GIRISH M
ASST . PR OF ESSOR
BRIEF FLOW OF CHAPTER
1. Introduction
2. What are Optical Fibers?
3. Evolution of optical fiber
4. Structure of optical fiber
5. Workings principle of optical fiber
6. Classification of optical fiber
7. Optical fiber communication system
8. Advantages / Disadvantages of Optical fiber
9. Applications of Optical fiber
10. Conclusion
EVOLUTION OF OPTICAL FIBER
• 1880 – Alexander Graham Bell
• 1930 – Patents on tubing
• 1950 – Patent for two-layer glass wave-guide
• 1960 – Laser first used as light source
• 1965 – High loss of light discovered
• 1970s – Refining of manufacturing process
• 1980s – OF technology becomes backbone
of long distance telephone networks in NA.
WHAT IS OPTICAL FIBER?
• An optical fiber is a hair thin cylindrical fiber of glass
or any transparent dielectric medium.
• The fiber which are used for optical communication
are wave guides made of transparent dielectrics.
• Its function is to guide visible and infrared light over
long distances.
STRUCTURE OF OPTICAL FIBER
• Core – central tube of very thin size made up of optically
transparent dielectric medium and carries the light form
transmitter to receiver. The core diameter can vary from
about 5um to 100 um.
• Cladding – outer optical material surrounding the core
having reflecting index lower than core. It helps to keep
the light within the core throughout the phenomena of
total internal reflection.
• Buffer Coating – plastic coating that protects
the fiber made of silicon rubber. The typical diameter of
fiber after coating is 250-300 um.
WORKING PRINCIPLE
Total Internal Reflection
• When a ray of light travels from a denser to a rarer
medium such that the angle of incidence is greater
than the critical angle, the ray reflects back into the
same medium this phenomena is called total
internal reflection.
• In the optical fiber the rays undergo repeated total
number of reflections until it emerges out of the
other end of the fiber, even if the fiber is bent.
THE ARROW AND THE BENT PENCIL
TOTAL INTERNAL REFLECTION IN
OPTICAL FIBER
CLASSIFICATION OF OPTICAL FIBER
• Optical fiber is classified into two categories based
on :-
1) The number of modes, and
2) The refractive index
On the basis of number of modes:-
on the basis of number of modes of propagation
the optical fiber are classified into two types:
(i) Single mode fiber (SMF) and
(ii) Multi-mode fiber (MMF)
• Single-mode fibers – in single mode fiber only one
mode can propagate through the fiber. This type
of fiber has small core diameter(5um) and high
cladding diameter(70um) and the difference
between the refractive index of core and
cladding is very small. The light is passed through
the single mode fiber through laser diode.
• Multi-mode fiber :-
• Multi mode fiber allows a large number of modes for the
light ray travelling through it.
• The core diameter is (40um) and that of cladding is(70um)
• The relative refractive index difference is also larger than
single mode fiber.
• There is signal degradation due to multimode dispersion.
• They are not suitable for long distance communication
due to large dispersion and attenuation of the signal.
REFRACTION AT A
PLANE SURFACE
Refraction
Refraction is the changing direction of
light when it goes into a material of
different density
ON THE BASIS OF REFRACTIVE INDEX
• There are two types of optical fiber:-
• (i) Step-index optical fiber
• (ii) Graded-index optical fiber
• Step
STEP INDEX FIBER
• The refractive index of core is constant
• The refractive index of cladding is also constant
• The light rays propagate through it in the form of
meridiognal rays which cross the fiber axis during every
reflection at the core cladding boundary.
GRADED INDEX FIBER
• In this type of fiber core has a non uniform refractive index
that gradually decrease from the centre towards the core
cladding interface.
• The cladding has a uniform refractive index.
• The light rays propagate through it in the form of skew rays
or helical rays. They do not cross the fiber axis at any time.
HOW OPTICAL FIBER’S ARE MADE??
• Three Steps are Involved in the manufacturing of
the optical fiber which are given below:-
-Making a Preform Glass Cylinder
-Drawing the Fiber’s from the preform
-Testing the Fibre
OPTICAL FIBER COMMUNICATION
SYSTEM
Electrical
I nformation source Optical Optical fiber Optical Electrical
Destination
source source cable detector receive
• Information source- it provides an electrical signal to
a transmitter comprising an electrical stage.
• Electrical transmitter- It drives an optical source to
give an modulation of the light wave carrier.
• Optical source- It provides the electrical-optical
conversion .It may be a semiconductor laser or an
LED.
• Optical cable: It serves as transmission medium.
• Optical detector: It is responsible for optical to
electrical conversion of data and hence
responsible for demodulation of the optical carrier.
It may be a photodiodes, phototransistor, and
photoconductors.
• Electrical receiver: It is used for electrical interfacing
at the receiver end of the optical link and to
perform the signal processing electrically.
• Destination: It is the final point at which we receive
the information in the form of electrical signal.
ATTENUATION
• Attenuation is the loss of the optical power.
• Attenuation in optical fiber take place due to
elements like coupler, splices, connector and fiber
itself.
• A fiber lower attenuation will allow more power to
reach a receiver than with a higher attenuation.
• Attenuation may be categorised as –
(i) Intrinsic
(ii) Extrinsic
FACTOR CAUSING ATTENUATION IN
FIBER
• Fig. shows the factor affecting the attenuation in
fiber-
Attenuation
Extrinsic
Intrinsic
Macrobending
Absorption Scattering Microbending
VARIATION OF SPECIFIC
ATTENUATION WITH WAVELENGTH
ATTENUATION & WAVELENGTH
• The specific attenuation ( power loss in
dB per unit length ) actually depends
on the wavelength of the radiation
travelling along the optic fibre
• The graph shows minima at 1310nm
and 1550nm, which implies that these
are desirable wavelengths for optimal
transmission
• These are infra red wavelengths
ADVANTAGE OF OPTICAL FIBER
COMMUNICATION
1) The life of fiber is longer than copper wire
2) Handling and installation costs of optical fiber is
very nominal
3) It is unaffected with electromagnetic interference
4) Attenuation in optical fiber is lower than coaxial
cable or twisted pair.
5) There is no necessity of additional equipment for
protecting against grounding and voltage
problems.
6) As it does not radiates energy any antenna or
detector cannot detects it hence provides signal
security
DISADVANTAGE
1) Highly skilled staff would be required for
maintenance
2) Only point to point working is possible on optical
fiber
3) Precise and costly instruments would be
required
4) Costly if under utilized.
5) Accept unipolar codes only.
6) Jointing of fiber and splicing is also time
consuming.
APPLICATIONS
• Optical fiber have wider range of application in
almost all field, some are been specified below
• In telecommunication field
• In space applications
• Broadband applications
• Computer applications industrial
applications
• Mining applications
• In medical applications
• In military applications etc.
• Optical fiber have wider range of application in almost all field, i.e. in medical,
electronics, military etc .some are been specified below
• Medical
• Military
• Electronics
IBM microprocessors
THE ENDOSCOPE
There are two optical fibres
One for light, to illuminate
the inside of the patient
One for a camera to send
the images back to the
doctor.
Key hole surgery
THANK YOU
