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www.viewegteubner.de
Vieweg+TeubnerPLUS
Additional information to media of Vieweg+Teubner Verlags
Elements of optical networking
Megabit and Gigabit and Terrabit and ???
by Prof. Dr. V. Brückner
1. The optical channel - DWDM
2. Limits by attenuation
3. Limits by dispersion
Megabit and Gigabit and Terrabit and ???
kB/s
MB/s
GB/s1 ms1 µs1 ns
Digital Bit pattern
transmitter
TB/s
I1
I2
I3
about 40 channels
1 000 01 1 1
Dense Wavelength Division Multiplexing(DWDM)
Bit duration
DWDM: the single optical channel:
The optical channels(wavelength consideration)
frequency
f0
Δf
100%
50%
wavelength
λ0
Δλ Line width
wavelength
frequency
f0
wavelength
λ0
The optical channels(wavelength consideration)
DWDM: the single optical channel:
Δλ≈1 pm line width
wavelength
3 optical channels:
frequency
100 GHz 100 GHz195.8 THz195.7 THz 195.9 THz
(193.1 + n.0.1) THz
ITU-T G.694.1for 100 GHz:
f
c f
cf
f
c
2
2
at λ = 1531.12 nm and Δf = 100 GHz -> Δλ = 0.75 nm
wavelength
1531.12 nm1530.37 nm 1531.87 nm
0.75 nm 0.75 nm
channel spacing
Requirements to wavelength stability of lasers: ±2.5% (±0.02 nm)!!!!!
The optical channels(wavelength consideration)
3 optical channels + modulation:
wavelength
1531.12 nm1530.37 nm 1531.87 nm
0.75 nm 0.75 nm
channel spacing
The optical channels(modulation)
Optical Time Division Multiplexing(OTDM)
Principle:Shuffling in time
(different run times in glass fibers)
3 optical channels + modulation:
wavelength
1531.12 nm1530.37 nm 1531.87 nm
0.75 nm 0.75 nm
channel spacing
The optical channels(modulation)
Equal length of time slots:Synchronous digital Hierarchie
(SDH)
Flexible length of time slots :Asynchronous Transfer Modus
(ATM)
STM level Bit rate
STM-256 39813,12 MBit/s
STM- 64 9953,28 MBit/s
STM- 16 2488,32 MBit/s
STM- 4 622,08 MBit/s
STM- 1 155,52 MBit/s
Synchron Transport Moduls:
fiber
1
n MUX DEMUX
1
n
WDM
OTDM with WDM:
The optical channels(modulation)
Principle :Shuffling in time
e.g. for STM-256 (40 GB/s)
S1 : 1 , τ1 < 10 ps
S2 : 1 , τ1 < 10 ps
Sm: 1 , τ1 < 10 ps
.
.
. t
m time slots a 25 ps = 1/40GBps
. . .
S1 S2 Sm
τ1 τ1 τ1
Principle:Generation of a frame of m time slots,
in total 40 GB/s (40 GBps)
Transmission capacity n * 40 GB/s
3 optical channels + modulation:
wavelength
1531.12 nm1530.37 nm 1531.87 nm
0.75 nm 0.75 nm
40 GB/s ~ fM = 40 GHz (0.3 nm)
Modulation with 40 GB/s (STM-256):
channel spacing
safety clearance
Safety clearance: 0.15 nm
The optical channels(modulation)
Resulting spectrum: Side bands f0 ± fM
Optical channels: scaling
wavelength
Present time: 40 channels - about 30 nm (40 GBps) = 1.6 TBps
1531.12 nm1501.87 nm
future: 80 channels - about 60 nm (40 GBps) = 3.2 TBps
160 channels - about 120 nm ?? (40 GBps) = 6.4 TBps
320 channels - about 240 nm ???? (40 GBps) = 12.8 TBps
The optical channels(wavelength + modulation)
Optical channels – conclusions:
or: 40 channels - about 30 nm (40 GBps) = 1.6 TBps
or: 80 channels - about 60 nm (20 GBps) = 1.6 TBps
or: 20 channels - about 15 nm (80 GBps) = 1.6 TBps
either: 10 channels - about 7.5 nm (160 GBps) = 1.6 TBps
Transfer of a data rate of 1.6 TBps:
Which way is better? Which problems arise?
