210 likes | 215 Views
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. Outline . Kerr nonlinearity induced nonlinear phase noise in coherent communication systems
E N D
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
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
Kerr Nonlinearity • Centro-symmetric materials • induced intensity dependent refractive index
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)
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
Fiber Fiber Fiber Optical Amp. Optical Amp. Optical Amp. Phase Noise for coherent systems • Linear Phase Noise • Nonlinear Phase Noise
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
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
Optimal Operating Power Transmitted Power = Received Power = P
Optimal Operating Power • Mean nonlinear phase shift • Corresponds with literature findings
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.
Linear Power Profile • Good to have a drop in received power
Optimal Power Profile • Power profile • Let • Phase noise variance • Euler Characteristic Equation
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
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
Power Profile Design in WDM systems • Objective
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
Acknowledgements • Prof. Kahn • Dany, Ezra and Rahul =) Thank you !