1. WELCOME
TO SEMINAR
ON

2. MADE BY -
PRATYUSH
EC – 42 (Roll No.-35)
OPTICAL FIBER CABLE

3. CONTENTS
 Brief Introduction
 History
 Optical fiber construction
 Critical angle & Total Internal Reflection
 Types of fibers/transmission modes
 Acceptance angle & acceptance cone
 Numerical Aperture
 V-Number
 Dispersion & its types
 Attenuation and Losses in Fiber
 Fiber optic communication
 Fiber Vs Copper Cable
 Fiber VS Co-axial Cable
 Disadvantages
 Applications
 References

4. BRIEF INTRODUCTION
 Optical fiber is flexible, transparent fiber
made of silica or plastic slightly thicker than a
human hair
 It is a form of guided or wired non conducting
medium
 Its working is based on principle of Total
Internal Reflection
 It permits transmission over longer distances
and at higher bandwidths than other forms of
communication

5. HISTORY
 In 1870, Tyndall introduced concept of Total
Internal Reflection with a demonstration.
 In the same year, Alexander Graham Bell,
developed a optic voice transmission, which he
named the photo phone.

6. HISTORY (contd.)
 Later around 1954, Brien, Hopkins & Kapany
achieved low loss transmission through 75 cm
bundle of thousand fibers
 Jun-ichi Nishizawa, was the first to propose the use
of optical fibers for communications in 1963
 Kao and Hockham were first to reduce attenuation
in optical fibers below 20 (dB/km), making it a
practical communication medium which earned Kao
the Nobel Prize in Physics in 2009.

7. OPTICAL FIBER
CONSTRUCTION
 Core
Glass or plastic with a higher index of
refraction than the cladding
Carries the signal
 Cladding
Glass or plastic with a lower index of
refraction than the core
 Buffer
Protects the fiber from damage and
moisture
 Jacket
Holds one or more fibers in a cable

8. CRITICAL ANGLE & TOTAL
INTERNAL
REFLECTION
 Critical angle is angle of incidence in denser
medium for which angle of refraction in rarer
medium is 90 degrees.
 Total internal reflection-If angle of incidence in
denser medium is increased beyond critical angle
, then ray of light is reflected back completely into
denser medium.

9. OPTICAL FIBER TRANSMISSION
MODES/ TYPES OF FIBERS

10. TYPES OF FIBERS (contd.)
 Multimode step-index fiber
 the reflective walls of fiber move light pulses to
receiver
 Multimode graded-index fiber
 acts to refract light toward center of fiber by
variations in density
 Single mode fiber
 the light is guided down center of an extremely
narrow core

11. TYPES OF FIBERS (contd.)

12. SINGLE MODE FIBER
Advantages:
 Minimum dispersion: all rays take same path,
same time to travel down the cable. A pulse can
be reproduced at the receiver very accurately.
 Less attenuation, can run over longer distance
without repeaters.
 Larger bandwidth and higher information rate
Disadvantages:
 Difficult to couple light in and out of the tiny core
 Highly directive light source (laser) is required
 Interfacing modules are more expensive

13. MULTIMODE FIBER
 Multimode step-index Fibers:
 inexpensive
 easy to couple light into Fiber
 result in higher signal distortion
 lower TX rate
 Multimode graded-index Fiber:
 intermediate between the other two types of
Fibers

14. ACCEPTANCE ANGLE
 Acceptance angle is maximum angle at
which a light ray enters into core and
propagate through it in zigzag path
Acceptance
angle

15. ACCEPTANCE CONE
 If all possible direction of acceptance angle
are considered at same time we get a cone
corresponding to surface known as
acceptance cone

16. NUMERICAL APERTURE
 It defines gathering capability of fiber
mathematically expressed as sine of acceptance
angle
 High Numerical Aperture increases dispersion
hence low Numerical Aperture is desirable

17. V- NUMBER
 No. of modes supported by optical fiber is
obtained by cut-off condition known as
normalized frequency or V-Number
 Number of modes (N) = ½ V²
 V- number can be reduced either by reducing
numerical aperture or by reducing diameter of
fiber

