Laser MZ Modulator Booster Amplifier Photodiode Power = 6, 8 &10dBm Loss=5dB Input Power -1, 1 & 3dBm Responsivity = 0.8, 0.9A/W

Wavelength = 1550nm Bandwidth = 20GHz Output Power = 17dBm BW = 6MHz (CATV)

RIN=-155, -160dB/Hz Noise Figure = 5dB BW = 0.75GHz (Digital)

nsp = 1.5849 T=300K, Kb=1.38e-23

Coupling and Isolator loss = 2dB Resistance = 1000 ohms


CATV CNR Analysis using Conventional MZ Modulator

Parameter Values Optical Power budget : 1 end UsersRIN=-155dB/Hz-1dBm input at Booster AmplifierR=0.8 A/W

• CNR=43.1dB (Maximum)C/CTB = 47dB OMI = 1.84%

• Disregarding CTB term for the moment:1) CNR increases to 50dB, as OMI increases to 3.4% OMI.

2) As OMI continues to increase, Clipping becomes dominant

3) Optimized OMI from 3% to 5% range

( ) 14

13

21

21

21

221

221

2

221

1111111

]16[]612[]8

[]4

[]8

[]2

[2

−−−−−−−

−−−−−−−

⋅+

+++++

⋅=

+++++=

ctbsp

s

p

pp

p

ptotal

CTBClippingASEshotThermalRINtotal

Nme

RBhfnIm

BqIIm

RKTB

Im

BIRIN

ImCNR

CNRCNRCNRCNRCNRCNRCNR

µµπ µ

10-4

10-3

10-2

10-1

100

101

0

10

20

30

40

50

60

70

80CNR vs OMI with one Remote Unit

OMI

CN

R

ASE Noise Shot Noise RIN Noise Thermal Noise Laser ClippingCTB CNR


Scalability of SCM network using Conventional MZ ModulatorParameters Line 1 Line 2 Line 3 Line 4

Input power at Booster Amplifier -1dBm 1dBm 1dBm 3dBm

Laser RIN -155dB/Hz -155dB/Hz -160dB/Hz -160dB/Hz

Photodiode Responsivity 0.8 A/W 0.8 A/W 0.9A/W 0.9 A/W

Fiber distance 10km 10km 10km 10km

The “SCM/WDM-PON” network scalability can not be improved further as the third order nonlinear distortion (CTB) severe limit overall CNR performance It cannot implement in practical CATV network without reduced CTB noise

Increase SCM Network Scalability

Improved ASE NoiseImproved Laser RIN NoiseImproved Receiver Noise

0 10 20 30 40 50 6039

40

41

42

43

44

45

46CNR vs Number End-Users

Number of End-users

CN

R (d

B)

Line1Line2Line3Line4


Dual Parallel Linearized External Modulators

Primary Modulator bias at Q-point (Vdc = 0.5Vπ)Secondary Modulator bias at Q-point 180º from the point chosen for the primary modulator (Vdc = 1.5Vπ)Apply higher RF driver power and less Optical power to secondary modulator. This result higher OMI and higher distortion. CTB created in secondary modulator can be made to cancel the distortion products from the primary modulator [2]

Transfer Function of DPMZ

A = Optical Power Ratio B = RF Power Ratio

−−+=

−−+

−=

ππ

ππ ππππππ

VtVBA

VtVA

VtVB

AV

tV

APP

in

out )(sin)1()(sin121

22

3)(

cos)1(2

2)(

cos 22

Primary ModulatorTransfer Function

Secondary ModulatorTransfer Function

Laser 1

Laser 2

V(t) + Vbias 1

BV(t) + Vbias 2

)))(sin(1(21 tV

VP

p

p+

)))(sin(1(22 tBV

VP

p

p-

Laser

V(t) + Vbias 1

)))(sin(1(2

tVV

PAp

p+

)))(sin(1(2

)1( tBVV

PA

p

p--

Approach # 1BV(t) + Vbias 2

A

1-A

Powerdivider

PrimaryModulator

SecondaryModulator Secondary

Modulator

PrimaryModulator

PhaseModulator

Approach # 2

)))(sin()1())(sin(1(2

tBVV

AtVV

AP

pp

pp --+


0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10.8

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

1DPMZ Power Divider Ratio vs. OMI

Optical Modulation Index m

Pow

er D

ivid

er R

atio

(A)

