Lect 3.7 - Department of Electrical and Computer...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Department of Electrical and Computer Engineering ECSE 352 Electromagnetic Waves and Optics 3.7 Dispersive materials and group velocity References: Hayt and Buck 3.7 and 3.8 @Andrew Kirk 3.7-1 Overview In most real materials, and also in waveguides, the phase velocity is not constant but instead varies with frequency. This has very important consequences for the propagation of signals that are carried by electromagnetic waves in these materials and systems. Wewill see that thisresults in signaldispersion , which is a type of distortion. In order to describe this effect we will introduce the concept of group velocity . ECSE 352 3.7-2 Learning outcomes After taking this class you should be able to: • Define group velocity and explain how it differs from phase velocity xplain why the group velocity is also called the Explain why the group velocity is also called the energy transport velocity • Explain why signals are distorted in dispersive systems • Estimate signal dispersion ECSE 352 3.7-3 Contents • Dispersive materials • Introduction to group velocity • Relationship between group velocity and signal ispersion dispersion • Definition of energy transport velocity Estimation of signal dispersion Em fg p ECSE 352 3.7-4
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Origins of material dispersion • Dielectrics: E-field causes ound charges to oscillate E x + - bound charges to oscillate Æ damping loss –Mode l w i th complex permittivity dielectric '" • Due to resonances, the real t f th itti it i t c j εε ε part of the permittivity is not constant – See appendix D for details ECSE 352 3.7-5 Refractive index vs. Frequency Infrared Visible Ultraviolet r n = 1 ω ω 01 ω 02 ω 03 0 • In visible range d n /d ω is positive normal dispersion • Near resonance d n /d ω is negative anomalous dispersion ECSE 352 3.7-6 Refractive index of common optical materials* ense flint glass tion 1.7 Dense flint glass ex of refrac t 1.6 Light flint glass Ind e 1.5 Crystal quartz Borosilicate crown glass 1.4 Acrylic plastic Vitreous quartz ECSE 352 3.7-7 Wavelength (nm) 0 200 400 600 800 1000 *From: Hecht, Optics (2nd Ed.) p. 62 Dispersing prism R O Y G n( ω ) B
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/14/2011 for the course ECSE 352 taught by Professor Mi during the Fall '10 term at McGill.

Page1 / 7

Lect 3.7 - Department of Electrical and Computer...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online