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Fig 9.1

Light is an electromagnetic wave

An electromagnetic wave is a traveling wave that has time-varying electric and magneticFields that are perpendicular to each other and the direction of propagation z .

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From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

E x = E o cos( t kz + )

E x = electric field along x at position z at time t,k = propagation constant , or wavenumber = 2 / = wavelength = angular frequency

E o

= amplitude of the wave

is a phase constant which accounts for the fact that at t = 0and z = 0 E x may or may not necessarily be zero depending onthe choice of origin.( t kz + ) = = phase of the wave .

This equation describes a monochromatic plane wave of infinite extent traveling in the positive z direction.z

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Fig 9.2From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

A plane EM wave traveling along z , has the same E x (or B y) at any point in a given xy plane.All electric field vectors in a given xy plane are therefore in phase. The xy planes are of Infinite extent in the x and y directions.

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Fig 9.3From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Wavevector

A traveling plane EM wave along a direction k .

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Fig 9.6From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Refractive index n and the group index N g of pure SiO 2 (silica) glass as a function of wavelength.

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Fig 9.8From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

A light wave traveling in a medium with a greater refractive index ( n1 > n2) suffersreflection and refraction at the boundary.

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Fig 9.9

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Light wave traveling in a more dense medium strikes a less dense medium. Depending onThe incidence angle with respect to qc, which is determined by the ratio of the refractiveIndices, the wave may be transmitted (refracted) or reflected.(a) i < c(b) i = c(c) i > c and total internal reflection (TIR).

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Fig 9.12

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

ernal reflection:Magnitude of the reflection coefficients r // and r vs. angle of incidence i for n1 = 1.44 and

= 1.00. The critical angle is 44 .The corresponding changes // and vs. incidence angle.

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Fig 9.13

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

The reflection coefficients r // and r versus angle of incidence i for n1 = 1.00 and n2 = 1.44.

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Fig 9.14

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

E v a n e s c e n t

w a v e

W a v e f r o n t

I n c i d e n t

w a v e

E r ,

y

E r , n2

n1

> n2

E r , E r ,

E v a n e s c e n t

w a v e

R e f l e c t e d

w a v e

k r

When i > c, for a plane wave that is reflected, there is an evanescent wave at the boundary propagating along z .

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Fig 9.20

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Complex Refractive Index and Reflectance

(a) Refractive index and extinction coefficient vs. normalized frequency, / 0.(b) Reflectance vs. normalized frequency

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Fig 9.23

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Absorption coefficient versus wavelength for various semiconductors.SOURCE: Data selectively collected and combined from various sources.

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Fig 9.24

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Electron energy ( E ) vs. crystal momentum k and photon absorption. (a) Photon absorption in adirect bandgap semiconductor. (b) Photon absorption in an indirect bandgap semiconductor (VB,valence band; CB, conduction band)

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Fig 9.26

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Attenuation in optical fibers

Illustration of typical attenuation versus wavelength characteristics of a silica-based opticalfiber.There are two communications channels at 1310 and 1550 nm.

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Fig 9.28

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Photoluminescence

Photoluminescence: light absorption, excitation, nonradiative decay and light emission, andReturn to the ground state E 1.The energy levels have been displaced horizontally for clarity.

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Fig 9.31

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Polarization

A linearly polarized wave has its electric field oscillations defined along a line perpendicular he direction of propagation z . The field vector E and z define a plane of polarization.The E -field oscillations are contained in the plane of polarization.A linearly polarized light at any instant can be represented by the superposition of two fields

and E y with the right magnitude and phase.

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Fig 9.35

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

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Fig 9.38

From Principles of Electronic Materials and Devices, Third Edition , S.O. Kasap ( McGraw-Hill, 2005)

Birefringent Retarding Plates

A retarder plate.The optic axis is parallel to the plate face. The o- and e-waves travel in the same direction butat different speeds.

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Fig 9.43

From Principles of Electronic Materials and Devices Third Edition S O Kasap ( McGraw-Hill 2005)

Transverse Pockels cell phase modulator. A linearly polarized input light into an electro-optic

Crystal emerges as a circularly polarized light.