fujitsu1 new functionalities for advanced optical interfaces (dispersion compensation) kazuo yamane...
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New functionalities for advanced optical interfaces (Dispersion compensation)
Kazuo YamanePhotonic systems development dept.
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Outline
Chromatic dispersion effect Dispersion compensating techniques Optimization of residual dispersion or its map PMD compensation Conclusions
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Signal distortion due to chromatic dispersion
Spectrum broadening
Difference in group velocity
Wavelength
Gro
up
vel
oci
ty
Δλ
1
Time
1 0Original signal
Time
Transmitter output
Time
Receiver input
Time
111Regenerated signal
Wavelength
Optical spectrum
Δλ
Pulse broadening(Waveform distortion)
Optical fiber
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Waveform distortion due to fiber non-linearity
Transmitter out Received waveform
Low optical power High optical power
High power intensity
Frequencychirp
Refractive index change
Waveform distortion due to chromatic dispersion
Optical fiber
Spectrumbroadening
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After fiber transmission
40 Gb/s optical signal
Transmitter output
25 ps
Transmission fiber
Positive dispersion(Negative dispersion)
+Dispersion compensating fiber (DCF)
After dispersion comp.
Negative dispersion (Positive dispersion)
Longer wavelength
Slow (Fast)
Shorter wavelength
Fast (Slow)
Longer wavelength
Fast (Slow)
Shorter wavelength
Slow (Fast)
Dispersion compensation example
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Fiber#1
DC allocations and dispersion maps
DCDC
Fiber#2
Distance [km]
R.D
. [p
s/n
m]
Fiber#1
DC DC
Fiber#2
Fiber#1
DCDC
Fiber#2
DC
Distance [km]
R.D
. [p
s/n
m]
Distance [km]
R.D
. [p
s/n
m]
Post-comp.
Pre-comp.
Post- & Pre-
comp.
+
-
-
-
+
+
0
0
0
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Residual dispersion and tolerance of receiver
Distance [km]
R.D
. [p
s/n
m]
Dispersiontolerance
of receiver
-
+
Need to consider the variation of tolerance due to characteristics of transmitter, fibre non-linear effects and dispersion map.Even if residual dispersion values are same, the received waveforms are different, affected by these parameters.
Parameters affecting to the tolerance - Signal bit rate - Channel counts and spacing - Distance or number of spans - Fibre type - Fibre input power - Pre-chirping of transmitter - Modulation scheme of transmitter - DC allocation / value
-
R.D
. [p
s/n
m]
+
0
Penalty [dB]
Longer wavelength
Shorter wavelength
Center wavelength
Allowable penalty
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CS-RZ Optical duobinaryNRZ RZ
Opt
ical
pow
er (
dBm
)
Wavelength (nm)
0
-20
-40
1542 1545 1548
0
-20
-40
1542 1545 1548
0
-20
-40
1542 1545 1548 1542 1545 1548
0
-20
-40
Wavelength (nm) Wavelength (nm) Wavelength (nm)
Chromatic dispersion toleranceFibre non-linear tolerance (Maximum input power)Spectral tolerance (Degradation due to filter narrowing)
108 GHz 180 GHz 165 GHz 70 GHz
Now evaluating transmission performance
Comparison of 40Gbit/s modulation schemes
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A past field experiment example
Berlin DarmstadtLink for field trial
-400 ps/nm +900 ps/nm
E/OO/E
10Gbit/s 750km WDM field trial between Berlin and Darmstadt (Ref.: OFC/IOOC’99, Technical Digest TuQ2, A. Ehrhardt, et.al.)
Post-amplifier
Post-amplifier
Pre-amplifier
Pre-amplifier
E/OO/E
After optimization
Before Optimization
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Dispersion maps and waveforms in the trial
-2000
-1500
-1000
-500
0
500
1000
1500
2000
Dis
per
sio
n (
ps/
nm
)
Channel 1
Channel 2
Channel 3
Channel 4
-2000
-1500
-1000
-500
0
500
1000
1500
2000
0Distance (km)
Dis
per
sio
n (
ps/
nm
)
Before optimization
After optimization
800600400200
0Distance (km)
800600400200
Channel 1Channel 1
(Before)(After)
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i
Provisioning1
40 Tx #40
Tx #1
2 Tx #2
Rx #1
Rx #2
Rx #40
Automatic dispersion compensation example
VDC VDC
DispersionMonitor
DispersionMonitor
DC
Dispersion compensator (fixed or variable)
Provisioning&
Tracking
Collimating lens
Line-focusing lens
Glass plate
Focusing lens
3-Dimensional Mirror
Optical circulator
Variablex-axis
VIPA : Virtually Imaged Phased Array
VIPA variable dispersion compensator
DC
DC > 0
DC < 0
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Dispersion compensation trend
Photonic network
Manage dispersion or residual dispersion (dispersion map) !!
NE
NE
NE
NE
NE
Transmitter / Receiver
Adjust parameters including residual
dispersion to optimum!!
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Polarization Mode Dispersion (PMD)
- Well defined, frequency independent eigenstates
- Deterministic, frequency independent Differential Group Delay (DGD)
- DGD scales linearity with fiber length
1st-order PMD
Ideal Practical
Core
Cladding
Cross-section of optical fiber
Fast axis
Slow axis
Fast
Slow
Differential Group Delay (DGD)
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1 42
3n
Mode-coupling at random locations with random strength
Higher-order PMD
…
Fre
qu
enc
y o
f o
ccu
rren
ce
Instantaneous DGD (ps)
Maxwellian distribution of the instantaneous DGD
PMD 3.5PMD
Prob.(DGD>3.5xPMD) =10-6 = 32 sec/year
Prob.(DGD>3xPMD) = 4x10-5 = 21 min/year
-Frequency dependence of DGD
-Statistically varying due to environmental fluctuations
-Fiber PMD unit: ps/ km
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Automatic PMD compensation
PMD characteristic changes slowly due to “normal” environmental fluctuations (e.g. temperature)
But, fast change due to e.g. fiber touching
High-speed PMD compensation device & Intelligent control algorithm
PMD compensation scheme in receiver
Before PMD comp.
After PMD comp.
40Gb/s waveforms
Distortionanalyzer
Controlalgorithm
PMDcomp.
device #3
PMDcomp.
device #2
PMDcomp.
device #1
O/Emodule
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Conclusions
In fibre optical high bit rate (such as 10G or 40G bit/s) long-haul transmission systems, dispersion compensation is one of the most important items to be considered for design.
Management or optimization of residual dispersion are required for photonic networks, i.e., for fibres, repeaters and optical interfaces.
PMD compensation is also required especially for 40Gbit/s or higher bit rate long-haul systems.