EE 230: Optical Fiber Communication Lecture 4
From the movieWarriors of the Net
Fiber 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
Group velocity
Group delay
Dispersion
1
gv
kc
1
D
Wave Packet Construction
Group and Phase Velocity
Transform Limited Frequency Spread
Optics-Hecht & Zajac
Rectangular Pulse Pulse modulated Sine wave
Gaussian modulated Sine wave
Spectral properties of digitally modulated signals1
.
BitTime T
Time
RZEncodedData
NRZEncodedData
1 0 1 1 0 0 1
Frequency1/T 2/T 3/T
P o w e r
No spectral component at the clock frequencyFor Non-Return to Zero Encoded Data
Pulse Propagation through Fibers
Fundamentals of Photonics - Saleh and Teich
Response of a multi-mode fiber to a single short pulse
Broadening of a short pulse after transmission through different types of fibers
Material Dispersion
Refractive Index of Pure Silica and its derivatives
Fiber Optic Communications-Palais
Material Dispersion Parameter for pure silicaand germanium doped silica
Optical Fiber Communications-Keiser
Zero Dispersion Slope
Fiber Optics Communication Technology-Mynbaev & Scheiner
Fiber Dispersion
Pulse Degradation from Dispersion
Ray optics View of the origin of waveguide dispersion
Typical fiber Dispersion Curve
Dispersion:The change in speed of propagation with wavelength
Polarization Mode Dispersion
Polarization Maintaining Fiber
Non-Polarization Maintaining Fiber
Random power transfer occurs between different polarization modesas the pulse propagates, if the two modes have different propagation velocitiesthen the pulse will broaden
Representative Fiber Characteristics
Dispersion for various Fiber Types
Dispersion Shifted and Dispersion Flattened Fibers
Fundamentals of Photonics - Saleh and Teich
Waveguide Dispersion mechanism
AsMode field diameter More of the mode travels in the cladding.Cladding index is lower so pulse velocity resulting in dispersion
Chromatic Dispersion Parameters ofa singlemode fiber
Comparison of Dispersion Characteristics
Propagation of Gaussian Pulses
Input Pulse Output Pulse chirped and broadened
Input PulseAlready PositivelyChirped
After some distancethe chirp is removedand the pulse assumes its minimum possible width
Upon further propagation the pulse will continue to broaden and acquire chirp.
2<0 for standard single mode silica fiber
and Ld ~ 1800 km at 2.5 Gb/s and ~115 km at 10 Gb/s
Optical Networks a Practical Perspective-Ramaswami and Sivarajan
Top Related