Photonic crystals are periodic structures in optical media that exhibit unique optical dispersion properties and create photonic band gaps, which prevent certain wavelengths of light from propagating. They differ from semiconductors in their control of electromagnetic wave propagation and are categorized into one, two, and three-dimensional structures. Applications include low-threshold lasers, improved optical devices, and medical technologies, indicating a significant potential for future use in various fields.

1. PHOTONIC
CRYSTALS
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2. CONTENTS
O CRYSTAL
O SEMICONDUCTOR
O PHOTONIC CRYSTAL
O PHOTONIC BAND GAP
O TYPES
O APPLICATIONS
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3. What is a crystal?
O A homogeneous solid formed by repeating,
Three dimensional pattern of atoms, ions, or
molecules.
O These have fixed distances between
constituent parts. (from Greek krustallos).
PHOTON:
The quantum of electromagnetic
energy, having zero mass, no electric charge,
and long lifetime.
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4. What is a semiconductor?
O It is a type of crystal whose
conductivity is in between a conductor
and insulator.
Examples: Silicon Germanium
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5. What is a photonic crystal?
O A photonic crystal is a periodic
structure in an optical medium, which
structure creates unusual optical
dispersion properties
OR
O Crystals having photonic band gap are
called photonic crystals or photonic
band gap crystals.
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6. Examples
O Examples in nature which reflect
electromagnetic radiation as
propagation through them is
prohibited.
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7. Natural opals
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8. Artificial Opal
Artificial opal sample (SEM Image)
Several cleaved planes of fcc structure are shown9/15/2017SHAREEF 8

9. What is Photonic Band Gap?
O Photonic band gap a range of forbidden
frequencies within which a specific
wavelength is blocked, and light is reflected
rather than transmitted.
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10. Basics of photonic band gaps
O The behavior of light in a photonic
crystal is similar to the movement
of electrons and holes in a
semiconductor.
O If the periodicity of the lattice is
broken by a missing Si atom or
by various impurity an electron
can have enough energy to be
in the band gap.
O The same for photons in a
photonic lattice, photons move
in a transparent dielectric
material that contains tiny air
holes arranged in a lattice
pattern.
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11. Bragg Reflection
2 ( )B Bnd Sin  
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12. Differences b/w
semiconductors &PBGC
Semiconductors
O Periodic crystal potential
O Atomic length scales
O Crystal structure given by nature
O Control electron flow
O 1950’s electronic revolution
PBG Crystals
O Periodic variation of dielectric
constant
O Length scale ~ 
O Man-made structures
O Control e.m. wave propagation
O 1990’s optical fibers, lasers,
PBGs --> photonics era
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13. What are different types of
PBGS?
O Periodic structure in an optical medium,
can be periodic in
O Single dimension
O Two dimensions
O Three dimensions.
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14. One Dimensional PBGC
O The material is periodic in the z-
direction, and homogeneous in the x y-
plane.
O Light propagate only in the z-direction
through 3 different 1d lattice samples.
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15. Two Dimensional PBGC
O The material has periodicity in 2
dimensions (that's where the photonic
gaps appear) and is homogeneous in
the third dimension.
O It periodic in the x y-plane and not in
the z-direction as for the 1d lattice.
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16. Three Dimensional PBGC
O A three-dimensional photonic crystal was
created using layer-by-layer periodic
structure method.
O The orientations of the axes are rotated by
90o between adjacent layers.
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17. Applications
O Suppression of spontaneous emission
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18. Applications(contd.)
O Low-threshold lasers, single-mode
LEDs, mirrors, optical filters
O Lasers and optical devices - improved
performance in efficiency and
reduction of background noise
O Fast electronics – inter chip
communication
O Medical and biological application
e.g., microwave resonance therapy (40-
80 GHz), imaging
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19. In fiber optic communication
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20. Conclusion
O Photonic crystals are going to be the
future semiconductors
O It has many applications irrespective of
fields
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