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Dispersion Compensation Techniques for Optical Fiber Communication

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Dispersion Compensation Techniques for Optical Fiber Communication

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Dispersion Compensation Techniques for Optical Fiber Communication

  1. 1. Presented By:- AMIT 3PD14LCS01
  2. 2. CONTENTS  INTRODUCTION  DISPERSION CATEGORIES  DISPERSIONTECHNIQUES  APPLICATIONS  ADVANTAGES  DRAWBACKS  CONCLUSION
  3. 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. 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. 5. Modal dispersion Chromatic dispersion Polarization dispersion
  6. 6. Dispersion Techniques  Dispersion Compensating Fibers  Fiber Bragg Grating  Electronic dispersion compensation  Digital Filters  Optical Phase Conjugation Techniques
  7. 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. 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. 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. 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
  11. 11. 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.
  12. 12.  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.
  13. 13. 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.
  14. 14. 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.
  15. 15. 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.
  16. 16. 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.
  17. 17. 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.
  18. 18. 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.

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