Optical Fibres - Ray, Optics & Optical Instruments Video Lecture - Class 12 | Best Video for Class 12

optical fibers optical fibers are long
thin strands of very pure glass about
the diameter of a human hair they are
arranged in bundles called optical
cables and are used to transmit light
signals over long distances a single
optical fiber consists of three layers
namely core cladding and buffer coating
core is the thin glass center of the
fiber through which the light travels
cladding is the outer optical material
surrounding the core that reflects the
light back into the core buffer coating
is the plastic coating that protects the
fiber from moisture and from any kind of
external damage the bundles are
protected by the cables outer covering
called a jacket
how does an optical fiber transmit light
transmission of light through an optical
fiber is similar to the transmission of
light through a hallway when you have to
eliminate a long straight hallway you
just have to point the beam straight
down the hallway as light rays always
travel in a straight line
but to eliminate a hallway which is a
winding one with multiple bends you need
to line the walls with mirrors and angle
the beam so that it bounces from side to
side all along the hallway this is
exactly what happens in an optical fiber
optical fibers make use of total
internal reflection to confine light
within the core of the fiber the core of
an optic fiber has a higher refractive
index than the cladding and hence the
life suffers total internal reflection
although the cladding does not carry
light it is nevertheless an essential
part of the fiber the cladding is not
just a mere covering it keeps the value
of the critical angle constant
throughout the whole length of the fiber
propagation of light in an optical fiber
letter ray of light be incident on the
fiber making an angle theta-c
with the axis as shown here it gets
reflected into the fiber let the
refracted ray make an angle feature I at
the core and cladding interface if theta
I is greater than the critical angle
theta-c
then the Rays suffers total internal
reflection so all the energy in the ray
of light is reflected into the core and
none escapes into the cladding the ray
then crosses to the other side of the
core and because the fiber is more or
less straight the ray will meet the
cladding on the other side at an angle
which again causes total internal
reflection the ray is then reflected
across the core again in the same manner
in this way the line zigzags
its way along the fiber thus the light
gets transmitted to the end of the fiber
because the cladding does not absorb any
light from the core the light wave can
travel great distances however some of
the light signal degrades within the
fiber mostly due to impurities in the
class
terminology used in fiber optics here
you can see a ray of light traveling
from air of a refractive index mu zero
into an optic fiber the maximum angle of
incidence in air for which all the
incident light is totally reflected at
the interface of a pair of media having
refractive indices mu 1 and mu 2 is
called the angle of acceptance fiber
attenuation it is defined as the loss of
light energy during its transmission
through an optical fiber due to
absorption by the impurities in the
glass fiber
applications of optical fibers optical
fibers are used to transmit
communication signals in endoscope used
to investigate interior organs which
cannot be viewed directly and in photo
meters