This document discusses dispersion in optical fiber communication systems and various techniques to compensate for it, including dispersion compensating fibers, fiber Bragg gratings, electronic dispersion compensation, digital filters, and optical phase conjugation. Dispersion increases pulse spreading and affects signal quality. These techniques help reduce dispersion to improve transmission over long distances. The document compares the advantages and disadvantages of each technique.

1. Presented By:-
AMIT
3PD14LCS01

2. CONTENTS
 INTRODUCTION
 DISPERSION CATEGORIES
 DISPERSIONTECHNIQUES
 APPLICATIONS
 ADVANTAGES
 DRAWBACKS
 CONCLUSION

3. INTRODUCTION
Optical fiber communication is a method of transmitting
information from one place to another by sending pulses of
light trough optical fiber.
Optical communication system faces problems like
dispersion, attenuation and non-linear effects.
Among them dispersion affects the system the most.
Dispersion is defined as pulse spreading in an optical fiber.
Dispersion increases along the fiber length.

4. Dispersion Categories
 Modal dispersion- Pulse spreading caused by time delay.
 Chromatic dispersion-Pulse spreading caused by different
wavelength of light propagate by different velocities.
• Material dispersion-Wavelength dependency on
index of refracting of glass.
• Waveguide dispersion-Due to physical structure of
the waveguide.
 Polarization mode dispersion- Dispersion occurs due to
Birefringence.

5. Modal dispersion
Chromatic dispersion Polarization dispersion

6. Dispersion Techniques
 Dispersion Compensating Fibers
 Fiber Bragg Grating
 Electronic dispersion compensation
 Digital Filters
 Optical Phase Conjugation Techniques

7.  DCF modules inserted
into transmission line at
regular interval.
 Relative dispersion slope
RDS=S/D
 Dispersion is 100ps/nm
for 40 Gbit/s signal.
Dispersion Compensating Fibers
(DCF)

8.  DCF has negative dispersion.
 Low loss module is used to
relax the gain, but improve the
noise figure.
 Attenuation is 0.40 dB/km.
Chromatic dispersion is
-152 ps/nm/km.
 Chromatic dispersion is 1.3
times the normal.

9.  Attenuation is increased over the
wavelength of 1570nm bending loss
is not observed.
 Maximum insertion loss at
-40℃.
 Variation in temperature lead
insertion loss is less than 0.5dB.
 Attenuation is 0.53 dB/km.
 Chromatic dispersion is
-160ps/nm/km.
Attenuation is increased at
wavelength longer than 1575nm.
 Maximum insertion loss for
wavelength 1550nm at -40℃.
 Variation in temperature lead
insertion loss is less than 0.1dB.

10. Fiber Bragg Grating
(FBG)
 It is periodic perturbation of refractive index along the fiber length.
 Back reflected light from the fiber produces effect called
“Photosensitivity”.
 Bragg’s law
ᴧ=λ/2

12. Electronic dispersion compensation
(EDC)
 It is used for CHROMATIC dispersion compensation.
 Block A contains the optical components generating two signals.
 Block B produces two electric signals VA and VF.
 Block C Local oscillator is modulated for VA and VF.
 Block D contains Dispersion transmission line.

13.  EAM designed for short reach
applications for 10Gb/s.
 Amplifier has a noise figure of
4.5dB.
 20dB loss over a transmission
length of 100km.
 Eye diagram for transmission
over 600km.

14. Optical Phase Conjugation
Techniques
 Compensation of CHROMATIC dispersion in single mode fiber.
 Block consist of Transmitter, Fiber, Phase conjugator.
 Data stream is 10Gb/s ,Dispersion is 16ps/nm/km.
 Eye diagram after 1000km of the transmission.

16. Digital Filters
 Filter used for compensation is All Pass Filter.
 APF is used to equalize a phase of signal without introducing any
amplitude distortion.
 Dispersion is compensated with very low loss.
 Performance can be increased by increasing number of stages.
 Figure shows the eye diagram at the receiver at 160km.

18. ADVANTAGES
 Low insertion loss and higher performance in Dispersion
compensating fiber.
 Improvement in average Bit error rate and error vector magnitude in
Electronic dispersion compensation.
 Small footprint, low insertion loss, dispersion slope compensation in
Fiber grating.
Phase conjugation technique is more reliable to high frequency signals.
 All pass filters can be designed to compensate optical fiber dispersion
for large bandwidth with low loss and ripple.

19. DISADVANTAGES
 Dispersion compensating fibers gives large foot print and insertion
losses at very low temperature.
 Electronic dispersion compensation slows down the speed of
communication since it slows down the digital to analog conversion.
 Architectures using Fiber Bragg grating is complex.
 In all pass filter at lower amplitude of the pulse, the filter results in a
larger spread.
 The increased pulse width at lower amplitude will affect the bit error
rate and introduce ISI.
 Phase conjugation is more complex and costly.

20. APPLICATIONS
 Compensation of dispersion-broadening in long-haul communication
in FBG.
 Microwave and millimeter wave frequency application in APF.
 Application in LAN, MAN, 10G-Ethernet in EDC.
Applications are in the fields of light wave communications and optical
fiber sensors which are based on the existence of photosensitivity in
silica optical fibers and optical waveguide in DCF.
 Application areas: such as high-brightness laser oscillator/amplifier
systems, cavity-less lasing devices, laser target-aiming systems,
aberration correction for coherent-light transmission and reflection
through disturbing media, long distance optical fiber communications
with ultra-high bit-rate, optical phase locking and coupling systems, and
novel optical data storage and processing systems in Optical Phase
Conjugation.

21. CONCLUSION
 Fiber-optic communication because of its advantages over electrical
transmission, have largely replaced copper wire communications in core
networks in the developed world. But it is also marred by many
drawbacks: dispersion, attenuation and non linear effect.
From this study it is clear that different researchers have used different
techniques for dispersion compensation in optical system.
We consider five techniques in our consideration, but Phase
conjugation technique is the best technique to reduce the dispersion.