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New functionalities for advanced optical interfaces ( Dispersion compensation). Kazuo Yamane Photonic systems development dept. Outline. Chromatic dispersion effect Dispersion compensating techniques Optimization of residual dispersion or its map PMD compensation Conclusions .

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New functionalities for advanced optical interfaces dispersion compensation l.jpg

New functionalities for advanced optical interfaces (Dispersion compensation)

Kazuo Yamane

Photonic systems development dept.

Fujitsu


Outline l.jpg

Outline

  • Chromatic dispersion effect

  • Dispersion compensating techniques

  • Optimization of residual dispersion or its map

  • PMD compensation

  • Conclusions

Fujitsu


Slide3 l.jpg

Signal distortion due to chromatic dispersion

Spectrum broadening

Optical spectrum

Δλ

Difference in group velocity

Wavelength

Pulse broadening

(Waveform distortion)

Transmitter output

Receiver input

Optical fiber

Time

Time

Group velocity

Original signal

Regenerated signal

1

1

1

1

0

1

Wavelength

Δλ

Time

Time

Fujitsu


Slide4 l.jpg

Waveform distortion due to fiber non-linearity

High power

intensity

Refractive index change

Frequency

chirp

Spectrum

broadening

Waveform distortion due to chromatic dispersion

Optical fiber

Low optical power

High optical power

Received waveform

Transmitter out

Fujitsu


Slide5 l.jpg

25 ps

Dispersion compensation example

Transmission fiber

Dispersion compensating fiber (DCF)

+

Positive dispersion

(Negative dispersion)

Negative dispersion

(Positive dispersion)

Longer wavelength

Slow(Fast)

Longer wavelength

Fast (Slow)

Shorter wavelength

Fast(Slow)

Slow (Fast)

Shorter wavelength

40 Gb/s optical signal

Transmitter output

After fiber transmission

After dispersion comp.

Fujitsu


Slide6 l.jpg

DC

DC

DC

DC

DC

DC

DC

DC allocations and dispersion maps

Post-comp.

+

Fiber#1

Fiber#2

0

R.D. [ps/nm]

Distance [km]

-

Pre-comp.

+

Fiber#1

Fiber#2

0

R.D. [ps/nm]

Distance [km]

-

Post- & Pre- comp.

+

Fiber#1

Fiber#2

0

R.D. [ps/nm]

Distance [km]

-

Fujitsu


Slide7 l.jpg

Residual dispersion and tolerance of receiver

Allowable penalty

+

+

Longer wavelength

Dispersion

tolerance

of receiver

Center wavelength

0

R.D. [ps/nm]

R.D. [ps/nm]

Shorter wavelength

-

-

Distance [km]

Penalty [dB]

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

Fujitsu


Slide8 l.jpg

0

0

0

0

-20

-20

-20

-20

Optical power (dBm)

-40

-40

-40

-40

1545

1545

1545

1545

1542

1542

1542

1542

1548

1548

1548

1548

Wavelength (nm)

Wavelength (nm)

Wavelength (nm)

Wavelength (nm)

Comparison of 40Gbit/s modulation schemes

NRZ

RZ

CS-RZ

Optical duobinary

108 GHz

180 GHz

165 GHz

70 GHz

Now evaluating transmission performance

Chromatic dispersion tolerance

Fibre non-linear tolerance (Maximum input power)

Spectral tolerance (Degradation due to filter narrowing)

Fujitsu


A past field experiment example l.jpg

A past field experiment example

  • 10Gbit/s 750km WDM field trial between Berlin and Darmstadt (Ref.: OFC/IOOC’99, Technical Digest TuQ2, A. Ehrhardt, et.al.)

Link for field trial

Berlin

Darmstadt

Before Optimization

E/O

O/E

Post-amplifier

Pre-amplifier

After optimization

+900 ps/nm

-400 ps/nm

O/E

E/O

Post-amplifier

Pre-amplifier

Fujitsu


Dispersion maps and waveforms in the trial l.jpg

2000

2000

1500

1500

1000

1000

500

500

0

0

-500

-500

-1000

-1000

-1500

-1500

-2000

-2000

Dispersion maps and waveforms in the trial

Before optimization

Dispersion (ps/nm)

Channel 1

Channel 3

Channel 2

Channel 4

0

800

400

600

200

Distance (km)

After optimization

Dispersion (ps/nm)

Channel 1

(Before)

Channel 1

(After)

0

800

400

600

200

Distance (km)

Fujitsu


Slide11 l.jpg

Automatic dispersion compensation example

Provisioning

&

Tracking

Provisioning

Rx #1

Tx #1

l1

Tx #2

l2

Rx #2

VDC

VDC

l40

Tx #40

Rx #40

DC

DC

li

Dispersion compensator

(fixed or variable)

Dispersion

Monitor

VIPA variable dispersion compensator

DC > 0

Line-focusing lens

Variable

x-axis

DC < 0

Optical circulator

Focusing lens

Collimating lens

Glass plate

3-Dimensional Mirror

VIPA : Virtually Imaged Phased Array

Fujitsu


Slide12 l.jpg

NE

NE

NE

NE

NE

Dispersion compensation trend

Photonic network

Manage dispersion or residual dispersion (dispersion map) !!

Transmitter / Receiver

Adjust parameters including residual dispersion to optimum!!

Fujitsu


Polarization mode dispersion pmd l.jpg

Polarization Mode Dispersion (PMD)

Cross-section of optical fiber

Practical

Ideal

Cladding

Fast axis

Core

Slow axis

1st-order PMD

Fast

Dt

Dt

Slow

D t : Differential Group Delay (DGD)

- Well defined, frequency independent eigenstates

- Deterministic, frequency independent Differential Group Delay (DGD)

- DGD scales linearity with fiber length

Fujitsu


Higher order pmd l.jpg

Higher-order PMD

D tn

D t4

D t1

D t2

D t3

Mode-coupling at random locations with random strength

Maxwellian distribution

of the instantaneous DGD

-Frequency dependence of DGD

-Statistically varying due to

environmental fluctuations

Frequency of occurrence

Prob.(DGD>3xPMD)

= 4x10-5 = 21 min/year

-Fiber PMD unit: ps/ km

Prob.(DGD>3.5xPMD)

=10-6 = 32 sec/year

PMD

3.5PMD

Instantaneous DGD (ps)

Fujitsu


Slide15 l.jpg

Automatic PMD compensation

PMD compensation scheme in receiver

40Gb/s waveforms

Before PMD comp.

PMD

comp.

device #1

PMD

comp.

device #2

PMD

comp.

device #3

O/E

module

Control

algorithm

Distortion

analyzer

After PMD comp.

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

Fujitsu


Conclusions l.jpg

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.

Fujitsu


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