physics

1. TOPIC-OPTICAL FIBRE
PHYSICS
(2110011)
GUIDED BY:-
MEDHA MAM

2. An optical fiber (or optical fibre) is a flexible, transparent
fiber made by drawing glass (silica) or plastic to a diameter
slightly thicker than that of a human hair.[1] Optical fibers are
used most often as a means to transmit light between the
two ends of the fiber and find wide usage in fiber-optic
communications, where they permit transmission over
longer distances and at higher bandwidths (data rates) than
wire cables. Fibers are used instead of metal wires because
signals travel along them with lesser amounts of loss; in
addition, fibers are also immune to electromagnetic
interference, a problem from which metal wires suffer
excessively.

3.  Immunity to Electromagnetic Interference
Data Security
 Non Conductive Cables
Eliminating Spark Hazards
 Ease Of Installation
High Bandwidth Over Long Distances

4. Total internal reflection is a phenomenon which
occurs when a propagating wave strikes a medium
boundary at an angle larger than a particular critical
angle with respect to the normal to the surface. If
the refractive index is lower on the other side of the
boundary and the incident angle is greater than the
critical angle, the wave cannot pass through and is
entirely reflected. The critical angle is the angle of
incidence above which the total internal reflection
occurs.

6. The Numerical Aperture (NA) is a measure of how much light can be
collected by an optical system such as an optical fibre or a microscope
lens.
The NA is related to the acceptance angle a, which indicates the size
of a cone of light that can be accepted by the fibre.
cladding
n1
n2
core
n2
cladding
air
a
n2
n1
core
Both numerical aperture and acceptance angle are linked to the refractive index via:
NA = naSin a = (n1
2 – n2
2)1/2
Where n1 = refractive index of core
n2 = refractive index of cladding
na = refractive index of air (1.00)

7. One way of measuring the NA of this fibre is to fill the fibre with
light and measure the characteristics of the light leaving the
fibre. Plug the fibre into the analog output and position the
components on the optical bench as shown in figure.
a
screen
Analog in BNC & LEDAnalog out Photodiode
1
Photodiode 2 BNC & LED
Fibre
The fibre output is a cone of light that spreads out wider as the
distance from the fibre exit increases.
The grid slide or screen and ruler can be used to measure
diameters. The edges of the cone of light may appear fuzzy so
there will be an error introduced into your measurements.
Measurement of the edges is an approximation to the notion of
Full Width Half Maximum (FWHM). This is how light boundaries
are characterised .

8. There are 2 types of propagation mode in fiber optics cable which
are multi-mode and single-mode. These provide different
performance with respect to both attenuation and time dispersion.
The single-mode fiber optic cable provides the better performance
at a higher cost.
The number of modes in a fiber optic cable depends upon the
dimensions of the cable and the variation of the indices of refraction of
both core and cladding across the cross section. There are three
principal possibilities which are multi-mode step index, single-mode
step index and multi-mode graded index.

9. There are three types of
fiber optic cable commonly
used: single
mode, multimode and
plastic optical fiber (POF).
Transparent glass
or plastic fibers which
allow light to be guided
from one end to the other
with minimal loss.

10. THANK YOU
PREPARED BY:-
MOHIT TALREJA
151080106028
CIVIL