B=2 B=2.5B=3

Dual Parallel Linearized External Modulators1

011

01 )()()1()()( −− −−= NN

in VABJ

VABJA

VAJ

VAAJ

PP

k

ππππ

ω ππππ

30

31

30

31 )()()1()()( −−++

−−= NN

in VABJ

VABJA

VAJ

VAAJ

P

Pkjk

ππππ

ωωω ππππ

30

31

30

31

30

31

)()()()(

)()(

−−

−

+=

NN

N

VABJ

VABJ

VAJ

VAJ

VABJ

VABJ

A

ππππ

ππ

ππππ

ππ

Amplitude of Fundamental carrier with frequency ωk

Amplitude of third order distortion component of the frequency ωi+ωj+ωk

B = 2, A =0.87 to 0.89

B = 2.5, A =0.92 to 0.94

B = 3, A =0.94 to 0.97

The optimize value of OMI is from 3% to5%, Laser clipping becomes dominant asOMI increases to 5%


DPMZ

Case I: A=0.88, B=2, OMI = (1% - 4.5%), CTB/C > 60 dB

Case II: A=0.93, B=2.5, OMI = (1% - 4.4%), CTB/C > 60 dB

Case III: A=0.96, B=3, OMI = (1% - 3.4%), CTB/C > 60 dB

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

20

40

60

80

100

120

C/CTB Performance with B=2.5 and A=0.92, 0.93 & 0.94

OMI

C/C

TB (d

B)

A=0.92 & B=2.5 A=0.93 & B=2.5 A=0.94 & B=2.5 Nonlinearized modulator

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

20

40

60

80

100

120

C/CTB Performance with B=2 and A=0.87, 0.88 & 0.89

OMI

C/C

TB (d

B)

A=0.87 & B=2 A=0.88 & B=2 A=0.89 & B=2 Nonlinearized modulator

0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

20

40

60

80

100

120

C/CTB Performance with B=3 and A=0.94, 0.95, 0.96 & 0.97

OMI

C/C

TB (d

B)

A=0.94 & B=3 A=0.95 & B=3 A=0.96 & B=3 A=0.97 & B=3 Nonlinearized modulator

C/C

TB (d

B)

Best Case when B=2

Best Case when B=3

Best Case when B=2.5


CATV CNR Analysis Using Linearized MZ Modulator

Parameter ValuesLinear Modulator

• A = 2 & B = 0.88

Optical Power budget • 8 Customers• 30 Customers• 60 Customers

RIN=-155dB/Hz-1dBm input at Booster AmplifierR=0.8 A/W

Results• Optical Power Budget = 8

Customers• CNR=50dB • C/CTB = 60.5dBc

OMI = 4.48%10

-410

-310

-210

-110

010

10

10

20

30

40

50

60

70

80CNR vs OMI using Case I linearized Modulator

OMI

CN

R

ASE Noise Shot Noise RIN Noise Thermal Noise Laser Clipping CTB CIR5 CNR 8 end-users CNR 30 end-usersCNR 60 end-users


Scalability of SCM Externally M0odulated Optical Link Using DPZMPARAMETERS Line 1 Line 2 Line 3 Line 4

Case I : MZ Modulator A=0.88 & B=2

A=0.88 & B=2

A=0.88 & B=2

A=0.88 & B=2

Input power at Booster Amplifier -1dBm 1dBm 1dBm 3dBmLaser RIN -155dB/Hz -155dB/Hz -1 60dB/Hz -160dB/Hz

Photodiode Responsivity 0.8 A/W 0.8 A/W 0.9A/W 0.9 A/WFiber distance 10km 10km 10km 10km

RESULTSNo. of End -Users > 50dB CNR 8 15 22 27

CNR per Channel 50 dB 50.1163 dB 50.0553dB 50.0079 dBC/CTB per Channel 60.4695 dB 60.6555 dB 60.65dB 60.655dB

OMI per Channel 4.48 % 4.47 % 4.47 % 4.47%Receiver Optical Power per RF Channel -13.647dBm -16.37dBm -18dBm -18.9dBm

0 10 20 30 40 50 6045

46

47

48

49

50

51

52

53

54

55CNR vs. Number End-Users using Case I Linear Modulator

Number of End-users

CN

R (d

B)



Scalability of SCM Externally Modulated Optical Link Using DPZMPARAMETERS Line 1 Line 2 Line 3 Line 4

