Investigations on PMD-induced penalties in 40 Gbps optical transmission link

Irfan Ullah Department of Information and Communication Engineering Myongji university, Yongin, South Korea

Published in Optik 121(2010)286–290 Copyright © solarlits.com

Contents

1. Introduction2. System description3. Simulation and results4. Conclusions and Future Work

• To increase data rate in a specific time• WDM and TDM can be used

• To increase capacity demand (more than 40 Gbps)• Chanel data rate• WDM channels

• Polarization mode dispersion (PMD)• occurs in long-haul transmission

Introduction

2.5 Gbps•Bit period is long•No pulse distortion

40 Gbps or above•Bit period is short•Pulse distortion•PMD is important

Birefringence is the cause of occurrence of PMD.“Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light”

• Refractive index variation causes• Differential group delay (DGD), which increases inter symbol interference (ISI)

and bit error rate (BER)• At 40 Gbits the DGD of a transmission line may easily exceed one

bit duration T• Automatic compensation of 30 ps of DGD in a 40 Gbits optical

transmission system using three PMD penalty extraction signals with BPFs centered at 0.5/T, 0.25/T, 0.125/T and cut off frequency has been analyzed.

Introduction

• Laser 40 Gbps at 1550 nm• RZ modulated signal• Fiber: 100 Km• PMD coefficient DP = 3.16 x 10-14 x PMDcoef.• Fiber with two different PMD values: 0.1 and 1.0ps/km1/2

System description

• PMD effect (Coarse-step PMD method ) was turned ON

• PMD causes DGD between x and y polarization• Eye distortion at the receiver.

• DGD can be calculated by

• 1 and 10 ps for a PMD coefficient of 0.1 and 1.0 ps/km1/2,

System description

Low PMD fiber

High PMD fiber

• PMD and non-linearities including Raman effects.

• All Raman effects in the present model were disabled

System description

• Combined optical signal output of X and Y polarization axes

• Low PMD: maintain integrity and magnitude• High PMD: Pulses merged causing ISI and reduction in

the magnitude/signal level

Results

Low PMD fiber

High PMD fiber

• Q2 (dB) of the low-PMD: 16.0 dB• Q2 (dB) of the high-PMD: 14.25 dB

• BER of the low-PMD: 10-10

• BER of the high-PMD: 10-7

Results

Low PMD fiber

High PMD fiberLow PMD fiber High PMD fiber

• Q2 (dB) of the low-PMD: 16.0 dB• Q2 (dB) of the high-PMD: 14.25 dB

• BER of the low-PMD: 10-10

• BER of the high-PMD: 10-7

Results

BER, Q2 (dB) values for low and high PMD fibers

DGD for low and high PMD fibers

• Points are distributed evenly on a sphere• Three-dimensional evaluation yields

• DGD• Degree of polarization (DOP)• Second-order PMD.

• Low DGD results in even distribution of points around the sphere

• The increase in DGD results in elliptical distribution of points

Results

Poincare sphere plot for Stokes parameters

• Shows the distribution/variation of Stokes parameters• With respect to random seed ranging from 0 to 50 for both low and

high PMD fibers

Results

Stokes parameters S1 Stokes parameters S2 Stokes parameters S3

• Q2 (dB) remains absolutely constant in case of low-PMD fibers

• Varies randomly between 9 and 16 dB for high-PMD fibers

Results

Q-factor vs. DGD

Conclusions

• Obtained the results for DGD, BER, Q2 (dB) for different values of the PMD coefficient and different random seeds• PMD coefficient takes the two values for low- and high-PMD fibers• PMD seed parameter takes values ranging from 1 to 50

• PMD-induced DGD degrades system performance with penalties

Thanks ?