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)
3.
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.
5.
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.
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”)
9.
10.
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
13.
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.
19.
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
21.
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
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
27.
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
29.
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
32.
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
34.
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).
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.
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.
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.
46.
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