18. DISPERSION & ITS TYPES
 Dispersion is the spreading out of a light
pulse as it travels through the fiber
 It is of two main types:
 Intermodal or Modal Dispersion
 Intra modal or Chromatic Dispersion

19. INTERMODAL OR
MODAL
DISPERSION
 Spreading of a pulse because different modes
(paths) through the fiber take different times
 Only happens in multimode fiber
 Reduced, but not eliminated, with graded-index fiber

20. INTRA MODAL OR CHROMATIC
DISPESRSION
 Different wavelengths travel at different
speeds through the fiber
 This spreads a pulse in an effect named
chromatic dispersion
 Chromatic dispersion occurs in both single
mode and multimode fiber
 It is of two types
1) Material Dispersion which is wavelength
based effect caused by glass of which fiber is
made
2) Waveguide Dispersion occurs due to
change in speed of wave propagating through
waveguide

21. ATTENUATION
 Modern fiber material is very pure, but there is still
some attenuation
 The wavelengths used are chosen to avoid absorption
bands
-850 nm, 1300 nm, and 1550 nm
-Plastic fiber uses 660 nm LEDs

22. LOSSES IN FIBER
 Absorption Losses- due to material,
impurities & atomic defects in glass fiber
 Geometric Effects- due to manufacturing
defects like irregular diameter of core
 Rayleigh Scattering-
 Change in local refractive index due to local
microscopic variation density
 It is a scattering loss

23. FIBER OPTIC
COMMUNICATION
Input
Signal
Coder or
Converter
Light
Source
Source-to-Fiber
Interface
Fiber-to-light
Interface
Light
Detector
Amplifier/Shaper
Decoder
Output
Fiber-optic Cable
Receiver
TX, RX, and Fiber Link
Transmitter

24. FIBER OPTIC
COMMUNICATION
(contd.)
 Light source:
 Amount of light emitted is proportional to the drive current
 Two common types:
 LED (Light Emitting Diode)
 ILD (Injection Laser Diode)
 Source–to-fiber-coupler (similar to a lens):
 A mechanical interface to couple the light emitted by the
source into the optical fiber
 Light detector:
 PIN (p-type-intrinsic-n-type)
 APD (avalanche photo diode)
 Both convert light energy into current.
Note- For long links,repeaters are used to compensate for

25. FIBER VS COPPER CABLE
 Smaller size & weight
 Greater capacity
 Faster communication
 Transmit over Longer distances
 Can be used for both analog & digital
transmission
 Broader Bandwidth – more data per second

26. FIBER VS COPPER CABLE
(CONTD.)
 Immunity to Electromagnetic Interference
 Low attenuation/transmission loss over long
distances
 Electrical Insulator
 Lack of costly metal conductor
 Dielectric waveguide
 Signal Security

27. FIBER VS CO-AXIAL
CABLE
 More information carrying capacity with higher data
rates and fidelity
 Greater transmission speed
 Smaller in size and light in weight
 Easier to handle and install
 Immune towards environmental hazards &
electromagnetic interference
 Higher Bandwidth
 Economical
 Low signal loss

28. DISADVANTAGES
 Cumulative losses due to large size of fiber
couplers
 Hazardous emissions like glass shards &
optical radiation
 Requires technicians with special expertise for
installation & maintenance

29. APPLICATIONS
 Used in Cable T.V. , HDTV, LANs & CCTV
systems
 Used in Optic Fiber Communication for
transmission of analog & digital data
 Used in Imaging Optics & Spectroscopy
 Used in illumination applications
 Used in various military applications
 Fiber optic sensors & couplers

30. REFERENCES
 Govind P. Agrawal, “Fiber Optic Communication
Systems”, John Wiley, 3rd Edition,2004.
 R J Hoss and EA Lacy, Fiber optics 2nd edition
(Prentice Hall, New Jersey, 1993)
 John M. Senior, “Optical Fiber Communications”,
PEARSON, 3rd Edition, 2010.
 Gerd Keiser, “Optical Fiber Communications”,
TMH, 4th Edition, 2008.
 Joseph C. Plais, “Fiber Optic Communication”,
Pearson Education, 4th Ed, 2004.

31. THANK
YOU