DISPERSION COMPENSATION FIBRE

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Chromatic dispersion effectDispersion compensating techniquesOptimization of residual dispersion or its mapPMD compensationConclusions

Transcript of DISPERSION COMPENSATION FIBRE

New functionalities for advanced optical interfaces (Dispersion compensation)Kazuo YamanePhotonic systems development dept.

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Fujitsu

Outline

Chromatic dispersion effect Dispersion compensating techniques Optimization of residual dispersion or its map PMD compensation Conclusions

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Fujitsu

Signal distortion due to chromatic dispersionOptical spectrum Wavelength Transmitter output Spectrum broadening Difference in group velocity Pulse broadening (Waveform distortion) Optical fiberGroup velocity

Receiver input

Time Original signal

Time Regenerated signal

1

0

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1

1Time

Wavelength

Time

Waveform distortion due to fiber non-linearityHigh power intensity Refractive index change Frequency chirp Spectrum broadening Waveform distortion due to chromatic dispersion

Optical fiber

Low optical power

High optical power

Transmitter out4 Fujitsu

Received waveform

Dispersion compensation exampleTransmission fiber Dispersion compensating fiber (DCF)

Positive dispersion (Negative dispersion)Longer wavelength Shorter wavelength

+

Negative dispersion (Positive dispersion)Longer wavelength Shorter wavelength Fast (Slow) Slow (Fast)

Slow (Fast) Fast (Slow)

40 Gb/s optical signal

25 ps

Transmitter output5

After fiber transmissionFujitsu

After dispersion comp.

DC allocations and dispersion mapsR.D. [ps/nm]

Postcomp.

Fiber#1

Fiber#2

+

0

DC

DC

Distance [km]

+ R.D. [ps/nm]

Pre-comp.

Fiber#1

Fiber#2

0

DC

DC

Distance [km]

-

R.D. [ps/nm]

Post- & Precomp.

Fiber#1

Fiber#2

+

0

DC6

DC

DCFujitsu

Distance [km]

-

Residual dispersion and tolerance of receiverAllowable penalty + R.D. [ps/nm]Longer wavelength

+ R.D. [ps/nm] Distance [km] Penalty [dB]

0

Center wavelength Shorter wavelength

Dispersion tolerance of receiver

-

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 / value7 Fujitsu

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.

Comparison of 40Gbit/s modulation schemesNRZ RZ CS-RZ Optical duobinary

Optical power (dBm)

0

0

0

0

108 GHz-20-40 1542 1545 1548 -20 -40

180 GHz-20 -40 1545 1548 1542 1545

165 GHz-20 -40 1548 1542

70 GHz

1542

1545

1548

Wavelength (nm)

Wavelength (nm)

Wavelength (nm)

Wavelength (nm)

Now evaluating transmission performanceChromatic dispersion tolerance Fibre non-linear tolerance (Maximum input power) Spectral tolerance (Degradation due to filter narrowing)8 Fujitsu

A past field experiment example 10Gbit/s 750km WDM field trial between Berlin and Darmstadt (Ref.: OFC/IOOC99, Technical Digest TuQ2, A. Ehrhardt, et.al.)

BerlinBefore OptimizationO/E Post-amplifier

Link for field trial

Darmstadt

E/O Pre-amplifier

After optimization-400 ps/nm O/E Post-amplifier Pre-amplifier +900 ps/nm E/O

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Dispersion maps and waveforms in the trialDispersion (ps/nm)2000 1500 1000 500 0 -500 -1000 -1500 -20000 200 400 600 800 Channel 1 Channel 2 Channel 3 Channel 4

Before optimization

Distance (km)

Dispersion (ps/nm)

2000 1500 1000 500 0 -500 -1000 -1500 -20000 200 400 Channel 1 Channel 1 (Before) (After)

After optimization

600

800

Distance (km)10 Fujitsu

Automatic dispersion compensation examplel1 Tx #1 l2 Tx #2 ProvisioningVDC

Provisioning & TrackingVDC

Rx #1 Rx #2 Rx #40

l40 Tx #40

DC

DC

li Dispersion Monitor

Dispersion compensator (fixed or variable)

VIPA variable dispersion compensatorLine-focusing lens Optical circulator

DC > 0

Variable x-axis

DC < 0Glass plate

Collimating lens

Focusing lens3-Dimensional Mirror

VIPA : Virtually Imaged Phased Array11 Fujitsu

Dispersion compensation trendNE NE

Photonic network Manage dispersion or residual dispersion (dispersion map) !!NE NE NE

Transmitter / ReceiverAdjust parameters including residual dispersion to optimum!!12 Fujitsu

Polarization Mode Dispersion (PMD)Cross-section of optical fiberCladding Core

Ideal

PracticalFast axis

Slow axis

1st-order PMD

Fast

Dt DtSlowD t : Differential Group Delay (DGD)

- Well defined, frequency independent eigenstates - Deterministic, frequency independent Differential Group Delay (DGD) - DGD scales linearity with fiber length13 Fujitsu

Higher-order PMD D tn

D t1

D t2

D t3

D t4

Mode-coupling at random locations with random strengthMaxwellian distribution of the instantaneous DGD

-Statistically varying due to environmental fluctuations -Fiber PMD unit: ps/ km

Frequency of occurrence

-Frequency dependence of DGD

Prob.(DGD>3xPMD) = 4x10-5 = 21 min/year Prob.(DGD>3.5xPMD) =10-6 = 32 sec/year PMD 3.5PMD Instantaneous DGD (ps)

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Automatic PMD compensationPMD compensation scheme in receiverPMD comp. device #1 PMD comp. device #2 PMD comp. device #3 O/E module

40Gb/s waveforms Before PMD comp.

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 algorithm15 Fujitsu

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.

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