光纤通信课程设计课件Class7-03.pptx

Class 7Class 7Raman Fiber AmplificationEDFAStructureParametersSelectionGain flatteningExerciseReasons to use the optical amplifiers:Broadband:possible for the S-band and even 2nd windowExcellent for ultra long-haulHigh channel count(more than 80)High modulation speed(40Gbit/s)Low noiseLonger distances between regenerationRaman Fiber Amplifier Amplification Mechanism SRS Stimulated Raman ScatteringElastic scatteringInelastic scatteringAlowerfrequencysignalphotonInduces!theinelasticscatteringofahigher-frequency pump photon in an optical medium in the nonlinear regime.Raman Effect:Inelastic scattering of a photonDiscovered by C.V.Raman in 1928,Nobel Prize in 1930 When light is scattered from an atom or molecule,most photons are elastically scattered(Rayleigh scattering),a small fraction of the scattered light(approximately 1 in 10 million photons)is scattered by an excitation,with the scattered photons having a frequency different from,and usually lower than,the frequency of the incident photons.In a gas,Raman scattering can occur with a change in vibrational or rotational energy of a molecule.Occurs in liquids,gases,and solidsRaman Effect:Inelastic scattering of a photonRaman Effect in Silicate GlassOne signal photon in,two out!One signal photon in,two out!Raman Fiber Amp:Characteristics No need of doped fiber，transmission fiber-gain medium Nonlinear effect Detune 100nm,amplify any band by choosing appropriate pump wavelengths Multi-pump configuration-flat-gain broadband amplification Simple structureDisadvantagesStrong pumping powerRaman effect:conversion from higher-lower frequency-cross-talk-noiseRaman Effect:Inelastic scattering of a photonDiscovered by Sir Chandrasekhara Venkata Raman,Nobel Prize in 1930 When light is scattered from an atom or molecule,most photons are elastically scattered(Rayleigh scattering),a small fraction of the scattered light(approximately 1 in 10 million photons)is scattered by an excitation,with the scattered photons having a frequency different from,and usually lower than,the frequency of the incident photons.4 In a gas,Raman scattering can occur with a change in vibrational or rotational energy of a molecule(see energy level).Chemists are concerned primarily with the vibrational Raman effect.Occurs in liquids,gases,and solidsRaman Fiber Amp:History SRS in fiber observed in 1972 1973 Stolen and Ippen measured Stokes shift in fused silica 13.2THz 1976 Anyeung and Yariv established theory 1995 Emori utilized 14xx nm pumping to obtain 100nm broadband amplification with a flatness of forward-noise Short upper-state lifetime(3-6fs)Virtually instantaneous gain:pump fluctuation couples to signal-RIN ASE Phonon-stimulated optical noiseThermally induced phonons in fiber that can spontaneously experience gain from the pumps,thereby creating noise for signals close to pump wavelengthsNoise Figure in EDFAEnergy Transfer in Raman AmplificationNoise FigureNoise figure v.s.alpha,fiber loss at pump wavelengthNoise FigureNoise figure v.s.gain for various values of fiber lengthsIn-class Exercise Design a multi-pump Raman amplifier Optimize/flatten gain by adjusting pumping powers Homework:EDFA+Raman hybrid ampOne PumpThree PumpsTwo Pumps