PHOTONIC CRYSTALS

PHOTONIC
CRYSTALS
9/15/2017SHAREEF 1

CONTENTS
O CRYSTAL
O SEMICONDUCTOR
O PHOTONIC CRYSTAL
O PHOTONIC BAND GAP
O TYPES
O APPLICATIONS
9/15/2017SHAREEF 2

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.
9/15/2017SHAREEF 3

What is a semiconductor?
O It is a type of crystal whose
conductivity is in between a conductor
and insulator.
Examples: Silicon Germanium
9/15/2017SHAREEF 4

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.
9/15/2017SHAREEF 5

Examples
O Examples in nature which reflect
electromagnetic radiation as
propagation through them is
prohibited.
9/15/2017SHAREEF 6

Natural opals
9/15/2017SHAREEF 7

Artificial Opal
Artificial opal sample (SEM Image)
Several cleaved planes of fcc structure are shown9/15/2017SHAREEF 8

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.
9/15/2017SHAREEF 9

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.
9/15/2017SHAREEF 10

Bragg Reflection
2 ( )B Bnd Sin  
9/15/2017SHAREEF 11

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
9/15/2017SHAREEF 12

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.
9/15/2017SHAREEF 13

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.
9/15/2017SHAREEF 14

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.
9/15/2017SHAREEF 15

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.
9/15/2017SHAREEF 16

Applications
O Suppression of spontaneous emission
9/15/2017SHAREEF 17

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
9/15/2017SHAREEF 18

In fiber optic communication
9/15/2017SHAREEF 19

Conclusion
O Photonic crystals are going to be the
future semiconductors
O It has many applications irrespective of
fields
9/15/2017SHAREEF 20

PHOTONIC CRYSTALS