Simulation and Experimental Study of SCM/WDM Optical Systems by warrent

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									Simulation and Experimental Study of SCM/WDM Optical Systems
Renxiang Huang University of Kansas May 23, 2001

Outline
s

Introduction to SCM technology
s s s

Demand for more bandwidth TDM,WDM strategies SCM and WDM combination

s

Numerical simulation model
s s

Goals and general requirements Description of the simulation model s Transmitter s Optical fiber nonlinear model s Receiver

Outline
s

Simulation results
s

s

s

s

BPSK, 4-subcarrier each with 2.5Gb/s datarate, self-coherent detection QPSK, 2-subcarrier each with 2x2.5Gb/s datarate, selfcoherent detection ASK, 4-subcarriers each with 2.5Gb/s datarate, direct detection using narrowband optical filter Traditional NRZ modulated OC192 system

s

Experiment Conclusions and future work

s

Introduction: Demand for more Bandwidth
s s s s s

Faster Internet access High speed data transmission Video Conferencing High resolution image transmission Other new services

s s s

More fiber everywhere Higher data-rate each wavelength----------TDM More wavelengths in the fiber--------------- WDM

Introduction: TDM,WDM strategies

s

TDM strategy
s s s s s

s

Simple modulation format: IMDD binary system Short bit length, more bits in unit time Electrical TDM and optical TDM, soliton Grooming may be a big problem Difficult in transmission through fiber: chromatic dispersion, PMD, fiber nonlinearity Does not scale well beyond OC192

Introduction: TDM,WDM strategies
s

WDM strategy
s s s s

Multiple wavelengths in a single fiber Better utilization of optical fiber transmission window Lower bitrate & lower power per wavelength From CWDM to DWDM: increase bandwidth efficiency
example:2.5Gb/s per-channel data rate and 50GHz channel spacing, the example: bandwidth efficiency is 0.05 bit/Hz.

s

Technical difficulties: lightwave sources, optical filters, dispersion management, nonliear crosstalk, ….

Introduction: SCM/WDM and OSSB
s s

s

SCM leverages mature microwave technology Two-step modulation: RF modulation at sub-carriers, optical modulation at wavelengths. OSSB is preferred: less dispersion penalty, higher bandwidth efficiency

f4 -

f3 -

f2a.

f1 -

fO

f1 +

f2 +

f3 +

f4 +
o p tic a l d e te c tio n u s in g filte r

O ptic al D S B S C M

fO b.

f1 +

f2 +

f3+

f4 +

O ptic al S S B S C M

Introduction: SCM/WDM and OSSB
s

SCM/WDM combination
s

s s

Large number of channels, low channel speed, easy grooming and scaling, lower dispersion penalty Advanced modulation format, phase modulation possible Nonliearity-introduced distortion

λ1
a.

λ2
W D M /S C M

f1 +

f2 +

f3+

f4 +

λ1
b. W DM

λ2

An exemplary setup of SCM/WDM system
Transmitter f1 λ1 ch.1 f2 ch.2 . . ch.n
Σ Σ

Receiver f1 ch.1 f2 fn ch.2 . . ch.n

fn
Optical WDM DMUX Optical WDM MUX

Add/drop

λ1

Transmitter f1 ch.1 f2 ch.2 . . ch.n
Σ

Receiver f1 λm
Σ

ch.1 f2 fn ch.2 . . ch.n

fn λm

5GHz

50GHz

λ1

λ2

λ3

λ4

λ

Numerical model for SCM/WDM systems
s

Goals and general requirements
s

s s

s

To be able to handle different types of multi-wavelength SCM/WDM systems Include both dispersion and fiber nonlinearity To be able to handle a variety of modulation formats, OSSB, ASK, BPSK, QPSK and binary IMDD Combine waveform distortion and noise: sensitivity

Transmitter simulation model
C ha nne l 1 d a ta 2 . 4 8 8 G b it/s T ra ns m itte r fiilte r

C ha nne l 1 R F o s c illa to r (3 . 6 G H z) c ha nne l 2 (8 .3 G H z) c ha nne l 3 (1 3 G H z) C ha nne l 4 d a ta 2 . 4 8 8 G b it/s RF m u ltip le xe r

T ra ns m itte r filte r

C ha nne l 4 R F o s c illa to r (1 7 .5 G H z)