Case II: MZ Modulator A= 0.93 & B=2.5

A=0.93 & B=2.5

A=0.93 & B=2.5

A=0.93 & B=2.5

Input power at Booster Amplifier -1dBm 1dBm 1dBm 3dBmLaser RIN -155dB/Hz -155dB/Hz -160dB/Hz -160dB/Hz

Photodiode Responsivity 0.8 A/W 0.8 A/W 0.9A/W 0.9 A/WFiber distance 10km 10km 10km 10k m


CNR per Channel 50.036 dB 50.085 dB 50.043dB 50.08 dBC/CTB per Channel 61.9 dB 61.89dB 61.89dB 61.89dB

OMI per Channel 4.34 % 4.34 % 4.34 % 4.34%Receiver Optical Power per RF Ch -14.8dBm -16.8dBm -18.1dBm -18.8dBm

0 10 20 30 40 50 6044

46

48

50

52

54

56CNR vs. Number End-Users using Case II Linear Modulator

Number of End-users

CN

R (d

B)



Scalability of SCM Externally Modulated Optical Link Using DPZMParameters Line 1 Line 2 Line 3 Line 4

Case III: MZ Modulator A=0.96 & B=3

A=0.96 & B=3

A=0.96 & B=3

A=0.96 & B=3

Input power at Booster Amplifier -1dBm 1dBm 1dBm 3dBmLaser RIN -155dB/Hz -155dB/Hz -160dB/Hz -160dB/Hz

Photodiode Responsivity 0.8 A/W 0.8 A/W 0.9A/W 0.9 A/WFiber distance 10km 10km 10km 10km


CNR per Channel 49.47 dB 50.062 dB 50.1182dB 50.05 dBC/CTB per Channel 60.0191 dB 60.0191dB 60.0191dB 60.0191dB

OMI per Channel 3.43 % 3.43 % 3.43 % 3.43%Receiver Optical Power per RF Channel -4.6dBm -12.38dBm -15.9dBm -17.6dBm

0 10 20 30 40 50 6043

44

45

46

47

48

49

50

51

52

53CNR vs. Number End-Users using Case III Linear Modulator

Number of End-users

CN

R (d

B)



Digital Data Q-Value Analysis})cos()()()()1(2)cos()()()(2{ 1

011

01

⋅⋅−−

⋅⋅⋅= −− ttx

VVBJ

VVBJAttx

VVJ

VVAJII d

Nd

Np ωππωππ

ππππ

)(2

})2

)(1(2)2

(2{2

)1()1()1()1(

4/4/ 222

ASEThermalRINShot

NmBNm

PPBPSK

eBmAemAIIIQ

σσσσσσ +++

−−

⋅⋅

=−+−−

=

−−

)(2

})2

)(1(2)2

(2{

)2

1()2

1(

)2

1()2

1( 4/4/ 222

ASEThermalRINShot

NmBNmPP

QPSK

eBmAemAIIIQ

σσσσσσ +++⋅

−−

⋅

=−+

−−=

−−

)(2

})2

)(1(2)2

(2{

)0()1()0()1(

4/4/ 222

ASEThermalRINShot

NmBNm

PPASK

eBmAemAIIIQ

σσσσσσ +++

−−

⋅

=+−

=

−−

Parameter Set 1 Set 2 Set 3Linear MZ Modulator A=0.88 & B=2 A=0.93 & B=2.5 A=0.96 & B=3

Input power at Booster Amplifier 3dBm 3dBm 3dBmLaser RIN -160dB/Hz -160dB/Hz -160dB/Hz

Photodiode Responsivity 0.9 A/W 0.9 A/W 0.9A/WFiber distance 10km 10km 10km

No. of End-Users 27 30 18OMI / Channel 4.47% 4.34% 3.43%

Receiver Optical Channel Power -18.9dBm -18.8dBm -17.6dBm


Digital Data Q-Value Analysis

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.050

5

10

15

20

OMI at 27 End-Users Optical Power Budget

Q

BPSKQPSKASK

-24 -22 -20 -18 -16 -14 -12 -10 -8 -6 -40

10

20

30

40

Receiver Optical Power per Channel at 4.47% OMI

Q

BPSKQPSKASK

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.050

5

10

15

20Set 3


Q

BPSKQPSKASK

-24 -22 -20 -18 -16 -14 -12 -10 -8 -6 -40

10

20

30

40


Q

BPSKQPSKASK

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.050

5

10

15

20

Set 1 Set 2 Set 3RESULTSBPSK Q-Value 14.3 15.7 16.9QPSK Q-Value 10.1 11 11.9ASK Q-Value 7.2 7.8 8.4

Set 1 Set 2


Q

BPSKQPSKASK

-22 -20 -18 -16 -14 -12 -10 -8 -6 -40

10

20

30

40


Q

BPSKQPSKASK

1) The Requirements of Digital is more relax compared to Analog channel.

