The document provides a comprehensive overview of optical fibers, detailing their structure, advantages, and working principles, including total internal reflection and numerical aperture. It describes various types of optical fibers such as single-mode and multi-mode step-index fibers, and emphasizes their applications in medical and mechanical imaging. The content is developed by students under the guidance of a professor at Vadodara Institute of Engineering.

1. Subject: Engineering Physics.
Mechanical F.Y. (shift 2)
Vadodara Institute of Engineering.
Kotambi

2. Credits:
Vadodara Institute of Engineering.
 Kothari Vrajesh 130800119517
 Ojha Anandvardhan 130800119518
 Pandya Kaushal 130800119519
 Pandya Param 130800119520
Under the guidance of:
Professor Anand M Panchal.

3. Vadodara Institute of Engineering.
Topic:

4. Contents :
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 Introduction..
 Advantages..
 Total Internal Reflection..
 Numerical Aperture..
 Acceptance Angle..
 Types of Fibre..

5. Introduction
 An optical fiber is essentially a waveguide for light.
 It consists of a core and cladding that surrounds the core.
 The index of refraction of the cladding is less than that of
the core, causing rays of light leaving the core to be
refracted back into the core.
 A light-emitting diode (LED) or laser diode (LD) can be
used for the source.
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6. What’s inside a fiber cable ?
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7. Layers surrounding Fiber cables
 Primary coating
 Gives additional mechanical strength
 Protects fiber from stress
 Protection against chemical attacks
 Buffer jacket
 Avoids the formation of microbends
 Bending stress is relieved
 Fiber losses are reduced
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8. Layers surrounding Fiber cables…
 Outer Jacket
 To reduce abrasion and to provide extra protection
against external mechanical strength
 Filler materials
 To avoid moisture absorption by fibers
 Prevents corrosion
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9. Layers of Fiber cables
Core
8µm
Cladding
125µm
Buffer
250 µm
Jacket
400 µm
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10. Advantages of Optical fibre 
 Less expensive.
 Thinner.
 Higher carrying capacity.
 Less signal degradation Light signals Low power .
Digital signals Non-flammable .
 Lightweight .
 Flexible Medical imaging.
 Mechanical imaging - inspecting mechanical welds in pipes and
engines (in airplanes, rockets, space shuttles, cars)
 Plumbing - to inspect sewer lines
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11. The Basic principle :
Total Internal Reflection.
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 At some angle, known as the critical angle θc, light
traveling from a higher refractive index medium to a lower
refractive index medium will be refracted at 90° i.e.
refracted along the interface.
 If the light hits the interface at any angle larger than this
critical angle, it will not pass through to the second medium
at all. Instead, all of it will be reflected back into the first
medium, a process known as total internal reflection

12. Vadodara Institute of Engineering.
 The angle of refraction at the interface between
two media is governed by Snell’s law:
2211 sinsin  nn 

13. Numerical Aperture
 The numerical aperture of the
fiber is closely related to the
critical angle and is often used in
the specification for optical fiber
and the components that work
with it
 The numerical aperture is given
by the formula:
 The angle of acceptance is
twice that given by the numerical
aperture.
2
2
2
1.. nnAN 
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14. Acceptance Angle..
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 Acceptance angle of the fibre Φmax is defined as the
maximum value of the angle of incidence at the
entrance 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:
sin Φmax = (n1
2 – n2
2 )0.5

15. Vadodara Institute of Engineering.

16. Types of Optical Fiber.
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17. Single mode Step-Index Fibre (SMSI Fibre)
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 A single mode step index fibre has a central core
material of uniform refractive index value.
 The diameter of the core is (8 – 10 µm) sufficiently
small so that, there is essentially only one path that
light may take as it propagates down the cable.

18. Multi mode Step-Index Fibre.
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 In comparison to the single-mode fibre, multimode
fibre has a relatively large core of diameter 50 – 25
µm and a high numerical aperture.
 The diameter of the cladding usually lie between
100-250µm.

19. Multimode Graded Index Fibre.
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 In an effort to reduce the pulse dispersion,
multimode graded index fibre was developed.
 A graded index index fibre is characterized by a
central core that has a refractive index which is not
uniform.

20. Vadodara Institute of Engineering.

21. Reference :
Vadodara Institute of Engineering.
 Engineering Physics by G. Vijayakumari.
 Engineering Physics by V Rajendran.
 http://en.wikipedia.org/wiki/Optical_fiber

22. Vadodara Institute of Engineering.