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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
EE 230: Optical Fiber Communication Lecture 4

Fiber Dispersion

From the movie

Warriors of the Net

types of dispersion
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
definitions
Definitions

Group velocity

Group delay

Dispersion

transform limited frequency spread
Transform Limited Frequency Spread

Pulse modulated Sine wave

Rectangular Pulse

Optics-Hecht & Zajac

Gaussian modulated Sine wave

spectral properties of digitally modulated signals1
Spectral properties of digitally modulated signals1

No spectral component at the clock frequency

For Non-Return to Zero Encoded Data

pulse propagation through fibers
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

material dispersion
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

zero dispersion slope
Zero Dispersion Slope

Fiber Optics Communication Technology-Mynbaev & Scheiner

fiber dispersion
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

polarization mode dispersion
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

dispersion shifted and dispersion flattened fibers
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

propagation of gaussian pulses
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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