9 0 d e gre e p ha s e s hift

to f iber W D M c o u p le r

Power a m p lifie r

M Z m o d u la to r

LD

f ro m o ther laser so urses

B ia s

S C M T ra n sm itter B lo ck D ia g r a m

Baseband signal generation

s s

s s

27-1 PRBS Random relative delay between different sub-carriers and wavelengths 6-order Butterworth filter for band-limiting 64 to 256 samples per bit depending on the required simulation bandwidth

Baseband signal generation
4 0 0 0 C h a n n e l N u m b e r= 1 C h a n n e l W a v e le n g t h = 1 5 5 0 N u m b e r o f s a m p le s /b it= 6 4 n m 3 5 0 0 3 0 0 0 2 5 0 0

•Signal eyediagram

2 0 0 0

1 5 0 0

1 0 0 0

5 0 0

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 1 4 0 0 1 6 0 0 1 8 0 0

w )

I c h a n n e l 4 0 0 0

(a)eyediagram of baseband signal after the electrical filter
T R A N S M IT F IL T E R O U T P U T P U L S E -- > IN T E N S IT Y a ft e r fi lt e r in g C h a n n e l N u m b e r = 1 B it R a t e = 2 . 4 8 G b / s C h a n n e l W a v e le n g t h = 1 5 5 0 C a r r ie r fr e q u e n c y = 2 . 6 G H z n m

(m

u ls e

•Signal waveform

in t e n s it y

3 0 0 0

2 0 0 0

1 0 0 0

0

P

- 1 0 0 0

- 2 0 0 0 0 0 . 5 1 1 . 5 2 2 . 5 T im e 3 ( p s ) 3 . 5 4 4 . 5 x 5 1 0
4

1

0 5 0 - 5

•Baseband Spectrum
- 1 - 1 - 2 - 2 - 3

0 5 0 5 0 - 6 - 4 - 2 0 2 4 6 8

Sub-carrier generation
s (t ) = Ac ∑ x n f (t − nTs ) cos(ω c t ) − Ac ∑ y n f (t − nTs ) sin(ω c t )
−∞ −∞ ∞ ∞

Ac peak signal value x n and y n information bits (0, 1 or -1) f (t ) normalized baseband bit shape function ω c subcarrier frequency ASK: BPSK: x n = 1 or 0 x n = 1 or - 1 yn = 0 yn = 0

QPSK: x n = 1 or - 1 y n = 1 or - 1

If f(t) represents a rectangular bit shape, the PSD of the complex envelope of MPSK is sin(πfTS ) 2 P ( f ) = Ac TS ( ) , where TS is the symbol time. πfTS The 3dB bandwidth of BPSK and QPSK are both 0.88R if they have the same symbol rate R. Each symbol in QPSK represents 2 bits, so the spectrum efficiency is doubled.

4-subcarrier BPSK composite signal
T R A N S M IT 5 0 0 0 (m w ) 4 0 0 0 3 0 0 0 in t e n s it y 2 0 0 0 1 0 0 0 0 P u ls e -1 0 0 0 -2 0 0 0 -3 0 0 0 -4 0 0 0 -5 0 0 0 0 . 5 1 1 . 5 2 2 . 5 T im e 3 (p s ) 3 . 5 4 4 . 5 x 5 1 0
4

F IL T E R

O U T P U T

P U L S E

-->

IN T E N S IT Y

a ft e r c o m b i n e r

Waveform

T R A N S M IT h a n n e l N u m b e r= 4 5 it R a t e = 2 . 40 8 in t e n s it y G b /s n m (m w )

F IL T E R

T O T A L

S P E C T R A L

IN T E N S IT Y

h a n n e l W

a 5v e l e n g t h = 1 5 5 0 -1 0 -1 5 -2 0 -2 5 -3 0 -3 5 -4 0 -4 5 -3 0

P u ls e

Spectrum

-2 0

-1 0

0 F re q u e n c y (G H z )

1 0

2 0

3 0

Dual-drive MZ modulator and OSSB signal generation Implementation
Lightwave in 0o Microwave signal 90o Hybrid AC AC

90o

Bias DC

Lightwave out

Dual-drive MZ modulator and OSSB signal generation Theory
Modulator output

Eo (t ) =

A {cos[ω o t + φ1 (t )] − cos[ω ot + φ 2 (t )]} 2

φ1 , φ2 phase delay of the two arms
Set φ1 (t ) = γπ + βπ cos Ωt and φ 2 (t ) = βπ cos(Ωt + θ ) ,

