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Power Considerations in Optical Transmission Systems in Presence of Nonlinear Phase Noise

This paper discusses Kerr nonlinearity, optimal power profile design, and power considerations in WDM systems, exploring nonlinear phase noise and its impact on coherent communication systems. It examines factors affecting power levels design and variance minimization strategies.

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Power Considerations in Optical Transmission Systems in Presence of Nonlinear Phase Noise

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  1. Power Considerations in Optical Transmission Systems in Presence of Nonlinear Phase Noise Alan Pak Tao Lau Department of Electrical Engineering, Stanford University May 26, 2006

  2. Outline • Kerr nonlinearity induced nonlinear phase noise in coherent communication systems • Optimal and practical power profile design for variance minimization • Power profile design in WDM systems

  3. Kerr Nonlinearity • Centro-symmetric materials • induced intensity dependent refractive index

  4. Nonlinear effects in coherent communications systems • Kerr induced nonlinear phase shift where • Self Phase Modulation (SPM) • Cross Phase Modulation (XPM) • Typical ranges of : 1~5 /(W km)

  5. Nonlinear phase noise Fiber Opt. Amp. • ASE from inline amplifiers generate Gaussian noise • Random power of signal plus noise produce random nonlinear phase shift -- Gordon-Mollenauer effect overall length L with N spans L=3000 km, N=30, = 0dBm

  6. Fiber Fiber Fiber Optical Amp. Optical Amp. Optical Amp. Phase Noise for coherent systems • Linear Phase Noise • Nonlinear Phase Noise

  7. System design for variance minimization • Total variance of phase noise • Last time, looked at how we can design the gain and spacings of inline amplifiers to minimize variance of phase noise • We’ll look at how signal power at different points in the system affects

  8. Factors affecting Power Levels Design • High power – Nonlinear phase noise, amplifier gain saturation • Low power – Linear phase noise, input coupling loss, shot noise and thermal noise, quantum effects • Allowable Range of Power levels

  9. Optimal Operating Power Transmitted Power = Received Power = P

  10. Optimal Operating Power • Mean nonlinear phase shift • Corresponds with literature findings

  11. Unequal Input and Received Power • Amplifiers over or under compensate the signal loss along the link • Study a linearly increasing/decreasing power profile along the link.

  12. Unequal Input and Received Power

  13. Linear Power Profile • Good to have a drop in received power

  14. Optimal Power Profile • Power profile • Let • Phase noise variance • Euler Characteristic Equation

  15. Optimal Power Profile

  16. Power profile design in WDM systems • Cross-phase modulation (XPM) • Difference in group velocity -- Walk Off Effect • Pulse waveform distortion negligible compared to walk off in modeling

  17. XPM induced nonlinear phase noise • Assumptions: Flat gain amplifiers and noise spectrum • Typical spacing: 10Gb/s, 50 GHz, D=4 ps/(km-nm) --> Lw=62.5 km

  18. Power Profile Design in WDM systems

  19. Power Profile Design in WDM systems • Objective

  20. Power Profile Design in WDM systems • Power drop profile requires less pump energy Future Work • Real systems aren’t point to point • Signal path routed by RODAM • Power drop profile should still provide benefits

  21. Acknowledgements • Prof. Kahn • Dany, Ezra and Rahul =) Thank you !

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