The optical channels(wavelength + modulation)
Problem: low channel number -> higher channel distance -> technically less complicatedhigher bit rate -> shorter time slots -> technically more complicated (Dispersion)
Problem: lower bit rate -> less dispersion influence -> technically less complicatedhigher channel number -> shorter channel distance -> techncally more complicated (demultiplexing)
or
laser
modulator
MUXWDMDWDM
glass fiber
core9 µm
cladding125 µm
losses - attenuation
The optical channels(limits by attenuation)
laser
modulator
MUX
fiber The fiber:power in fibers
P0
z
P
100%
50%
physics: power engineering: level
kzePzP 0)(
W, mW dB, dBm
)1
log(10mW
Pp
mWdBm
)log(10in
outdB
P
Pa
p0
z
p
-3dB
attenuation in fibers (α): losses per kilometer (dB/km)
The optical channels(limits by attenuation)
700 800 900 1000 1100 1200 1300 1400 1500 1600 1700Wavelength [nm]
0,1
1
10
loss
es [
dB
/km
] Rayleigh scattering
OH absorption
standard SMF
AllWaveTM
Best values: 0.2 dB/km at 1500 nm
IR absorption
Si
O
OO
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
2nd 3d LS
DWDM: 40 channels, 50 GHz distance
H
H
vibrations
The optical channels(limits by attenuation)
700 800 900 1000 1100 1200 1300 1400 1500 1600 1700wavelength [nm]
0,1
1
10
loss
es [
dB
/km
]
3d LS
DWDM: 40 chanals, 50 GHz
200 nm
Max. bandwidth in SSMF: 200 nm or 25 THz
The optical channels(limits by attenuation)
laser
modulator
MUX
fiber
The fiber:amplification
Rec S T A
LD
opticaldata
opticaldata
electricaldata
ID
I0
3R regeneration: amplification (Re-amplification), clock reinstallation (Re-timing) and pulse formation (Re-shaping)Classical way:
>>
The optical channels(limits by attenuation)
3R regeneration: amplification (Re-amplification), clock reinstallation (Re-timing) and pulse formation (Re-shaping) optical way:
Optical amplification: Erbium-doped fiber amplifier EDFA
Raman amplifier ROASemiconductor optical amplifier SOA
no Re-timing, no Re-shaping!!!
The fiber:amplificationlaser
modulator
MUX
fiber
>>
The optical channels(limits by attenuation)
kBit/s
MBit/s
GBit/s
1 ns
Bit pattern
Laser
Modulator
DWDM
The optical channels(limits by dispersion)
idealrect pulse
time
t 2 1.975 5
r t( )
t
realrect pulse
, 3, 5, 7 usw.
time
t 2 1.975 5
g t( )
t
time
real, Gaussianpulse after
a short glass fiber
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
time
broadened, Gauss-shaped pulse after dispersion in a
long glass fiber
p
dis
Influence of dispersion to a single Bit
dis > p
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
t 2 1.975 5
g t( )
t
The optical channels(limits by dispersion)
L0 = 0 L1 > L0 L2 > L1 L3 > L2
2 Bits 2 Bits 2 Bits ??
1 oder 2 Bits?????
time time time time
The optical channels(limits by dispersion)
Dispersion
Modal dispersion (MMF)
Chromatic Dispersion (MMF and SMF)
Material dispersion (MMF and SMF)
Waveguide dispersion (SMF)
Polarization mode dispersion (SMF) Dep
enden
t on
The optical channels(limits by dispersion)
modal dispersionModal Dispersion in SI-Fibers (MMF)
Different runtime Δtg for all paths, because of different paths ways
Δtg
The optical channels(limits by dispersion)
modal dispersionmodal dispersion in GI-Fibers (MMF)
Nearly the same runtime for all paths, because different paths and velocities are compensated
The optical channels(limits by dispersion)
Chromatic Dispersion (CD)= Material Dispersion + Waveguide Dispersion
Different wavelengths in the LD-Spectrum have different transit times
Light sources are not monochromatic, but have a finite broad spectrum
t
t3t2t1
The optical channels(limits by dispersion)
P
Material dispersion
L
1
2
3 Selection of 3 wavelengths:3 > 2 > 1 thus n3 < n2 < n1 thus v3 > v2 > v1
3
2
1
Path difference
in Multi-Mode and Single-Mode fibers
Spectral width -> tg by different propagation speeds
n
λ
Dispersion
The optical channels(limits by dispersion)
tg by different propagation speedsin core and cladding (in SMF only)
L
d1= 9 µm
d2 = 5µm< d1
P
x
P
x
Situation: nK > nM thus vK < vM
Wave guide dispersion
The optical channels(limits by dispersion)
SMF DFF DSFindex
core core core
DChrom (ps/km*nm)
SMFDSF
DFF (µm)
chromatic dispersion
The optical channels(limits by dispersion)
bit pattern dispersion
dispersioncompensation
pulse broadening(overlap of Bits)
chromatic dispersion
The optical channels(limits by dispersion)
dispersion compensating fiber
5 km DCF 40 km SMF
Spleisses
40 km SMF5 km DCF
SMF
8 parts SMF + 1 part DCF
DCF
-300
Dps/km*nm
-200
-100
0
+100
1.1
(µm)
1.3 1.5 1.7
compensation:DCF
core
n
The optical channels(limits by dispersion)