Vdc DC bias of one arm, Vπ |V | β = ac optical modulation index. Vπ π 1 When γ = , and θ = , 2 2 E Eo (t ) = − i {J 0 ( βπ )[sin(ω o t ) + cos(ω o t )] + 2J1 ( βπ ) cos(ω o − Ω)t + 2J 2 ( βπ )...... 2

γ=

s

OSSB Spectrum
) in t e n s it y u m b e r = 4 = 2 . 4 8 G b / s0 W a v e le n g t h = 1 5 5 0 - 1 0 ( m - 2 0 - 3 0 - 4 0 u ls e - 5 0 - 6 0 - 7 0 - 8 0 - 9 0 - 4 0 - 3 0 - 2 0 - 1 0 0 F r e q u e n c y 1 0 ( G H 2 0 z ) 3 0 4 0 5 0 N w T R A N S M IT F IL T E R T O T A L S P E C T R A L IN T E N S IT Y b e fo r e F P n m

s

Nonlinear distortion of unlinearized modulator
s s

P
40

Generate CTB but no CSO CTB is proportional to the square of modulation index
2 0

20

0

0

-2 0

-2 0

-4 0

-4 0

-6 0

-6 0

-8 0

-8 0

-1 0 0 0 2 4 6 8 1 0 12 14

-1 0 0 0 2 4 6 8 1 0 1 2 1 4 1 6

Carrier suppression
s s

Increase modulation efficiency Reduce modulator-induced nonlinearity
FPI reflection FPI transmission

Signal in

FPI

Bias control Signal out

Carrier suppression
Before carrier suppression
TRANSMIT FILTER TOTAL SP ECTRAL INTENSITY before FP 0 0 th=1550 nm -10 -20 -20 -30 Pulse intensity (mw) -2 -30 Pulse intensity (mw) -40 -3 -50 -60 -70 -80 -90 -90 -40 -30 -20 -10 0 10 Frequency (GHz) 20 30 40 -6 -80 -60 -40 -20 0 20 40 60 80 -40 -30 -20 -10 0 10 Frequency (GHz) 20 30 40 -5 -80 -40 -50 -60 -70 ber=4 Gb/s 0 elength=1550 nm -10 TRANSMIT FILTER TOTAL SP ECTRAL INTENSITY after FP

FP filter

After carrier suppression

-1

amplitude

-4

TRANSMIT FILTER OUTPUT PULSE --> INTENSITY before FP 4000 1800 3500 1600 1400 Pulse intensity (mw) 1200 1000 800 600 1000 400 200 0 0.5 1 1.5 2 2.5 3 Time (ps ) 3.5 4 4.5 5 x 10
4

TRANSMIT FILTER OUTPUT PULSE --> INTENSITY after FP

3000 Pulse intensity (mw)

waveform

2500

2000

1500

500

0

0.5

1

1.5

2

2.5 3 Time (ps )

3.5

4

4.5

5 x 10
4

Optical fiber simulation model
Standard s ingle mode fiber Inline am p lifier (E D FA ) Standard s ingle mode fiber Inline am p lifier (E D FA )

Standard s ingle mode fiber

Pream plifier (E D FA )

F ib er p a th w ith o u t d isp ersio n co m p en sa tio n

Standard s ingle mode fiber

D ispersion C om pensa tion (fiber or grating)

Inline am p lifier (E D FA )

Standard s ingle mode fiber

D ispersion C om pensa tion (fiber or grating)

Pream plifier (E D FA )

F ib er p a th w ith d isp ersio n co m p en sa tio n

Optical fiber simulation model
s

Span length ranges from 40 to 80 km. 3 dB loss margin reserved for each span (If the dispersion compensation is implemented, the additional loss is 6dB) Attenuation of each span is compensated by optical amplification. Neglect nonlinearity of Dispersion Compensator SMF parameter: α=0.25 dB/km, n2=2.36e-20, Aeff = 71um2 , D= 18 ps/nm/km. Dispersion slope 0.093 ps/nm^2/km. PMD coefficient 0.1 or 0.5ps/sqrt(km) . Solve Nonlinear Schrodinger Equations, neglect SRS and SBS. Using Split-step Fourier method.

s s s

s s

Optical fiber simulation model
0 -1 0 -2 0 -3 0 -4 0 -5 0 -6 0 -7 0 -8 0 -9 0 -1 0 0 -2 0 -1 0 0 1 0 2 0 3 0 4 0