2) High Optical Power Transmission in SCM Network

3) Q-Value continues to increase as optical power increase


Fiber Nonlinearities (From Linear to Non-linear Propagation)

Types of Fiber NonlinearitiesStimulated Scattering• Raman (SRS)

Nonlinear index (Kerr Effect)• Cross-phase modulation (XPM)• Four-wave mixing (FWM)

λSRS

λFWM


Stimulated Raman Scattering (SRS) Frequency Response Concept in WDM Network [3]

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 109

-85

-80

-75

-70

-65

-60

-55

-50

-45SRS Frequency Response

Modulation Freqency (Hz)

SRS

(dB

)

1nm frequency spacing4nm frequency spacing8nm frequency spacing

Parameter ValuesSM fiber, Slope of Raman Gain = 5e-15m/W/THz10dBm optical power entering fiber10km fiber lengthDispersion = 17ps/nm/km

• Transfer Function of SRS has a low pass filter characteristic

• SRS increases, as the Frequency Spacing between two channel increases.

• SRS is dominant at high frequency spacing and at small modulation frequency

121

1

1 )(1 IgItI

zI

αν

−=∂∂

+∂∂

212

2

2 )(1 IgIt

IzI

αν

−−=∂∂

+∂∂

−−=

+−≈

−−−− ∫ α

µµµα

αααz

oeff

zo

z z

eff

z ePAgePdzezdP

AgePP 11),0(1),0(),0(

0

''12212222

'

−+=

++≈

−−−− ∫ α

µµµα

αααz

oeff

zo

z z

eff

z ePAgePdzezdP

AgePP 11),0(1),0(),0(

0

''12121111

'

λ2 λ1

Optical Carrier power after fiber loss

Interaction between the opticalcarriers, results in optical dc power gain or loss

Use coupled propagation equations to solve for SRS Crosstalk level


Cross Phase Modulation (XPM) Frequency Response Concept in WDM Network [4]

PumpChannel K

ProbeChannel J

),()],(2[),(

2),(1),(

2),(

2

22 ztAzzdtPi

tztAi

tztA

ztAz

ztAjjkkj

jj

jj

j −=∂

∂+

∂

∂++

∂

∂γ

βν

α

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 109

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30XPM Frequency Response


XPM

(dB

)

1nm frequency spacing4nm frequency spacing8nm frequency spacing

Fiber Loss Linear Phase Delay Phase Modulation in the channel J induced by channel k

Fiber Dispersion results in convert Phase Modulation to Intensity Modulation

Parameter Values10dBm optical power entering fiber10km fiber lengthDispersion = 17ps/nm/km

• XPM transfer function has a high pass filter characteristic

• XPM increases, as the Frequency Spacing between two channel decreases.

• XPM is dominant at small frequency spacing and at large modulation frequency


Constructive & Destructive SRS+XPM Frequency Response Concept inWDM Network [3]

Channel 2 CWChannel 1

CWChannel 2 Channel 1

Crosstalk at Channel 1 (Constructive)Power gain through SRS InteractionXPM crosstalk at Channel 1

Crosstalk at Channel 2 (Destructive)Power depletion through SRS InteractionXPM crosstalk at Channel 2

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 109

-80

-70

-60

-50

Crosstalk Frequency Response at Channel 1

Xta

lk F

requ

ency

Res

pons

e

Constructive CrosstalkSRS XPM

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

x 109

-80

-70

-60

-50

Crosstalk Frequency Response at Channel 2


Xta

lk F

requ

ency

Res

pons

e

Destructive CrosstalkSRS XPM

• SRS dominant for small modulated frequency or large wavelength separation

• XPM is dominant for large modulated frequency or small wavelength separation

• In between we must consider whether the Channel suffered by SRS is going through power gain or depletion

Parameter Values10dBm optical power entering fiber10km fiber length17ps/nm/km Dispersion0.8 nm Frequency spacing


