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EE 230: Optical Fiber Communication Lecture 4

EE 230: Optical Fiber Communication Lecture 4. Fiber Dispersion. From the movie Warriors of the Net. Types of Dispersion. Modal dispersion: different modes propagate at different group velocities Material dispersion: the index of refraction of the medium changes with wavelength

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EE 230: Optical Fiber Communication Lecture 4

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  1. EE 230: Optical Fiber Communication Lecture 4 Fiber Dispersion From the movie Warriors of the Net

  2. Types of Dispersion • Modal dispersion: different modes propagate at different group velocities • Material dispersion: the index of refraction of the medium changes with wavelength • Waveguide dispersion: index change across waveguide means that different wavelengths have different delays • Polarization mode dispersion: if waveguide is birefringent

  3. Definitions Group velocity Group delay Dispersion

  4. Wave Packet Construction

  5. Group and Phase Velocity

  6. Transform Limited Frequency Spread Pulse modulated Sine wave Rectangular Pulse Optics-Hecht & Zajac Gaussian modulated Sine wave

  7. Spectral properties of digitally modulated signals1 No spectral component at the clock frequency For Non-Return to Zero Encoded Data

  8. Pulse Propagation through Fibers Response of a multi-mode fiber to a single short pulse Broadening of a short pulse after transmission through different types of fibers Fundamentals of Photonics - Saleh and Teich

  9. Material Dispersion Refractive Index of Pure Silica and its derivatives Material Dispersion Parameter for pure silica and germanium doped silica Optical Fiber Communications-Keiser Fiber Optic Communications-Palais

  10. Zero Dispersion Slope Fiber Optics Communication Technology-Mynbaev & Scheiner

  11. Fiber Dispersion Dispersion:The change in speed of propagation with wavelength Pulse Degradation from Dispersion Typical fiber Dispersion Curve Ray optics View of the origin of waveguide dispersion

  12. Polarization Mode Dispersion Polarization Maintaining Fiber Non-Polarization Maintaining Fiber Random power transfer occurs between different polarization modes as the pulse propagates, if the two modes have different propagation velocities then the pulse will broaden

  13. Representative Fiber Characteristics

  14. Dispersion for various Fiber Types

  15. Dispersion Shifted and Dispersion Flattened Fibers Chromatic Dispersion Parameters of a singlemode fiber • Waveguide Dispersion mechanism • As l Ý,Mode field diameter Ý • More of the mode travels in the cladding. • Cladding index is lower so pulse velocity Ý • resulting in dispersion ß Fundamentals of Photonics - Saleh and Teich

  16. Comparison of Dispersion Characteristics

  17. Propagation of Gaussian Pulses Input Pulse Output Pulse chirped and broadened b2<0 for standard single mode silica fiber and Ld ~ 1800 km at 2.5 Gb/s and ~115 km at 10 Gb/s Upon further propagation the pulse will continue to broaden and acquire chirp. Input Pulse Already Positively Chirped After some distance the chirp is removed and the pulse assumes its minimum possible width Optical Networks a Practical Perspective-Ramaswami and Sivarajan

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