(a) sp ectru m b efor e th e o ptical fib er

0 -1 0 -2 0 -3 0 -4 0 -5 0 -6 0 -7 0 -8 0 -9 0 -1 0 0 -4 0

-3 0

-2 0

-1 0

0

1 0

2 0

3 0

4 0

5 0

(b) o ptical sp ectru m a fter 8 0 k m fibe r tra n sm ission Figu re 2 .1 2 op tical spe ctru m b efor e an d a fter 8 0 k m fib er tra n sm issio n, o ptical po w er is 3 dB m

Simulation model for receiver
WDM Demultiplexer Preamplifier EDFA optical detector RF coupler

Q calculation

Sychronization

LPF

Channel 1 RF ossilator (3.6GHz)

Q calculation

Sychronization

LPF

Channel 4 RF ossilator (17.5GHz)

Simulation model for receiver
s

WDM demultiplexer: 6th-order Butterworth filter, 30GHz bandwidth. EDFA preamplifier: fixed output 1dBm total Analytic formula to calculate ASE noise Photo-detection: square-law operation + low-pass filter.
-3 0 -4 0

s s s

-5 0

-6 0

-7 0

-8 0

-9 0

-1 0 0 -3 0 -2 0 -1 0 0 1 0 2 0

Simulation model for receiver
s s

High pass filter: reduce DC component after O/E conversion Carrier recovery: Mth Power loop for MPSK carrier recovery
Input: s(t ) = A cos(2πf c t + θ k + θ ) , for kTS ≤ t ≤ (k + 1)TS , TS symbol time

θ k = 0,

2π 2π 2π 2π ,2 ,3 ,.....,(M − 1) M M M M

θ : phase delay due to the transmission and transmitter bias
s M (t ) = AM cos(2πMfc t + Mθ ) + higher order harmonics Select the first term using a bandpass filter, divide the frequency by M C (t ) = K cos(2πf ct + θ )

2nd power loop for BPSK carrier recovery
An example
(a)

Bandpass filter

(b)

mixer

(c)

narrow band filter

(d)

Composite RF signal Channel selection

frequency didvider

(e)

Select 2nd order harmonic

recovered subcarrier

4

2

(a) (b) (c)

0

-2

-4

(d)
-6

-8 0 .5 1 1 .5 2 2 .5 3 3 .5 4 x 10
-9

(e)

Demodulation
Spectrum
0.1
0

Mixer output
Waveform
C ha n ne l W a ve le ng th 1 5 5 0 n m C a rrie r fre q u e nc y=3 .6 0 3 8 G H z 0 .1 2 0 .0 8 0 .0 6 0 .0 4 0.1

Eyediagram

-1 0

-2 0

0 .0 8 0 .0 2

-3 0

0 -0 .0 2 -0 .0 4

0 .0 6

-4 0

0 .0 4

-5 0

0 .0 2 -0 .0 6

-6 0 -8 -6 -4 -2 0 2 4 6

-0 .0 8 0.5 1 1 .5 2 2 .5 3 3 .5 4 4 .5 5 x 10
4

0 2 00 400 60 0 800 10 00 1200 140 0 1600 180 0

Baseband filter output
Spectrum
-6 0 0 .1 2 0.1 -7 0 0.1 0 .0 8 -8 0 0 .0 8 0 .0 6 -9 0 0 .0 6 0 .0 4

Waveform
0 .1 2

Eyediagram

-1 0 0

0 .0 4

0 .0 2 -1 1 0 0 -1 2 0 -4 -3 -2 -1 0 1 2 3 4 0.5 1 1.5 2 2 .5 3 3 .5 4 4 .5 5 x 10
4

0 .0 2

0 200 4 00 600 800 1 000 120 0 1400 1 600 180 0

PMD-induced polarization walk-off
between carrier and sub-carriers

PMD definition: ∆ τ = ∆ ω
∆ τ DGD in seconds, ∆ θ relative wave vector rotation in radians ∆ ω optical frequency change that produced the rotation, in radians/seconds

∆θ

Consequence:
Decrease the beating efficiency between carrier and sub-carriers by cos( ∆θ )