SRS+XPM crosstalk in SCM Externally Modulated Network

CATV Ch.Digital Ch.1 2 78

1GHz to 10GHz frequency spacings6MHz

0 1 2 3 4 5 6

x 106

-280

-260

-240

-220

-200

-180

-160

-140Crosstalk Frequency Response (SRS & XPM)


Cro

ssta

lk F

requ

ency

Res

pons

e (d

B)

6MHz Wavelength separation 60MHz Wavelength separation 0.6GHz Wavelength separation6GHz Wavelength separation

Parameter ValuesOptical Power Budget = 30 End-Users-15.6dBm optical channel power entering fiber 10km fiber length, 0.22dB/km5e-15m/W/THz SRS Gain Slope17ps/nm/km Dispersion


SRS+XPM Crosstalk in SCM Externally Modulated Network

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18-120

-110

-100

-90

-80Crostalk Optical power(dBm) vs. Wavelength Separation (nm)

Cro

ssta

lk O

ptic

al P

ower

(dB

m)

SRS XPM Crosstalk(SRS+XPM)

Wavelength Separation (nm)0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

-110

-100

-90

-80

-70

-60Crosstalk optical power normalized to transmitted ch. power vs. Wavelength Separation (nm)

Cro

ssta

lk le

vel (

dB)

SRS XPM Crosstalk(SRS+XPM)

Wavelength Separation (nm)

SRS is the dominant crosstalk compared to XPM

Overall result, SRS & XPM crosstalk shows very minimal impact between two subcarrier under same wavelength


Four-Wave Mixing

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18-86

-84

-82

-80

-78Ratio of FWM power to transmitted ch. power vs. Wavelength Separation(nm)

Wavelength Separation(nm)

FWM

cro

ssta

lk le

vel

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18-104

-102

-100

-98

-96FWM optical power (dBm) vs. Wavelength Separation (nm)

FWM

opt

ical

pow

er (d

Bm

)


ηλπ 2

22

1111224

6

)()(1024)( effeff

kjiijk L

A

PPPDX

cnLP =

Parameter ValuesOptical Power Budget = 30 End Users-15.6dBm optical channel power entering fiber 10km SM standard fiber 17ps/nm/km DispersionD=6 (None of Frequencies are the same)


Total Crosstalk in SCM Externally Modulated Network

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16-95

-90

-85

-80

-75

-70

-65Crosstalk level vs. Wavelength Separation(nm)


Cro

ssta

lk le

vel (

dB)

Total CrosstalkFWM SRS+XPM

FWM is the major source of nonlinear crosstalk in SCM optical systems with extremely narrow spacing between RF channels

SRS becomes dominant as channel spacing increases



CATV Ch.Digital Ch.1 2 78

1GHz to 10GHz frequency spacings6MHz

0 10 20 30 40 50 60 70

-58.9

-58.8

-58.7

-58.6

-58.5

-58.4

-58.3

-58.2

Crosstalk (dB) per Individual CATV Channel

Cro

ssta

lk le

vel (

dB)

78 CATV Channel Index

1 2 3 4 5 6 7 8 9 10-57

-56

-55

-54

-53

-52

-51

-50

-49Crosstalk (dB) at Digital Channel

Frequency Spacing (GHz)

Cro

ssta

lk le

vel (

dB)

Freq. Spacing between Digital Ch. and CATV ch. # 78



The CATV Crosstalk level remains constant as power increases because FWM is the dominant Crosstalk at narrow channel spacing

It demonstrates that as optical power increases, FWM becomes the dominant crosstalk in SCM externally modulated Network

-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0-65

-60

-55

-50

-45

-40

-35

-30

-25Crosstalk level at channel power at CATV Channel 1

Input fiber optical channel power (dBm)

Cro

ssta

lk le

vel (

dB)

1GHz spacing from digital ch. 2GHz spacing from digital ch. 3GHz spacing from digital ch 4GHz spacing from digital ch. 5GHz spacing from digital ch. 6GHz spacing from digital ch. 7GHz spacing from digital ch. 8GHz spacing from digital ch. 9GHz spacing from digital ch. 10GHz spacing from digital ch.

