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. Fiber Optics Communication Technology-Mynbaev & Scheiner
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
Input Pulse
Already Positively
Chirped
After some distance
the chirp is removed
and the pulse assumes its
minimum possible width
Upon further propagation
the pulse will continue to broaden
and acquire chirp.
Optical Networks a Practical Perspective-Ramaswami and Sivarajan