PMD-induced waveform distortion
• In a Gaussian pulse IMDD system, the limitation from PMD is estimated by 0.020 B2 L ≈ B: data rate, L: maximum transmission distance ( DGD)2 • For SCM system, assume the pulse width is the period of the sinusoid sub-carriers at 12GHz or 18GHz • With DGD of 0.5ps/ km L = 240km and 550km for 12GHz and 18GHz sub-carriers • With DGD of 0.1ps/ km L = 6000km and 13000km for 12GHz and 18GHz sub-carriers
12000

10000

L(km)

8000

6000

4000

2000

0 .1

0 .1 5

0 .2

0 .2 5

0 .3

0 .3 5

0 .4

0 .4 5

0 .5

DGD (ps/sqrt(km))

Analytic estimation of receiver sensitivity
s

Approximations:
s s s s s

All noises considered additive with Gaussian statistics Signal-ASE beat noise dominant 5dB EDFA noise figure Neglect waveform distortion Linear approximation for MZ modulator

s

Calculated receiver sensitivity
s s s s

-31dBm for 4-subcarrier BPSK, 10Gb/s total capacity -34dBm for 2-subcarrier QPSK , 10Gb/s total capacity -46dBm for single channel IMDD OC48, 2.5Gb/s capacity -40dBm for single channel IMDD OC192, 10Gb/s capacity

4-subcarrier BPSK, self-coherent detection
(2.5Gb/s per sub-carrier,10Gb/s total capacity)
Optimal receiver bandwidth 0.7 ξ datarate
-1 8

-2 0

Sensitivity (dBm)

-2 2

-2 4

-2 6

-2 8

-3 0

-3 2 0 .2

0 .3

0 .4

0 .5

0 .6

0 .7

0 .8

0 .9

1

Bandwidth/datarate

4-subcarrier BPSK, self-coherent detection
(2.5Gb/s per sub-carrier,10Gb/s total capacity) RF channel spacing should be larger than 4.2 GHz
-1 2 -1 4 -1 6 -1 8 -2 0 -2 2 -2 4 -2 6 -2 8 -3 0 -3 2 2 .5

Sensitivity (dBm)

3

3 .5

4

4 .5 x 10

5
9

RF channel spacing (Hz)

4-subcarrier BPSK, self-coherent detection
(2.5Gb/s per sub-carrier,10Gb/s total capacity) Lowest frequency sub-carrier should be larger than 2.6 GHz
10 5

Receiver Sensitivity(dBm)

640km

0 -5 -10 -15 -20 -25 -30 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 x 10 3.8
9

560km

480km

Subcarrier 1 Frequency(Hz)

4-subcarrier BPSK, self-coherent detection
(2.5Gb/s per sub-carrier,10Gb/s total capacity) Carrier suppression can improve the sensitivity on a roughly dB-per-dB base
-12 -14 -16 -18

Sensitivity (dBm)

-20 -22 -24

No suppression
-26 -28 -30 -32 0.05

with 5dB suppression
0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

OMI

4-subcarrier BPSK, self-coherent detection
(2.5Gb/s per sub-carrier,10Gb/s total capacity)
0 km
-10 -15

500 km

-10

Sensitivity (dBm)

-20

-25

Sensitivity (dBm)

increase OMI

-15

increase OMI

-20

-30

-35 -30

-25

-20

-15

-10

-5

0

-25 -25

-20

-15

-10

-5

0

Suppression ratio (dB)

Suppression ratio (dB)

420 km
-14 -16

-18

increase OMI

Sensitivity (dBm)

-20

-22

-24

-26

-28 -30

-25

-20

-15

-10

-5

0

Suppression ratio (dB)

4 BPSK subcarrier SCM system results
PMD DC OMI OP dB m RFM I Freq1 L: 1 wavelength Yes yes yes yes yes yes yes yes no no no no no no no no 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 5 5 3 3 0 0 -3 -3 5 5 3 3 0 0 -3 -3 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 600 600 560 400 920 680 640 520 L: 4 wavelength 450 300 350 400 350 250 250 200 200 200 250 250 350 350 350 250

ps km
0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps

4 BPSK subcarrier SCM system results
PMD DC OMI OP dBm RFMI Freq1 L: 1 wavelength 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 5 5 3 3 0 0 -3 -3 5 5 3 3 0 0 -3 -3 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 0.9 0.9 1.15 1.35 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 1.12 1.05 1.05 0.9 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 500 440 440 360 440 360 360 280 L: 4 wavelength 350 350 350 350 250 250 250 150 200 200 250 250 300 250 250 200

ps km
0.5ps yes 0.5ps yes 0.5ps yes 0.5ps yes 0.5ps yes 0.5ps yes 0.5ps yes 0.5ps yes 0.5ps no 0.5ps no 0.5ps No 0.5ps No 0.5ps No 0.5ps No 0.5ps No 0.5ps No

