FIBER OPTIC COMMUNICATION

1. UNIT V OPTICAL FIBER COMMUNICATION
 SUDHEESH.S


2. 7.2
Figure 7.1 Transmission medium and physical layer

3. 7.3
Figure 7.2 Classes of transmission media

4. 7.4
Figure 7.3 Twisted-pair cable

5. 7.5
Figure 7.7 Coaxial cable

6. Fiber-optic Cable
Many extremely thin strands of glass or plastic bound
together in a sheathing which transmits signals with light
beams
Can be used for voice, data, and video

7. Introduction to Optical Fibers.
 Fibers of glass
 Usually 120 micrometers in diameter
 Used to carry signals in the form of light over distances up to
50 km.
 No repeaters needed.

8. Fiber v. Copper
 Optical fiber transmits light pulses
 Can be used for analog or digital transmission
 Voice, computer data, video, etc.
 Copper wires (or other metals) can carry the same types of
signals with electrical pulses

9. Optical Fiber & Communications System

10. FREQUENCIES
 Frequency refers to the modulating message signal
Frequency.
 The rapid exchange of energy from the beam to the dot
excites the phosphor into the radiating photon of energy
which agitate at 4.2857×10^64 times/sec.

11.  Fiber Optics are cables that are made of optical fibers that
can transmit large amounts of information at the speed of
light.

12. Glass Fibers

13. Characteristics
 Glass Core
 Glass Cladding
 Ultra Pure UltraTransparent Glass
 Made Of Silicon Dioxide
 LowAttenuation
 Popular among industries

14. Plastic Fibers

15. Optical Fiber
 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

16. Total Internal Reflection
 Optical fibers work on the principle of total internal
reflection
 With light, the refractive index is listed
 The angle of refraction at the interface between two
media is governed by Snell’s law:
n1 sin1  n2 sin2

17. Reflection

18. Refraction
When a ray of light crosses from
one material to another, the amount
it bends depends on the difference
in index of refraction between the
two materials

19. 17.1 Index of refraction
 The ability of a material to bend rays of light is described by the
index of refraction (n).

20. Refraction & Total Internal Reflection

21. Total Internal Reflection
 Optical fibers work on the principle of total internal
reflection
 The angle of refraction at the interface between two
media is governed by Snell’s law:
n1 sin1  n2 sin2

22. 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 

23. 7.23
Figure 7.12 Propagation modes
Figure 7.13 Modes
1. Single-mode fiber
Carries light pulses
along single path.
2. Multimode fiber
Many pulses of light
travel at different
angles

24. Multi-Mode vs. Single-mode

25. Singlemode Fiber
 Singlemode fiber has a core diameter of 8 to 9 microns, which
only allows one light path or mode
 Images from arcelect.com (Link Ch 2a)
Index of
refraction

26. Singlemode FIber
 Best for high speeds and long distances
 Used by telephone companies and CATV

27. Multimode Step-Index Fiber
 Multimode fiber has a core diameter of 50 or 62.5 microns
(sometimes even larger)
 Allows several light paths or modes
 This causes modal dispersion – some modes take longer to pass
through the fiber than others because they travel a longer distance
 See animation at link Ch 2f
Index of

28. Step-index Multimode
 Large core size, so source power can be efficiently coupled to
the fiber
 High attenuation (4-6 dB / km)
 Low bandwidth (50 MHz-km)
 Used in short, low-speed datalinks
 Also useful in high-radiation environments, because it can be
made with pure silica core

29. Multimode Graded-Index Fiber
 The index of refraction gradually changes across the core
 Modes that travel further also move faster
 This reduces modal dispersion so the bandwidth is greatly increased
Index of

30. Graded-index Multimode
 Useful for “premises networks” like LANs, security systems,
etc.
 62.5/125 micron has been most widely used
 Works well with LEDs, but cannot be used for Gigabit Ethernet
 50/125 micron fiber andVSELS are used for faster networks

31. 7.31
Table 7.3 Fiber types
In multimode step-index fiber, the density of the core remains constant from the
center to the edges. A beam of light moves through this constant density in a straight
line until it reaches the interface of the core and the cladding. At the interface, there is
an abrupt change due to a lower density; this alters the angle of the beam's motion. The
term step index refers to the suddenness of this change, which contributes to the
distortion of the signal as it passes through the fiber.
In multimode graded-index fiber, decreases this distortion of the signal through the
cable. The word index here refers to the index of refraction. As we saw above, the index
of refraction is related to density. A graded-index fiber, therefore, is one with varying
densities. Density is highest at the center of the core and decreases gradually to its
lowest at the edge. Figure 7.13 shows the impact of this variable density on the
propagation of light beams.

