Download Electro-Optic Ceramics

Photonic Ceramics
EBB 443-Technical Ceramics
Dr. Sabar D. Hutagalung
School of Materials and Mineral Resources Engineering
Universiti Sains Malaysia
Introduction
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There are a number of ways in which quanta of
light (photons) can interact with crystalline
ceramics and amorphous glassess.
The type of photon interactions that occur
depend considerably upon the
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composition of the materials,
nature,
types of phases and
interfaces present within the material and between the
material and its ambient media.
Introduction
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The incident radiant flux of photons is split into
beams of reflected, transmitted, absorbed, and
scattered radiation,
+++=1
where  = coefficient of total reflectance,  =
coefficient of total transmittance,  = coefficient
of total scattering,  = coefficent of absorption.
Radiation
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Photonic interactions with materials depend on
the frequency of the incident radiation.
Photons are quanta with energy E = h = hc/
Photons interact with electrons, ions, and
molecules of the material, which also have
characteristic energy level.
The magnitude and character of reflected
radiation depends upon the
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quality of the interface (roughness) and
angle of incidence
difference between the refractive indices of medium and glass or
ceramic and
the wavelength of radiation.
The electromagnetic spectrum
Dielectric Mirrors
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A dielectric mirror consists of a stack of
dielectric layers with n1<n2.
The thickness each layer is a quarter of
wavelength (layer/4)
layer is the wavelength of light in that layer,
or
o/n in which o is the free space wavelength
at which the mirror is required to reflect the
incident light, and
n is the refractive index of the layer.
Optical filters
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Absorption of specific wavelengths is used to
filter portions of the optical spectrum.
There are many different types of optical filter.
The 3 most common classifications are:
 Neutral filters,
 Polarizers, and
 Color filters
Optical filters
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Neutral filters are filters that transmit equally
across a broad bandwidth, and
 appear brown or grey.
Polarizers are used to filter out photons of a
given polarization or orientation.
Color filters are used to transmit selectively
light of certain frequency or bandwidth with a
minimum of attenuation.
Optical filters
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Neutral filters can attenuate light by reflection,
absorption, scattering, polarization, or a
combination of these methods.
Polarizing filters offer the advantage of
reduction the amount of heating of the filter.
Polarizing filters typically make use of material
such as CaCO3.
Polarization
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Light is composed of EM waves which oscillate in
directions perpendicular to the direction of
propagation of the light.
Normally, the orientation of these wave about the
propagation direction is random.
However, in some circumstances, these oscillations
become ordered in time.
This is called polarization.
Normal light is consequently called unpolarized.
Ex
Direction of Propagation
k
x
z
z
y
By
An electromagnetic wave is a travelling wave which has time
varying electric and magnetic fields which are perpendicular to each
other and the direction of propagation, z.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
Ecos
Linearly
polarized light
E

TA 2
Light detector
TA 1
Polarizer 2 = Analyzer
Polarizer 1
Unpolarized light
Randomly polarized light is incident on a Polarizer 1 with a transmission axis TA 1. Light
emerging from Polarizer 1 is linearly polarized with E along TA1, and becomes incident
on Polarizer 2 (called "analyzer") with a transmission axis TA 2 at an angle to TA1. A
detector measures the intensity of the incident light. TA 1 and TA2 are normal to the light
direction.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
Polarization
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There are several different types of polarization:
Linear
 Circular,
 Elliptical and
 Partial.
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Linear polarization occurs ehen EM waves
always have the same orientation with direction
of propagarion.
Circular polarization
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Circular polarization is a condition wherein the plane in
which the EM waves oscillate rotates about the direction
of propagation.
It can be either right-polaried or left-polarized, depending
on direction of rotation of EM oscillations.
y
y
(a)
y
(b)
(c)
=0
=1
=0
(d)
E
x
x
Exo
Eyo
y
=1
=1
=0
Exo
Eyo
=1
=1
 = /2
Exo
Eyo
x
E
=1
=1
 = /2
Exo
Eyo
Examples of linearly, (a) and (b), and circularly polarized light (c) and (d); (c) is
right circularly and (d) is left circularly polarized light (as s een when the wave
directly approaches a viewer)
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
x
Elliptical polarization
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Elliptical polarization occurs when one particular
angle is preferred over the others for for
transmission of energy.
Also, can be right- or left-polarized.
y
y
(a)
(b)
y
=1
=2
=0
E
x
x
Exo
Eyo
(c)
E
=1
=2
 = /4
Exo
Eyo
x
=1
=2
 = /2
Exo
Eyo
(a) Linearly polarized light with Eyo = 2Exo and  = 0. (b) When  = /4 (45), the light is
right elliptically polarized with a tilted major axis. (c) When  = /2 (90), the light is
right elliptically polarized. If Exo and Eyo were equal, this would be right circularly
polarized light.
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
Electro-optic Materials
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The electro-optic effect is the change in the
refractive index as a function of an externally applied
electric field.
In unisotropic materials the index of refraction
depends on the direction of propagation and the
direction of polarization of the light.
This means that the two components of light
polarization can propagate at a different speed inside
the material.
This in turn causes a rotation of the overall
polarization direction.
Electro-optic Materials
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By placing the electro-optic material between
two polarizers one can control the amount of
light passing through by changing the voltage.
To appreciate properly how electro-optic
ceramics function, it is first necessary to
consider the nature of light and its interaction
with dielectrics.
 In isotropic
materials (glass), the induced
Double
Refraction
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electric polarization is always parallel to the
applied electric field
In anisotropic materials, the polarization
depends on both the direction and the
magnitude of the applied field
Di = ij Ej
• The phase velocity of EM wave depends on
both its polarization and its direction of
propagation
Light propagates at a speed depending on the
orientation of its plane of polarization relative
to the crystal structure
Electro-optic Applications
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The requirements for using ferroelectric thin
films for electro-optic applications include an
optically transparent film with a high degree of
crystallinity.
The electro-optic thin film devices are of two
types; one in which the propagation of light is
along the plane of the film (optical
waveguides) and the other in which the light
passes through the film (optical memory and
displays).
Electrooptic Ceramics Based Light
Modulators
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Electrooptic ceramic light modulators provide a
superior alternative to liquid crystal and electrooptic
single crystal based optics.
The most popular materials
 PLZT (La modified lead zirconate titanate)
 BST (BaSrTiO3)
 PSN (lead scandium niobate)
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Electro-optic ceramic
wafers
Transparent
Electro-optic
ceramics
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Free Standing
Electro-optic Film
A variety of thin
films, such as PLZT,
PMN-PT, BaTiO3,
BaSrTiO3, YIG, PBN,
ITO and ZnO, has
been developed.