Optical fibers communicatiobyom

Prof.Byomakesh Mahapatra
Assistant Professor
University of Bombay
Prof. Byomakesh Mahapatra

People behind OFC Development
Holger Møller Hansen in his workshop.
Courtesy Holger Møller Hansen
Heinrich Lamm as a German
medical student in 1929, about the time
he made the first bundle of fibers to
transmit an image. Courtesy Michael
Lamm

Brian O’Brien, who suggested
that cladding would guide light along fiber.
Charles K. Kao making optical
measurements at Standard
Telecommunications Laboratories

General and Optical Communication systems

Need for Fiber Optical Communication
Increase of the
bandwidth and
decreases of the cost
per transmitted bit for
optical communication
systems during the
1990‘s.

Different frequency range:-

Different frequency range:-
EHz:-Exahertz
PHz :- Petahertz

The Electromagnetic Spectrum
Shortest wavelengths
(Most energetic photons)
Shortest wavelengths
(Most energetic photons)
EE == hhnn == hhcc//ll
h = 6.6x10-34 [J*sec]
(Planck’s constant)
Longest wavelengths
(Least energetic photons)
Longest wavelengths
(Least energetic photons)

Properties of light:-
There are three theories are used to explain light:
Ray theory
Wave theory
 Quantum theory

Properties of light/ important terms:-
Refraction
Reflection
Refractive index
Ray theory
Total internal reflection
 Geometrical optics
Related to optical fiber
Absorption
propagation loss
Dispersion
scattering
Optical wave guide
Wave
Wave front
propagation
Isotropic medium
Plane wave
polarization

Ray theory:-
It state that light is a stream minute particles and travel in a straight line .
A beam of light is a group of rays called as ray congruence.
A ray is the is the thinnest pencil of light with a well defined boundaries with
out diffraction.
aperture
Light patch

Wave theory of light :-
Light is considered as an electromagnetic radiation. It
consists of two components i.e., the electric component and
the magnetic component which oscillate perpendicular to
each other as well as to the direction of path of radiation.
It propagates in a particular direction according to this E&H
components knoPwrofn. B yaomsa kepsho Mlaahrapizatraa tion.

Quantum theory:-
Max Planck proposed Quantum theory by considering light to possess
particle nature.
1) Energy is emitted due to vibrations of charged particles in the black
body.
2) The radiation of energy is emitted or absorbed discontinuously in the
form of small discrete energy packets called quanta.
3) Each quantum is associated with definite amount of energy which is
given by the equation E=hν.
Where
h = planck's constant = 6.625 x
10-34 J. sec = 6.625 x10-27 erg.
sec
ν= frequency of radiation

Quantum theory:-
4) The total energy of radiation is quantized i.e., the total energy is
an integral multiple of hν. It can only have the values of 1 hν or 2
hν or 3 hν. It cannot be the fractional multiple of hν.
5) Energy is emitted and absorbed in the form of quanta but
propagated in the form of waves.
Photo electric effect

There was a problem with wave theory
In the early 20th century, several effects were observed which could not be
understood using the wave theory of light.
Two of the more influential observations were:
1) The Photo-Electric Effect
2) The Compton Effect

Photoelectric Effect (I)
electrons
emitted ?
No
Yes, with
low KE
Yes, with
high KE
“Classical” Method
Increase energy by
increasing amplitude
electrons
emitted ?
No
No
No
No
No electrons were emitted until the frequency of the light exceeded
a critical frequency, at which point electrons were emitted from
the surface! (Recall: small l  large n)

Reflection:-
Normal
Incident ray Reflected rays
Angle of
incidence
Angle of
reflection
Mirror
Mirror

The Law of Reflection:-
Angle of iinncciiddeennccee == AAnnggllee ooff rreefflleeccttiioonn
In other words, light gets reflected from a surface at ____ _____
angle it hits it.
The same !!!
same

Refraction:-
Refraction is when waves ____ __ or slow down
due to travelling in a different _________. A
medium is something that waves will travel
through. When a pen is placed in water it looks
bent from the normal position.
In this case the light rays are slowed down by the
water and are _____, causing the pen to look odd.
The two mediums in this example are ______ and
_______.
Words – speed up, medium, bent, water, air,

Refraction:-

Ex:-
Light banding due to refraction

Snell’s Laws
 Snell's law gives the relationship between angles of
incidence and refraction for a wave impinging on an interface
between two media with different indices of refraction. The
law follows from the boundary condition that a wave be
continuous across a boundary, which requires that the phase
of the wave be constant on any given plane.

