In technical terms, dispersion in optica.ppt

In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber. It causes pulses of light to spread out over time, leading to signal degradation and limiting the transmission capacity of the fiber.8 2023In technical terms, dispersion in optical fiber refers to the phenomenon where different wavelengths of light experience varying velocities as they travel through the fiber.

1. Fujitsu1
New functionalities for advanced optical
interfaces (Dispersion compensation)
Kazuo Yamane
Photonic systems development dept.

2. Fujitsu2
Outline
Chromatic dispersion effect
Dispersion compensating techniques
Optimization of residual dispersion or its map
PMD compensation
Conclusions

3. Fujitsu3
Signal distortion due to chromatic dispersion
Spectrum broadening
Difference in group velocity
Wavelength
Group velocity
Δλ
1
Time
10
Original signal
Time
Transmitter output
Time
Receiver input
Time
111
Regenerated signal
Wavelength
Optical spectrum
Δλ
Pulse broadening
(Waveform distortion)
Optical fiber

4. Fujitsu4
Waveform distortion due to fiber non-linearity
Transmitter out Received waveform
Low optical power High optical power
High power
intensity
Frequency
chirp
Refractive
index change
Waveform distortion
due to chromatic
dispersion
Optical fiber
Spectrum
broadening

5. Fujitsu5
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

6. Fujitsu6
Fiber#1
DC allocations and dispersion maps
DCDC
Fiber#2
Distance
[km]
R.D. [ps/nm]
Fiber#1
DC DC
Fiber#2
Fiber#1
DCDC
Fiber#2
DC
Distance
[km]
R.D. [ps/nm]
Distance
[km]
R.D. [ps/nm]
Post-
comp.
Pre-comp.
Post-&
Pre-
comp.
+
-
-
-
+
+
0
0
0

7. Fujitsu7
Residual dispersion and tolerance of receiver
Distance [km]
R.D. [ps/nm]
Dispersion
tolerance
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. [ps/nm]
+
0
Penalty [dB]
Longer wavelength
Shorter wavelength
Center wavelength
Allowable
penalty

8. Fujitsu8
CS-RZ Optical duobinaryNRZ RZ
Optical power (dBm)
Wavelength (nm)
0
-20
-40
1542 1545 1548
0
-20
-40
1542 1545 1548
0
-20
-40
1542 1545 15481542 1545 1548
0
-20
-40
Wavelength (nm) Wavelength (nm) Wavelength (nm)
Chromatic dispersion tolerance
Fibre 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

9. Fujitsu9
A past field experiment example
Berlin Darmstadt
Link 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

10. Fujitsu10
Dispersion maps and waveforms in the trial
-2000
-1500
-1000
-500
0
500
1000
1500
2000
Dispersion (ps/nm)
Channel 1
Channel 2
Channel 3
Channel 4
-2000
-1500
-1000
-500
0
500
1000
1500
2000
0
Distance (km)
Dispersion (ps/nm)
Before optimization
After optimization
800600400200
0
Distance (km)
800600400200
Channel 1
Channel 1
(Before)
(After)

11. Fujitsu11
l
i
Provisioning
l
1
l
40Tx #40
Tx #1
l
2
Tx #2
Rx #1
Rx #2
Rx #40
Automatic dispersion compensation example
VDC VDC
Dispersion
Monitor
DC
Dispersion compensator
(fixed or variable)
Provisioning
&
Tracking
Collimating lens
Line-focusing
lens
Glass
plate
Focusing
lens
3-Dimensional Mirror
Optical circulator
Variable
x-axis
VIPA : Virtually Imaged Phased Array
VIPA variable dispersion compensator
DC
D
C> 0
D
C< 0

12. Fujitsu12
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!!

13. Fujitsu13
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
Dt
D t : Differential Group Delay (DGD)
Dt

14. Fujitsu14
D t
1 D t
4D t
2 D t
3
D t
n
Mode-coupling at random locations with random strength
Higher-order PMD
…
Frequency of occurrence
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

15. Fujitsu15
Automatic PMD compensation
PMD characteristic changes slowlydue 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
Distortion
analyzer
Control
algorithm
PMD
comp.
device #3
PMD
comp.
device #2
PMD
comp.
device #1
O/E
module

16. Fujitsu16
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.