1. Satish Pradhan Dnyanasadhana college, Thane
Subject-APPLIED Physics paper-III
Class- S. Y. B. Sc.
SEM-III
TOPIC FIBRE OPTICS
Presented By
Ms. Namrata A. Singh
Dept. of Physics

3. INTRODUCTION
Fibre optic communications has revolutionised the telecommunications industry. It has also made its presence widely felt within the data network community as well. Using fibre optic cable, optical communications have enabled telecommunications link to be made over much greater distances and with much lower levels of loss in transmission medium and possibly most important of all, fibre optical communications has enabled much higher data rates to be accommodated.
As a result of these advantages, fibre optic communications systems are widely employed for applications ranging from major telecommunications backbone infrastructure to Ethernet systems, broadband distribution and general distribution networking.

4. Evolution of optical fibre
Alexander Graham Bell
patents on tubing
patent for two-layer glass wave guide
Laser first used as light source
High loss of light discovered
1970s - Refining of manufacturing process
1980s - optical fibre technology becomes backbone of
long distance telephone networks in numerical aperture.

5. What is optical fibre ?
An optical fibre is a flexible, transparent fibre made of high quality
glass (silica) or plastic slightly thicker than a human hair
It either functions as a waveguide or light pipe that transmits data between
two ends of the fibre or fibre cable
Optical fibre are widely used in fibre-optic communications which permits
data over long distances and at higher bandwidths (data rates) than other
forms of communication
Fibres are used instead of metal wires because signals travel along them with
less loss and are also safe to electromagnetic interference
The field of applied science and engineering concerned with the design and
application of optical fibres is known as fibre optics

6. Structure of optical fibre
Optical fibre is comprised of a light carrying core surrounded by cladding which
traps the light in the core by the principle of total internal reflection.
The core and cladding are usually fused silica glass which is covered by a plastic
coating called the buffer plastic coating which protects the glass fibre from
physical damage , moisture and mechanical shocks. It also gives strength and
safety

7. Light propagation through fibre
core
cladding
light
Fig.(1) An optical fibre carrying light

8. The Numerical apertureΦ Φ Φ Φ
Cladding n2
Air
n0=1
core  n1 r
axis of the fibre i
incident
ray
Fig.(2) Propagation of light through fibre at the
angle of acceptance

9. Step-Index optical fibre
Fig.3(b) Propagation of light through
an step-index fibre
Fig.3(a) step-index fibre

10. Graded-Index optical fibre
Fig.4(b) Propagation of light
through graded-index fibre
Fig.4(a) Graded-index optical fibre

11. Applications of Fibre optics
a) Fibre optics communication
Fig.5(a) A typical communication system

12. optical fibre
Fig.5 (b )Point-to-point communication link using
optical fibre

13. Fig.6 : A fiber optic temperature sensor
b) Fiber Optic Sensor
Reflecting
mirror
Light source
Silicon
layer
Detector
Fig.6 : A fiber optic temperature sensor

14. Advantages of optical communication
Capacity of carrying information is very large and have a wider bandwidth
They have a very low transmission loss
Optical fibres are very light in weight ,flexible, smaller in size, this makes them
more suitable in spaceships and aircraft
Glass fibres can withstand high temperature. Temperature approaching 8000C
leaves glass fibre unaffected
Communication by means of an optical fibre provides a high degree of security
and privacy
Also, practically there is no crosstalk, any interference or coupling with other
communication channel. any electrical noise do not interfere with propagation
of light signals because of dielectric nature of optical fibre

15. Application of optical fibre in medical field

16. a. cladding b. armor c. shielding d. cover
MCQs
It refers to the dielectric material of an optical fiber that surrounds the core.
a. cladding b. armor c. shielding d. cover
Light propagation through an optical fiber is based on the principle of total
a. internal reflection b. external reflection c. internal refraction d. internal refraction
For total internal reflection, angle of incidence of the ray at the interface of core-cladding must be ________ than critical angle of same interface.
a. less than b. equal to c. greater than d. none of these
In ______ optical fiber core and cladding is of uniform refractive index.
a. step-index b. graded-index
The maximum angle with which a ray of light can enter through the entrance end of the fiber and still be totally internally reflected is called _________
a. angle of acceptance b. numerical aperture c. critical angle
In graded-index optical fiber , a core has _______ refractive index.
a. uniform b. non-uniform

17. a. reflection b. refraction c. refraction d. dispersion
MCQs
In the structure of fiber, the light is guided through the core due to total internal _______
a. reflection b. refraction c. refraction d. dispersion
In the structure of fiber, which component provides additional strength and prevents
the fiber from any damage ?
a. core b. cladding c. buffer coating d. none of these
In an optical fiber, the concept of Numerical aperture is applicable in describing the ability of_________
a. Light collection b. Light scattering c. Light polarization d. Light dispersion
In the structure of fiber optic cable, the refractive index of core is always _____ the
refractive index of cladding.
a. less than b. equal to c. greater than d. none of these
Which among the following characteristics of Laser light specifies the precise movement of all individual light waves together through time and space /
a. monochromatic b. directional c. coherent d. brightness

18. Assignment Problems
Determine: a) the critical angle of reflection for core-cladding boundary and
b) the acceptance angle of the fibre
Given : Refractive index of core is 1.4
Refractive index of cladding is 1.3
[ Ans: 68.21o , o ]
Calculate the numerical aperture of a step index fibre for an optical fibre that have
a core of refractive index 1.5 and cladding of index 1.48.Also determine the
maximum angle for entrance of light if the fibre is put in the air.
[ Ans: NA: , im = ]
The core and cladding of an optical fibrd has refractive indices 1.5 and 1.47
respectively .Find the acceptance angle in air and the critical angle for
core/cladding interface.
[ Ans: 17o27’,c=78o30’]