This document discusses key concepts in optical fibers including total internal reflection, acceptance angle, and numerical aperture. It defines total internal reflection as how light propagates through the fiber using refraction at the core-cladding interface. The acceptance angle is the maximum angle of incidence for light entering the fiber. Numerical aperture is a figure of merit used to describe the light gathering ability of a fiber, defined as the sine of the acceptance cone half angle or the normalized refractive index difference between core and cladding.

1. .
TOTAL INTERNAL
REFLECTION,
ACCEPTANCE ANGLE
AND
NUMERICAL
APERTURE.

2. PRESENTED BY:
ROLL NO. NAME ENROLL
NO.
1) 46 PRAJAPATI RIYA P.
150860106054
2) 47 BARIA VAISHNAVI Y.
150860106004
3) 48 PATEL MARTINA R.
150860106045
4) 49 PATEL TIRTH H.
150860106070

3. OPTICAL FIBRE
 Optical fibre is made from thin strands of either
glass or plastic
 It has little mechanical strength, so it must be
enclosed in a protective jacket
 Often, two or more fibers are enclosed in the
same cable for increased bandwidth and
redundancy in case one of the fibers breaks
 It is also easier to build a full-duplex system
using two fibers, one for transmission in each
direction

4. TOTAL INTERNAL REFLECTION
 The transmission of light in an optical fibre involves the
phenomena of total internal reflection at the interface
between the core and cladding.
 When light enters one end of the glass fibre under right
conditions, most of the light will propagate or move down
the length of the fibre and exit from the far end.
 A small part of the light will escape through the side wall
of the fibre, and some will also be lost due to internal
absorption.
 But, a portion of the light will be contained and guided to
the far end.
 Such a fibre is called a “light pipe” or “light guide”.

5. CONDITIONS FOR TOTAL INTERNAL REFLECTION WITHIN FIBER
WALL
 The refractive index n1 of the core must always be
greater than the refractive index n2 of the cladding.
 The light must approach the wall with an angle of
incidence Ø that is greater than the critical angle
Øc.
SinØc=n2/n1
(when Ø = Øc,
then by snells law,
n1 sinØc=n2 sin90 or sinØc=n2/n1)

6. REFRACTION AND TOTAL INTERNAL
REFLECTION.

7. ACCEPTANCE ANGLE
Definition :Acceptance angle
Acceptance angle of fiber Ømax is defined as the maximum
value of angle of incidence at the entrance(air/fiber interface)
end of the fibre, at which the angle of incidence at the core-
cladding interface is equal to critical angle of the core medium.
Mathematically given as
Where n1 and n2 are the refractive index of the core and
cladding respectively.

8. NUMERICAL APERTURE OF OPTICAL FIBER
Numerical aperture (NA) is a figure of merit that is used to
describe the light gathering or light collecting ability of an optical
fiber. The large magnitude of (NA),the greater the amount of light
accepted by the fibre from the external light source.
Numerical aperture is mathematically define as the sine of the
acceptance cone half angle.
Thus,

9.  The NA can also be expressed in term of normalized
refractive index difference or relative refractive index(
).
 It is defined as the ratio of refractive index difference
between core and cladding to the refractive index of
core