ece228 lecture 7

ece228 lecture 7 - Bowers ECE 228A Polarization and Raman...

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Bowers ECE 228A Polarization and Raman Lecture #7 John Bowers ECE 228A Read Chapter 2. Also, Agrawal: Nonlinear Fiber Optics (on reserve)
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Bowers ECE 228A Dispersion Management •W e v e d i s c u s s e d Material dispersion – Waveguide dispersion –M o d a l d i s p e r s i o n •M o d a l d i s persion is solved by using single mode fiber. •T h e f i b e r d i s p e r s i o n ( m a t e r i a l p l u s w a v e g u i d e ) i s s o l v e d b y d i s p e r s i o n management: Use low dispersion fiber and compensate at the end for zero total dispersion. Net dispersion Distance ECE 228A This can be repeated many times over a long distance. The final compensation amount differs for each wavelength.
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Bowers ECE 228A Origin of Dispersion and Nonlinearities The refractive index of the fiber depends upon both the frequency and the power of the signal n ( Z , P ) Chromatic Nonlinearities Dispersion (1)Self-phase Modulation (SPM) (2)Cross-phase Modulation (XPM) (3 Fou wave Mixing (FWM (3)Four-wave Mixing (FWM) (4)Stimulated scattering
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interact. Bowers ECE 228A Effect of Dispersion * FWM and CPM require phase matching of two co-propagating channels. Dispersion destroys phase matching!!! D = 0 channels propagate together. D ő 0 channels walk-off and don±t
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Bowers ECE 228A Four Wave Mixing and Dispersion Z Z ± Z ² Z Z ± Z ² ²Z ² ³Z ± ²Z ± ³Z ² DSF D ~ 0 Into Fiber Out of Fiber DSF D 0 Degradation on Bit Stream (Equal Channel Spacing) Degradation on Optical Spectrum (Unequal Channel Spacing) D = -0.2 (ps/nm/km) -10 -20 Bm) D = -1 (ps/nm/km) D = -2 -30 -40 Power (d 16 ns 21 ns 26 ns (ps/nm/km) 1542 1544 1546 1548 Wavelength (nm) D. Marcuse, JLT, 1994 USC Optical Laboratory Communications K.M.F. ofcshortcourse.kmf.dispersion.3
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Bowers ECE 228A Dispersion Management Concept D z 0 D z 0 D total = 0 Chromatic dispersion time time SMF D = 0 XPM and time time time DCF SMF Effects are minimized FWM time time DSF minimized USC Optical Labo a o y Communications
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Bowers ECE 228A Methods for Dispersion Compensation Linearly-Chirped Fiber Bragg Grating Dispersion Compensating Fibe Inciden Compensating Fiber D 17 ps/(nm.km) O 1 O 3 O ± O ² O ³ Incident O O ´ -80 ps/(nm.km) Reflected No obvious method to tune dispersion USC Optical Communications
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Bowers ECE 228A Fiber Bragg Grating: Concept and Configuration T UV Light Photosensitive fiber Interference Pattern Chirped FBG Uniform FBG n O Reflection O ransmissio O ± O ² O 1 O 1 O ± O ² Incident T O O Chirped Pitch Reflected Uniform Pitch USC Optical Laboratory Communications
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Bowers ECE 228A A Typical Chirped Fiber Bragg Grating B) tivity (d y (ps) d Reflec me Dela Slope (ps/nm) = malized Ti Slope (ps/nm) = dispersion Wavelength (nm) Nor USC Optical Laboratory Communications K.M.F.
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ece228 lecture 7 - Bowers ECE 228A Polarization and Raman...

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