Optical fibers transmit light through thin glass or plastic strands. They work using the principle of total internal reflection. Light traveling through the fiber's core at an angle greater than the critical angle will reflect off the cladding instead of passing through. This allows fibers to carry signals over long distances with minimal loss. Optical fibers have advantages over metal cables like greater bandwidth, lighter weight, immunity to electromagnetic interference, and ability to carry more data. Their main uses are in telecommunications, local area networks, cable TV, and medical endoscopy.

1. Fiber Optics
(Optical Fiber Communication)

2. What is an Optical Fiber?
▶ An optical fiber is a wave guide through which EM waves of optical
frequencies can be made to travel through it for long distances.
▶ But, what is a wave guide?
▶ A waveguide is a structure that guides waves, such as electromagnetic
waves or sound,or light with minimal loss of energy by restricting the
transmission of energy to one direction.
▶ (Ex: A coaxial copper cable)

4. Optical Fibers are hair-
thin, transparent strands
through which light can be
transmitted.
A group of many such
optical fibers constitute a
Optical Fiber Cable.

6. Advantages of Optical Fibers:
▶ 1.High Speed of communication(signals are transmitted at speed of light).
▶ 2.Minimum attenuation of signals(minimum losses).
▶ 3.Large Bandwidth of signals(More signals can be transmitted).
▶ 4.Low cost per cable length.
▶ 5.Can sustain adverse atmospheric conditions.

7. Snell’s Law

8. Principle of operation:
▶ It works on the principle of TIR(Total Internal Reflection).
▶ Total internal reflection(TIR) is an optical phenomenon that happens when a ray
of light strikes a medium boundary at an angle larger than a particular critical
angle with respect to the normal to the surface. (in simple terms: “when the
angle of incidence is greater that the critical angle, then the light ray is totally
reflected back into the original medium-this is TIR”)

11. Optical Fiber Construction:
An optical fiber consists of a central cylinder called CORE.
The CORE is surrounded by another cylinder called CLADDING.
Both CORE & CLADDING are encapsulated in a protective COATING called BUFFER JACKET.
The Refractive Index of CORE is always greater than CLADDING.

12. Conditions for the TIR to occur and the
light to propagate through the fiber
1. The refractive index of the core (n1)
should be greater than that of
cladding (n2)
2. At the core-cladding interface, the
angle of incidence must be greater
than the critical angle θC

14. Optical Fiber Classification:
▶ Optical Fibers are classified into 3 categories:
Optical Fibers
Based on type of
material
Based on Mode of
propagation
Based on Refractive
Index

15. Optical Fibers
Based on type of
material
Based on Mode of
propagation
Based on Refractive
Index
1.All Glass Fibers
• 2.All Plastic Fibers
3.Glass Core Plastic clad Fibers
• 4.PCS(Polymer clad silica ) Fibers
1.Single Mode Fiber
2.Multi Mode Fiber
1.Step-Index Fiber
2.Graded Index Fiber

16. Single Mode Fibers
▶ Single Mode cable is a glass fiber with a relatively narrow diameter of 8.3 to 10 microns that
has only one mode of transmission (Only one path for the light propagation), used to transmit one
signal per fiber (in telephone and cable TV)
▶ Single Mode Fiber gives higher transmission rate and up to 50 times more distance than multimode.
▶ It Carries higher bandwidth than multimode fiber, but requires a light source with a narrow width.
▶ Single-mode fiber has a much smaller core than multimode.

17. 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

18. Multi-Mode Fiber
▶ Multi-Mode Fiber has more than one path (mode) for the propagation of light with a
larger diameter in the range 50-100 micron for the light to propagate.
▶ Multimode fiber gives a high bandwidth at high speeds over medium distances.
▶ Light waves are dispersed into numerous paths, or modes and hence leads to signal
distortion resulting in incomplete data transmission.
▶ Typical multimode fiber core diameters are 50, 62.5, and 100 micrometers.

