Dispersion Compensation Techniques for Optical Fiber Communication

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.