Photonic Ceramics

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Photonic Ceramics

• EBB 443-Technical Ceramics
• Dr. Sabar D. Hutagalung
• School of Materials and Mineral Resources
  Engineering
• Universiti Sains Malaysia

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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.

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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.

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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.

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The electromagnetic spectrum
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Dielectric Mirrors

• A dielectric mirror consists of a stack of
  dielectric layers with n1ltn2.
• 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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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).

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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)

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• Transparent Electro-optic ceramics

• Electro-optic ceramic wafers

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• 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