Photonic Ceramics

EBB 443-Technical Ceramics

Dr. Sabar D. HutagalungSchool of Materials and Mineral Resources EngineeringUniversiti Sains Malaysia

Introduction

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 composition of the materials, nature, types of phases and interfaces present within the material and between the

material and its ambient media.

Introduction

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 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 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.

Th

e e

lectr

om

ag

neti

c

sp

ectr

um

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.

Dielectric Mirrors

Optical filters 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 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

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

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

z

Direction of Propagation

By

z

x

y

k

An electromagnetic wave is a travelling wave which has timevarying electric and magnetic fields which are perpendicular to eachother and the direction of propagation, z.

© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

Polarizer 1

TA 1

Polarizer 2 = Analyzer

TA 2

Light detectorE

Ecos

Unpolarized light

Linearlypolarized light

Randomly polarized light is incident on a Polarizer 1 with a transmission axis TA1. Lightemerging from Polarizer 1 is linearly polarized with E along TA 1, and becomes incidenton Polarizer 2 (called "analyzer") with a transmission axis TA2 at an angle to TA 1. Adetector measures the intensity of the incident light. TA1 and TA 2 are normal to the lightdirection.

© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

Polarization There are several different types of polarization:

Linear Circular, Elliptical and Partial.

Linear polarization occurs ehen EM waves always have the same orientation with direction of propagarion.

Circular polarization 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.

E

y

x

Exo = 0Eyo = 1 = 0

y

x

Exo = 1Eyo = 1 = 0

y

x

Exo = 1Eyo = 1 = /2

E

y

x

Exo = 1Eyo = 1 = /2

(a) (b) (c) (d)

Examples of linearly, (a) and (b), and circularly polarized light (c) and (d); (c) isright circularly and (d) is left circularly polarized light (as seen when the wavedirectly approaches a viewer)

© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

Elliptical polarization Elliptical polarization occurs when one particular

angle is preferred over the others for for transmission of energy.

Also, can be right- or left-polarized.

E

y

x

Exo = 1Eyo = 2 = 0

Exo = 1Eyo = 2 = /4

Exo = 1Eyo = 2 = /2

y

x

(a) (b)E

y

x

(c)

(a) Linearly polarized light with Eyo = 2Exo and = 0. (b) When = /4 (45 ), the light isright elliptically polarized with a tilted major axis. (c) When = /2 (90 ), the light isright elliptically polarized. If Exo and Eyo were equal, this would be right circularlypolarized light.

© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)

Electro-optic Materials

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

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.

Double Refraction In isotropic materials (glass), the induced 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

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 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)

Transparent Electro-optic ceramics

Electro-optic ceramic wafers

A variety of thin films, such as PLZT, PMN-PT, BaTiO3, BaSrTiO3, YIG, PBN, ITO and ZnO, has been developed.

Free Standing Electro-optic Film