2-subcarrier QPSK, self-coherent detection
(5Gb/s per sub-carrier,10Gb/s total capacity)

Optical spectrum
Cha nne l Numbe r=2 0 Bit Ra te =2.48 Gb/s Cha nne l Wa ve le ngth=1550 nm -20 0.3 0.25

Eye diagram
Channel Number=2 Channel Wavelength=1000000000 nm Number of s amples /bit=64

-40

0.2

-60 0.15 -80 0.1 -100 0.05 -120

-140 -60 -40 -20 0 20 40 60

0 200 400 600 800 1000 1200 1400 1600 1800

2-subcarrier QPSK, self-coherent detection
(5Gb/s per sub-carrier,10Gb/s total capacity)
PMD 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps 0.1ps DC Yes Yes Yes Yes Yes Yes Yes Yes No No No No No No No No OMI 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 OP(dBm) 5 5 3 3 0 0 -3 -3 5 5 3 3 0 0 -3 -3 RFMI 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 Freq1 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 L 1100 950 1200 900 750 550 500 350 400 400 450 450 250 250 250 250

2-subcarrier QPSK, self-coherent detection
(5Gb/s per sub-carrier,10Gb/s total capacity)
PMD 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps 0.5ps DC Yes Yes yes yes yes yes yes yes no no no no no no no no OMI 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 0.3 0.4 OP(dBm) 5 5 3 3 0 0 -3 -3 5 5 3 3 0 0 -3 -3 RFMI 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 Freq1 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 L 750 650 700 500 500 350 350 250 400 400 450 450 250 250 250 250

SCM system, direct-detection
Using narrow-band optical filters

Narrowband optical filter

photodiode

LPF

Bit synchronization

Q

Narrowband optical filter WDM Demultiplexer Preamplifier EDFA

photodiode

LPF

Bit synchronization

Q

Narrowband optical filter

photodiode

LPF

Bit synchronization

Q

Narrowband optical filter

photodiode

LPF

Bit synchronization

Q

SCM system, direct-detection
Using narrow-band optical filters
Before baseband filter
0
0.5

-1 0

0.4

-2 0
0.3

-3 0
0.2

-4 0
0.1

-5 0
0

-6 0
200 400 600 800 1000 1200 1400 1600 1800

-2 0

-1 0

0

10

20

30

after baseband filter
0 .4

-10

0 .3 5 0 .3

C ha nne l Num b e r=4 C ha nne l W a ve le ng th=1 0 0 0 0 0 0 0 0 0 nm Num b e r o f s a m p le s /b it=6 4

-20

0 .2 5 0 .2 0 .1 5

-30

-40

0 .1 0 .0 5

-50

0 -0 .0 5

-60
-0 .1 200 400 600 800 1000 1200 1400 1600 1800

-70

-15

-10

-5

0

5

10

15

20

After narrowband optical filter

Impact of optical filter bandwidth
-2 8

-2 9

Receiver sensitivity (dBm)

-3 0

-3 1

-3 2

-3 3

-3 4

1

1 .5

2

2 .5

3

3 .5

4

4 .5

5

Optical filter bandwidth (GHz)

SCM system, direct-detection
Using narrow-band optical filters

-5

10 5

-10

Receiver Sensitivity(dB)

Receiver Sensitivity(dB)

0 -5 -10 -15 -20 -25 -30 -35

-15

-20

increase OMI

P=-3dBm 0dBm

5dBm

3dBm

-25

-30

-35 -45

0

200

400

600

800

1000

1200

-40

-35

-30

-25

-20

-15

-10

Carrier Suppression(dB)

Fiber Length(km)

Maximum transmission distance
direct-detected SCM system

DC Yes Yes Yes Yes No No no No

OMI 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3

OP 3 0 -3 -6 3 0 -3 -6

RFMI 1111 1111 1111 1111 1111 1111 1111 1111

L 50 200 250 250 250 550 500 350

OC192 TDM system using NRZ modulation

DC Yes Yes Yes Yes No No No No

OMI 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

OP (dBm) 3 0 -3 -6 3 0 -3 -6

Length (km) 950 1100 800 500 100 100 100 100

Experiments for one wavelength four subcarriers BPSK SCM system
3 .6 G H z

L a ser
D ata gen erato r 8 .3 G H z P ower S p litter P o w er co m b in
00

13GHz

a m plifier

90 0

2 .4 8 8 G b /s

DC

B ias

1 7 .5 G H z

BER tester

S cope
3 .6 G H z

LPF
8 .3 G H z P ower S p litter

ED FA P ost-a m p F iber D etector P re-a m p ED FA P re-a m p.