-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0-65

-60

-55

-50

-45

-40

-35

-30

-25Crosstalk level at Digital Channel

Input fiber optical channel power (dBm)

Cro

ssta

lk le

vel (

dB)

1GHz spacing from CATV 2GHz spacing from CATV 3GHz spacing from CATV 4GHz spacing from CATV 5GHz spacing from CATV 6Hz spacing from CATV 7GHz spacing from CATV 8GHz spacng from CATV 9GHz spacing from CATV 10GHz spacing from CATV


Signal-crosstalk Noise in SCM Transmission Performance for CATV PARAMETERS Case 1 Case 2

Linearized MZ Modulator A=0.93 & B=2.5 A=0.93 & B=2.5 Input power at Booster Amplifier -1dBm 3dBm

Laser RIN -155dB/Hz -160dB/Hz Photodiode Responsivity 0.8 A/W 0.9 A/W

Fiber distance 10km 10km OMI 4.343% 4.343%

-22 -20 -18 -16 -14 -12 -10 -8 -6 -425

30

35

40

45

50

55

60CNR vs. Receiver optical power per RF channel

Receiver optical power per channel

CN

R(d

B)

Case 1 CNR (no crosstalk) Case 2, CNR (no crosstalk) Case 1 CNR (with crosstalk)Case 2 CNR (with crosstalk)


Signal-crosstalk Noise in SCM Transmission Performance for Digital DataPARAMETERS

Linearized MZ Modulator A=0.93 & B=2.5 Input power at Booster Amplifier 3dBm

Laser RIN -160dB/Hz Photodiode Responsivity 0.9 A/W

Fiber distance 10km OMI 4.343%

-22 -20 -18 -16 -14 -12 -10 -8 -6 -44

6

8

10

12

14

16

18

20

22BPSK, QPSK & ASK vs. Receiver Optical power at Digital RF Channel

Receiver Optical Power per Channel

Q

BPSK

QPSK

ASK


Conclusion

Transmission Quality• Optimizing the Receiver Optical Power per RF Channel = -17dBm to -20dBm• CATV CNR in the range of 48dB to 48.5dB• Digital BPSK Q = 13 to 17• Digital QPSK Q = 9 to 12• Digital ASK Q = 6 to 8

Network Scalability• Number of Customers premises = 20 to 40

0 10 20 30 40 50 6025

30

35

40

45

50

55

60CATV CNR vs. Customer Premise

Number of Customer Premise

CN

R (d

B)

Case 1 CNR (no crosstalk) Case 2, CNR (no crosstalk) Case 1 CNR (with crosstalk)Case 2 CNR (with crosstalk)

0 10 20 30 40 50 604

6

8

10

12

14

16

18

20

22BPSK, QPSK & ASK Q Value vs. Customer Premise

Number of Customer Premise

Q

BPSK

QPSK

ASK


Future Work

Analyze the uplink transmission performance and the impact of optical crosstalk under bi-directional fiber transmission.

Analyze uplink multiple access method such as Time Division Multiple Access (TDMA), Subcarrier Multiple Access (SCMA) and their efficiencies.

Because Narrow-band optical filter is relative expensive compared to wide-band optical filter, further study in separate upper and lower side-band of optical carrier at end-user is suggested.

The even-order distortion produced by a MZ modulator can be cancelled using OSSB Modulation. CSO is also affected by various phenomena such as chirp, fiber chromatic dispersion and polarization-mod dispersion (PMD), self-phase modulation (SPM) as well as gain-tilt of optical amplifiers. Future study in CSO distortion in SCM externally modulated optical network is suggested.


Acknowledgements & Questions

Many Thanks to:

Dr. Hui for his guidance throughout this project

Dr. Frost and Dr. Saiedian for their service on the project committee

Questions?


References cited in this presentation:

[1] R. Hui, B. Zhu, R. Huang, C. Allen, K. Demarest, D. Richards, “Subcarrier Multiplexing for High-speed Optical Transmission,” Journal of Lightwave Technology, vol. 20, no. 3, March 2002

[2] J. Brooks, G. Maurer, R. Becker, “Implementation and Evaluation of a Dual Parallel Linearization System for AM-SCM Video Transmission,” Journal of Lightwave Technology, vol. 11, no. 1, January 1993.

[3] M Phillips & D. Ott, “Crosstalk Due to Optical Fiber Nonlinearities in WDM CATV Lightwave Systems,” Journal of Lightwave Technology, vol 17, no. 10, Oct. 1999.

[4] R. Hui, Y. Wang, K. Demarest, C. Allen, “Frequency Response of Cross-Phase Modulation in Multispan WDM Optical Fiber Systems,” IEEE Photonics Technology letters, vol 10, no. 9, September, 1998

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