11

Improving Chromatic Dispersion Tolerance in Long-Haul Fibre Links

using Coherent OOFDM

  M. A. Jarajreh, Z. Ghassemlooy, and W. P. NgM. A. Jarajreh, Z. Ghassemlooy, and W. P. Ng

Optical Communications Research GroupOptical Communications Research Grouphttp://soe.unn.ac.uk/ocr/

School of Computing, Engineering and Information School of Computing, Engineering and Information SciencesSciences

University of Northumbria at Newcastle, University of Northumbria at Newcastle, UKUK

Contents OFDM and Optical OFDM (OOFDM) Applications of OOFDM Modems Coherent -OOFDM (CO-OOFDM)Modems Design CO-OOFDM Modems - Modelling (Matlab and VPi) Motivation Results

Back-to-Back Performance Back-to-Back Performance Effect of Number of Sub-carriers and CP on CD ToleranceEffect of Number of Sub-carriers and CP on CD Tolerance Effect of Number of Sub-carriers ON Transmission performanceEffect of Number of Sub-carriers ON Transmission performance Effect of Sampling Speed on CD ToleranceEffect of Sampling Speed on CD Tolerance Effect of Sampling Speed on Transmission Performance in Fibre LinksEffect of Sampling Speed on Transmission Performance in Fibre Links The Effect of Adaptively Modulated CO-OOFDM on CD ToleranceThe Effect of Adaptively Modulated CO-OOFDM on CD Tolerance

Conclusions

OFDM

33

Orthogonal Frequency Division Multiplexing (OFDM)

Harmonically related narrowband sub-carriers The sub-carriers spaced by 1/Ts The peak of each sub-carrier coincides with trough of

other sub-carriers

Splitting a high-speed data stream into a number of low-speed streams

Different sub-carrier transmitted simultaneously

44

What is OOFDM By introducing OFDM in the optical domain, Optical OFDM

(OOFDM) was generated

Advantages of OOFDM Cost-effective High-speed Excellent flexibility and robustness

Optical OFDM

55

Access and local area networks IMDD modems

Future high-capacity long-haul networks Coherent modems

Combating optical fibers dispersion and polarization mode dispersion

Applications of OOFDM Modems

Coherent -OOFDM Modems Design

66

CO-OOFDM modem diagram used in numerical simulations, (dotted line is either fibre or integrated optics)

CO-OOFDM Modems - Modelling Matlab: easy to model the OFDM modem

32-QAM modulation

32-QAM detection with additive noise

77

-5 -4 -3 -2 -1 0 1 2 3 4 5-5

-4

-3

-2

-1

0

1

2

3

4

5

REAL

IMA

G

-8 -6 -4 -2 0 2 4 6 8-8

-6

-4

-2

0

2

4

6

8

REAL

IMA

G

CO-OOFDM Modems – Modelling

88

Screen shots (Coherent OFDM System)

(Virtual Photonic Inc.) VPi Software

99

• The achievable signal transmission capacity of an Optical Orthogonal Frequency Division Multiplexing (OOFDM) modem over Single Mode Fibre (SMF) links is affected considerably by:• Fibre Chromatics Dispersion (CD)

• Number of sub-carriers• Cyclic prefix

• Fibre nonlinearity• Optical launch power

• Numerical simulations are undertaken to investigate the above-mentioned effects on the system performance of Coherent OOFDM

Motivation

1010

Results

Work will be presented

Back-to-back Performance

Effect of number of subcarriers and Cyclic Prefix (CP) on Chromatic Dispersion (CD) Tolerance

Effect of sampling speed on CD tolerance

The result of utilizing AM-CO-OOFDM on CD tolerance

1111

Simulation ParametersParameters Values

No. of subcarriers 64Wavelength 1550 nmLight source Laser diode

Photodetector PINPhotodetector responsivity

0.9

Fibre span 80 kmChromatic dispersion 17 ps/nm/km

Fibre loss 0.2 dB/kmADC/DAC

- sampling rate- clipping ratio- quantization

12.5 GS/s13 dB10 bits

Data rates- DBPSK- DQPSK- 16-QAM- 32-QAM- 64-QAM

- 128-QAM- 256-QAM

10 Gb/s20 Gb/s 40 Gb/s50 Gb/s60 Gb/s70 Gb/s80 Gb/s

Low pass filter order and 3-dB bandwidth

2nd & 6.5GHz

EDFA spanEDFA gain

EDFA noise figure

80km16 dB6 dB

1212

Back-to-Back Performance

Quantization and clipping effects were switched off

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 5 10 15 20 25 30OSNR (dB)

BER

256 QAM

64QAM

32QAM16QAMDQPSK

128QAMDBPSK

1313

Adjacent Symbol Interference (ASI) Symbol Smearing Due to Channel

1414

Cyclic Prefix Inserted in Guard Interval to Suppress Adjacent

Channel Interference

1515

Effect of Number of Sub-carriers and CP on CD Tolerance

Cyclic prefix is more effective if compared with the number of subcarriers in combating dispersion

1616

Effect of Number of Sub-carriers ON Transmission performance

With -6dBm launch power, 64 subcarriers is the optimum number of subcarriers

1717

Effect of Sampling Speed on CD Tolerance

Lower sampling speed can increase CD tolerance for a fixed number of subcarriers

1818

Effect of Sampling Speed on Transmission Performance in Fibre

Links

With the presence of non-linearity, lower sampling speed does not mean higher performance

1919

The Effect of Adaptively Modulated CO-OOFDM on CD Tolerance

Adaptively modulating the CO-OOFDM subcarriers increases CD tolerance

2020

Conclusions For coherent OOFDM modems, for a given modulation

format, increasing the number of sub-carriers or cyclic prefix length, increases dispersion tolerance effectively

A longer length CP is more effective in combating fibre dispersion than use of large number of sub-carriers

For coherent OOFDM Modem the optimum launched power is -6 dBm

For a given number of subcarriers sampling speed can increase the system dispersion tolerance

Utilizing CO-AMOOFDM increases the system tolerance to CD

2121

Thank you for your attention !

Any questions?

2222

Email: Email: Mutsam.jarajreh@Northumbria.ac.uk

Web: Web: http://soe.unn.ac.uk/ocr/

Tel: 00 44 191 227 4902Tel: 00 44 191 227 4902

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