20. Step-index & Graded Index fibers
A step-index fiber is one which has a uniform refractive index within the core and a sharp
decrease ( a s t e p c h a n g e ) in refractive index at the core-cladding interface so that
the cladding is of a lower refractive index.
A gradient-index fiber is an optical fiber whose core has a refractive index that
decreases with increasing radial distance from the optical axis of the fiber in a parabolic manner.
Multi mode graded index fiber

22. I. Singlemode Step-Index Fiber (SMSI Fiber)
Single-mode step-index Fiber
n1 core
n2 cladding
no air
Light
ray
Index of
refraction
22

23. II. Multimode Step-Index Fiber
Multimode step-index Fiber
n1 core
n2 cladding
no air
Index of
refraction
23

24. III. Multimode Graded Index Fiber
Variable
n
Index profile
Multimode graded-index Fiber
Index of
refraction
24

25. Multimode Fibers

26. 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

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

30. 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

31. 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

33. 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

35. Numerical Aperture & Acceptance angle
▶ The Numerical Aperture (NA) is a maximum light gathering capacity of an optical fiber.
▶
▶ Where, n1 is the refractive index of core ,
▶ n2 is the refractive index of cladding.
▶ Acceptance angle (θ): It is the maximum angle made by the light ray with the fiber axis, so that
light can propagate through the fiber after total internal reflection.
▶ θ = sin-1(NA)

36. Attenuation
▶ Attenuation is the loss of optical power as light travels along the fiber.
▶ Attenuation in an optical fiber is caused by absorption, scattering, and bending
losses.
Signal attenuation is defined as the ratio of optical input power (Pi) to the optical output
power (Po).
Optical input power is the power injected into the fiber from an optical
source. Optical output power is the power received at the fiber end or
optical detector. The following equation defines signal attenuation as a
unit of length:
Length (L) is expressed in kilometers.
Therefore, the unit of attenuation is decibels/kilometer (dB/km).

37. Attenuation
Absorption Scattering Bending

38. ABSORPTION
▶ Absorption is defined as the portion of attenuation resulting from the
conversion of optical power into another energy form, such as heat.
▶ Absorption in optical fibers is explained by three factors:
▶ Imperfections in the atomic structure of the fiber material
▶ The intrinsic or basic fiber-material properties
▶ The extrinsic (presence of impurities) fiber-material properties

39. Scattering & Bending losses
▶ SCATTERING. - Basically, scattering losses are caused by the interaction of light with
density fluctuations within a fiber.
▶ During manufacturing, regions of higher and lower molecular density areas, relative
to the average density of the fiber, are created. Light traveling through the fiber
interacts with the density areas, Light is then partially scattered in all directions.
▶ BENDING LOSSES. - Bending the fiber also causes attenuation. Bending loss is
classified according to the bend radius of curvature.

41. MICRO BENDING LOSSES

42. •Micro-bend Losses are caused by small
discontinuities or imperfections in the fiber.
•Micro bending is a loss due to small bending or
distortions. This small micro bending is not
visible.
•The losses due to this are temperature related,
tensile related or crush related.
•Uneven coating applications and improper
cabling procedure increases micro bend loss.
External forces are also a source of micro
bends.

43. T
ransmitter
▶
▶
Encoder Driver
Circuit
Light
Source
Photo
Detector
Amplifier
Signal
Restorer Decoder
Receiver
Transmitter
Analog signal
Analog signal
i/p
o/p
OF
OF
Optical Fiber Communication System

44. Working:
▶ Encoder: It is an electronic system that conerts analog information (voice/data/objects
etc.) into binary data. The binary data may be a series of electrical pulses.
▶ Transmitter
▶ It consists of two parts:
▶ 1.Driver ckt:It supplies electrical signals to the light source from the encoder in the
required sequential form.
▶ 2.Light source:It is an LED or a LASER diode which converts electrical signals to optical
signals.
▶ O/P from the light source is sent to an Optical Fiber.

45. ▶ Receiver: It consists of 3 parts:
▶ 1.Photo detector:It converts optical signals into equivalent electrical signals and
supplies them to amplifier.
▶ 2.Amplifier:It amplifies the signals and sends them to signal restorer.
▶ 3.Signal Restorer:It keeps all signals in sequential form and supplies them to decoder
in a suitable way.
▶ Decoder: It converts the received signals into analog information form.

47.  In Telecommunications totransfer data
 In Local Area Networks to share internet connections.
 In Cable TV and CCTV.
 In Optical Fiber Sensors.
 In Endoscopy to view internal body organs.
 In decoration

48. 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

49. 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

50. 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

51. 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

52. 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