ece 228 lecture 9

ece 228 lecture 9 - Lecture 9 - Fiber Nonlinearties ECE...

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Lecture 9 - Fiber Nonlinearties ECE 228A 9.1
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Fiber Nonlinearities In principle, we can continue to increase the optical power at the transmitter to overcome power penalties and limitations to SNR due to amplifier and receiver noise sources But ! We if we try to increase the optical power per channel too much, the signal will start to degrade due to distortion and crosstalk caused by nonlinearities in the fiber and amplifiers his means that the effective receiver sensitivity will be decreased or This means that the effective receiver sensitivity will be decreased or limited We have to limit the input power injected into the fiber in order to avoid nonlinearities The limits depend on the dominant nonlinear mechanism, the link and channel configurations and other link/network parameters ECE 228A 9.2
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Fiber Non-linearity Impairments There are several conditions where the optical power in the fiber can actually cause signal distortion or crosstalk with other optical wavelengths Self-Phase Modulation (SPM) Kerr Effects Cross-Phase Modulation (CPM) Four-Wave Mixing (FWM) ti ulated Ra an Scattering (SRS) Scattering Effects Stimulated Raman Scattering (SRS) Stimulated Brillouin Scattering (SBS) general these effects limit the In general, these effects limit the Amount of power per wavelength that can be carried in the fiber The number of wavelengths per fiber The channel spacing between wavelengths per fiber ECE 228A 9.3 pg g p Bit rate per wavelength vs. number of wavelengths that can be supported
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Nonlinear Effects Raman scattering Optical phonon process Optical honons Input 1 Output 1 - B B 2 10-20 THz coustic L Phonons Brillouin scattering Acoustic Phonons Transverse Acoustic phonon process Input 1 Output 1 - B Output opposite direction from input ECE 228A 9.4
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Raman Effects Raman effects are important As a detrimental effects: it takes place in recent systems with a very high number of WDM channels (>64 ch.) It induces a tilt in the WDM comb, together with the aforementioned crosstalk effect As a positive effect, for distributed Raman amplification strong pump at a lower wavelength is launched in a counter ropagating A strong pump at a lower wavelength is launched in a counter-propagating direction inside the fiber A distributed amplification is obtained, as seen in a previous section Raman distributed amplification is an hot issue in optical transmission The most recent “records” in transmission capacity have been obtained using Raman amplification ECE 228A 9.5
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Raman Scattering Stokes Scattering-Downshifted light Input light Output light Antistokes Scattering-Upshifted light Intensity is orders of magnitude smaller than Stokes scattering Acoustic energy Output light ECE 228A 9.6 Acoustic energy
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Effective Fiber Length ny onlinear effect depend rongly on the optical intensity within the fiber Any nonlinear effect depends strongly on the optical intensity within the fiber.
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This document was uploaded on 01/29/2011.

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ece 228 lecture 9 - Lecture 9 - Fiber Nonlinearties ECE...

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