LPF
13GHz

LPF
1 7 .5 G H z

LPF

OSSB
Normalized Optical spectral density (dB)
0 -5 -10 -15 -20 -25 -30 -35 -50 -40 -30 -20 -10 0 10 20 30 40

Frequency ( GHz)

Detected composite signal RF spectrum
-2 0 -2 5

In ten sity (d B m )

-3 0 -3 5 -4 0 -4 5 -5 0 -5 5 0 2 4 6 8 10 12 14 16 18 20 22

F r eq u en cy (G H z )

Measured eye diagrams
back-to-back and over 75km SMF
fc=8.3GHz, back-to-back, P=-23.5 dBm c=8.3GHz, over fiber, P =-23 dBm f fc=13GHz, back-to-back, P =-27.6 dBm fc=13GHz, over fiber, P =-24 dBm

fc=3.6GHz, back-to-back, P =-24.9 dBm fc=3.6GHz, over fiber, P =-22.6 dBm

fc=17.5GHz, back-to-back, P =22.7 dBm

fc=17.5GHz, over fiber, P =-21.5 dBm

Measured BER
back-to-back (stars) and over 75km SMF (circles)
10-3 10-4 10-5 BER BER 10-6 10-7 10-8 10-9 10-10 -34 * back/back o over 75km SMF -32 -30 -28 -26 Optical power ( dBm) Channel #3 ( fc = 13GHz) -24 -22 Channel #1 ( fc = 3.6GHz) 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10
-10

Channel #2 ( fc = 8.3GHz)

* back/back o over 75km SMF -34 -32 -30 -28 Optical power ( dBm) Channel #4 ( fc = 17.5GHz) -26 -24

-36

10 10 10 10 BER 10 10 10

-3 -4 -5 -6 -7 -8 -9

10 -3 10 -4 10 -5 BER 10 -6 10 -7 10 -8

* back/back o over 75km SMF -34 -32 -30 -28 Optical power ( dBm) -26 -24

10 -9 10 -10 -34

* back/back o over 75km SMF -32 -30 -28 -26 Optical power ( dBm) -24 -22

10-10 -36

Effects of carrier suppresion
-2 9 n o carrier su ppression

R e ce ived se n sitiv ity ( B m ) d

-3 1

w ith carrier su pp ressio n

-3 3

-3 5

-3 7

-3 9 0 2 4 6 8

R F p o w e r to m o d u la to r (d B m )

Effect of channel spacing
-26 -27

Receiver sensitivity (dBm)

-28 -29 -30 -31 -32 -33 -34 -35 4.4 4.6 4.8 5 5.2 5.4 5.6 5.8

FR channel separation (GHz)

Comparison between SCM and TDM
S M F E q u iva le n t F ib er L e n g th ( k m )
-5 -1 0 -1 5 -2 0 -2 5 -3 0 -3 5
SCM TD M

0

20

40

60

80

100

120

140

160

180

200

R e c eiv er s e n sitivity (dB m )

0

340

680

1020

1360

1700

2040

2380

2720

3060

3400

A c c u m u la te d d is p ersio n ( ps/n m )

Conclusion remarks
s s

Built a simulator for SCM/WDM systems Simulated multi-wavelength SCM systems: 4-subcarrier BPSK, 2subcarrier QPSK and 4-subcarrier ASK Optimized system parameters BPSK format is recommended for 300km to 350 km transmission without dispersion compensation. QPSK format is recommended for up to 750 km transmission with dispersion compensation and 450km without dispersion compensation. ASK system is not recommended because of the stringent requirement of optical filters. Experimentally measured the performance of single-wavelength 4subcarrier BPSK system

s s

s

s

s

Furture work
s s s s s

Multi-wavelength SCM test bed Experimental investigation of QPSK and M-ary Impact of Raman amplification on SCM systems Single-sideband RF modulation Detailed PMD analysis

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