Refractive index :-
The ratio of speed of light in vacuum to that in
matter is the index of refraction (n)
n = c/v where
c = speed of light in vacuum and
v = speed of light in the medium
Refractive index of air: 1.0003
water: 1.33
glass: 1.4 – 1.7
silicon : 3.96
GaP : 3.5
Gas :3.9
diamond :2.41
LiNbO3 :2.21

Total Internal Reflection:-
When there is a change the incident angle of the light on the block, the
reflected light varies. At a certain angle, called the critical angle all the
light is reflected, and none is refracted. When this happens we have total
internal reflection.
TIR in optical fiber

Geometrical optics
Geometrical optics, or ray optics, describes light propagation in terms of "rays".
It include all the ray properties of the light like reflection ,refraction and
corresponding optics lenses polarizer, mirror etc
The "ray" in geometric optics is an abstraction, or "instrument", which can be used
to approximately model how light will propagate.

Geometrical optics

Absorption:-
When light enter some of its energy is dissipated as heat energy and
loose some of its intensity.
When the absorption of energy occur selectively for a certain wave length
the wave length only reflected which are not absorbed.

Dispersion:-
When the light ray passes through a prism it is separate in to a ray of constituent
color this phenomenon is known as dispersion.
It can also be define as the broadening of the light plus in an optical wave
propagation
 in an optical fiber there are different kind of dispersion is phenomenon is found
Material dispersion
Wave guide dispersion
Material dispersion:-It
occur due to the varying material properties
which provide different velocity to the light in
an optical fiber.
Intermodal or chromatic dispersion
Polarization mode dispersion

Fiber Dispersion
Waveguide dispersion
- Waveguide dispersion occurs because the mode propagation
constant is a function of the size of the fiber's core relative to the
wavelength of operation.
– Waveguide dispersion also occurs because light propagates
differently in the core than in the cladding.
Polarization Mode Dispersion
Polarization mode dispersion (PMD) occurs when different
planes of light inside a fiber travel at slightly different speeds, making it
impossible to transmit data reliably at high speeds(multimode fiber)
Total Dispersion
– Total dispersion is due to all types of dispersion
Δt tot=Δt
2modΔt
2chromΔt
2pol

Modal dispersion

Scattering:-
•Scattering can be broadly defined as the redirection of radiation out of the
original direction of propagation, usually due to interactions with molecules
and particles
• Reflection, refraction, diffraction etc. are actually all just forms of scattering
• Matter is composed of discrete electrical charges (atoms and molecules –
dipoles)
• Light is an oscillating EM field – excites charges, which radiate EM waves
• These radiated EM waves are scattered waves, excited by a source
external to the scattered
• The superposition of incident and scattered EM waves is what is observed
rainbow

Scattering geometry
Backward scattering Forward scattering
(backscattering)

What is Rayleigh scattering?
(or why is the sky blue)
The shorter the wavelength, the
more light is scattered
 blue is scattered more than red.
 this is why the sky is blue and
sunsets are red.
Think of white light from
sun as a mixture of R,
G and B
Blue is scattered
the most so sky
looks blue when
we look away from
the sun
For same reason
sun looks yellow
(red + green)
More atmosphere
allows next
shortest
wavelengths
(green) to scatter
so sunset looks
red Prof. Byomakesh Mahapatra

Optical wave guide
An optical waveguide is a physical structure that guides electromagnetic
waves in the optical spectrum. Common types of optical waveguides include
optical fiber and rectangular waveguides.
Optical waveguides are used as components in integrated optical circuits or as
the transmission medium in local and long haul optical communication systems
Rectangular Different type of waveguides waveguides

Wave front:-
a wavefront is the locus of points having the same phase a line or curve in 2d, or
a surface for a wave propagating in 3d
In an optical system the wave front can be describe by simple maxuall equation
 The general wave front of any light source is the spherical wave front, but when
the radius of this spherical is very large then this can be evaluated by the simplest
form of a wavefront is known as the plane wavefront, where the rays are parallel to
one another

Wave polarization:-
Polarization is a property of waves that can oscillate with more than one
orientation
The polarization of light is described by specifying the orientation of the wave's
electric field at a point in space over one period of the oscillation. When light travels in
free space, in most cases it propagates as a transverse wave—the polarization is
perpendicular to the wave's direction of travel. In this case, the electric field may be
oriented in a single direction (linear polarization), or it may rotate as the wave travels
(circular or elliptical polarization). In the latter case, the field may rotate in either
direction

x
Looking at ray "head-on" see
green arrows up & down
y
z
x
y
z
Light is polarized if the waveform
and electric force field arrows
remains in the same plane
The electric force arrows must always
be perpendicular to the ray
This is a light ray traveling in the z-direction
and polarized in the y-direction
Here is a light ray traveling in the
same direction but polarized in the
x-direction
We will visualize the polarization in
the x-y plane, looking at rays head-on
The white force arrows point up and
down or left and right, stacked up
behind one-another.
Here is the convention for
visualizing vertical and horizontal
polarization
y
x
What is polarized light?

Optical fibers communicatiobyom

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