Presented By:-AMIT3PD14LCS01

Dispersion Compensation Techniques for Optical Fiber

Communication

CONTENTS

INTRODUCTION DISPERSION CATEGORIES DISPERSION TECHNIQUES APPLICATIONS ADVANTAGES DRAWBACKS CONCLUSION

INTRODUCTIONOptical 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.

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.

Modal dispersion

Chromatic dispersion Polarization dispersion

Dispersion Techniques

Dispersion Compensating Fibers

Fiber Bragg Grating

Electronic dispersion compensation

Digital Filters

Optical Phase Conjugation Techniques

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)

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.