Slide 1

WDM System & Crosstalk

Presented by :-

Rajarse Sen (Roll no.-09)

Souvik Koner (Roll no.- 20 )

Sudip Kumar Nandi (Roll no.-31)

Pratip Rana (Roll no.-65)

Debjyoti Das (Roll no.-66)

Outline :

WDM System definition & overview

Advantages of WDM System

Types of WDM System

Linearity & Non-linearity in WDM System

Types of Non-linear Crosstalk

Stimulated Scattering-SRS & SBS

Optical Kerr Effect-SPM,XPM & FWM

Reduction of FWM

What is WDM system?

Multiplexing optical signals onto a single fiber using different wavelengths

Attractive multiplexing technique

High aggregate bit rate

Low dispersion

Very useful for upgrades to installed fibres

Realizable using commercial components, unlike OTDM

Loss, crosstalk and non-linear effects are potential problems

Wavelength Division Multiplexer

Wavelength Division Demultiplexer

l1

A

l2

l3

B

C

l1

X

l2

l3

Y

Z

l1 + l2 + l3

Fibre

WDM Overview :

4

Advantages of Optical Communication:

Enormous Bandwidth

Immunity to crosstalk

Electrical Isolation

Small size & weight

Security

Ruggedness & flexibility

Low cost & availability

Reliability

Two types of WDM system :

Linearity & Non-linearity in WDM system:

Linear vs. Non-linear effects:

Linear response due to weak field

Non-linear response at strong field

Types of Non-linear crosstalk:

Stimulated Scattering : Interaction between the optical signals and the molecular or acoustic vibrations in a fiber

Optical Kerr Effect : High power causes change in Refractive

index which in turn produces this effect

Stimulated Raman Scattering(SRS):

Energy

Excited State

Ground State

s

Virtual Energy State

Pump wave

p

Optical Phonon

Steokes wave

p

Caused by interaction of light with molecular vibrations.

Portion of light (pump wave) traveling at each frequency is downshifted across region of lower frequencies => Stokes wave.

Fraction of power transferred to Stokes wave grows rapidly with increasing power of input signal.

SRS occur when the light launched into the fibre exceeds a threshold power level for each process.

Stimulated Raman Scattering (Continued) :

2

3

5

4

1

Optical Fiber

Input Spectrum

2

3

5

4

1

1