32. Optical Fiber Cable Construction

33. How are Optical Fibre’s made??
 Three Steps are Involved
-Making a Preform Glass Cylinder
-Drawing the Fibre’s from the preform
-Testing the Fibre

34. Modified Chemical Vapor
Deposition (MCVD)

35. Fiber and Acrylate Coating
 Optical fiber is covered by an acrylate
coating during manufacture
 Coating protects the fiber from moisture and
mechanical damage

37. Advantages of Optical Fibre
 Thinner
 Less Expensive
 Higher Carrying Capacity
 Less Signal Degradation& Digital Signals
 Light Signals
 Non-Flammable
 LightWeight

38. Areas of Application
 Telecommunications
 LocalArea Networks
 CableTV
 CCTV
 Optical Fiber Sensors

39. Type of Fibers
Optical fibers come in two types:
 Single-mode fibers – used to transmit one signal per fiber
(used in telephone and cableTV).They have small cores(9
microns in diameter) and transmit infra-red light from laser.
 Multi-mode fibers – used to transmit many signals per fiber
(used in computer networks).They have larger cores(62.5
microns in diameter) and transmit infra-red light from LED.

40. Splices and Connectors
 In fiber-optic systems, the losses from splices and connections can be
more than in the cable itself
 Losses result from:
 Axial or angular misalignment
 Air gaps between the fibers
 Rough surfaces at the ends of the fibers

41. How are Optical Fibre’s made??
 Three Steps are Involved
-Making a Preform Glass Cylinder
-Drawing the Fibre’s from the preform
-Testing the Fibre

42. Testing of Optical Fiber
 Tensile Strength
 Refractive Index Profile
 Fiber Geometry
 Information Carrying Capacity
 Operating temperature/humidity range
 Ability to conduct light under water
 Attenuation

43. Optical Fiber Laying
 Mechanical Linking
 Includes coupling of two connectors end to end
 Optical distribution frames allow cross connect fibers from by means of
connection leads and optical connectors
 Soldering:
 This operation is done with automatic soldering machine that ensures:
 Alignment of fiber’s core along the 3 axis
 Visual display in real-time of the fibers soldering
 Traction test after soldering (50 g to 500 g)

44. Optical Fiber Laying (Cont…)
 Blowing
 Used in laying optical cables in roadways.
 Cables can be blown in a tube high density Poly Ethylene
 Optical fiber is then blown in the tube using an air compressor
which can propel it up to 2 kilometers away.

45. Tools of Trade
 Cleaning fluid and rags
 Buffer tube cutter
 Reagent-grade isopropyl alcohol
 Canned air
 Tape (masking or scotch)
 Coating strip
 Microscope or cleaver checker
 Splicer
 Connector supplies

46. Fiber Optics Test Kit
 Features
 Includes Smart FO Power Meter and Mini LED or laser source
 FO test lite software for data logging
 Tests all networks and cable plants
 New versions of Gigabit Ethernet
 Low Cost
 Applications
 Measure optical power or loss
 Trouble shooting networks

47. Protecting Fibers
 Tougher than copper wires
 Designed in three concentric layers
 Core – Cladding – Buffer
 Two basic buffer types
 Tight buffer
 Loose tubes

48. Implementation of Different LANs
 IEEE 802.3
 FOIRL
 Fiber optic inter repeater link
 Defines remote repeaters using fiber optics
 Maximum length – 1000 meters between any two repeaters.

49. IEEE 802.3 (Cont…)
 10BASEF
 Star topology with hub in the center
 Passive hub:
 Short cables
 No cascading
 Reliable
 Active hum:
 Synchronous
 May be cascaded
 Do not count as one repeater
 Any 10BASEF active hub must have at least two FOIRL ports

50. Token Ring
 Advantages
 Long range
 Immunity to EMI/RFI
 Reliability
 Security
 Suitability to outdoor applications
 Small size
 Compatible with future bandwidth requirements and future
LAN standards

51. Token Ring (Cont…)
 Disadvantages
 Relatively expensive cable cost and installation cost
 Requires specialist knowledge and test equipment
 No IEEE 802.5 standard published yet
 Relatively small installed base.

52. Fiber Distributed Data Interface
 Stations are connected in a dual ring
 Transmission rate is 100 mbps
 Total ring length up to 100s of kms.

53. Conclusion
This concludes our study of Fiber Optics. We have
looked at how they work and how they are made. We have
examined the properties of fibers, and how fibers are
joined together. Although this presentation does not
cover all the aspects of optical fiber work it will have
equipped you knowledge and skills essential to the fiber
optic industry.