1. DEP5313-FIBER OPTIC COMMUNICATION SYSTEM
TOPIC 1: FIBER OPTIC CHARACTERISTICS

2. COURSE LEARNING OUTCOME
Apply the concepts of light properties in the fiber optic communication system. (C3, PLO1)
Solve problems regarding light transmission in fiber optic communication link. (C3, PLO2)
Design fiber optic communication link using link budget. (C5, PLO4)
Display the ability to handle systematically the testing instruments for fiber optic communication system. (P4, PLO5)

3. Fiber optics
A means to carry information from one point to another or serves as transmission medium (optical fiber).
A technology that uses thin strand of glass (or plastic) threads (fibers) to transmit data.
A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves.

4. Bandwidth of Light Wave
Light is a kind of electromagnetic radiation, hence it is part of the electromagnetic spectrum represent electromagnetic radiation of different wavelengths.
104
105
106
107
108
109
1010
1011
1012
1013
1014
1015
1016
103
102 10 1
10-1
10-2
10-3
10-4
10-5
10-6
10-7
VLF LF MF HF
VHF
UHF
SHF
EHF IR UV VR
Telephone
Lines
AM Radio
Broadcast TV
Satellite
Downlink
Fiber Optic
Wavelengths
Visible
Light
Fiber optic transmission wavelengths
Electromagnetic Frequency Spectrum

5. Bandwidth of Light Wave
Light frequency spectrum can be divided into three general bands:
1. Ultravoilet
Known as “beyond voilet”
Invisible to human eye
Causes sunburns
2. Visible
Light wavelength which human eye will respond
3. Infrared
human eye
harmless to the body.

6. Bandwidth of Light Wave
Ultraviolet
Band of light wavelengths that are too short to be seen by the human eye.
Visible
Band of light wavelengths to which the human eye will respond.
Infrared
Band of light wavelengths that are too long to be seen by the human eye.

7. Fiber Optic Spectrum Frequency
Transmission Windows: where optical attenuation is low
Band
Description
Wavelength Range
O band
original
1260 to 1360 nm
E band
extended
1360 to 1460 nm
S band
short wavelengths
1460 to 1530 nm
C band
conventional ("erbium window")
1530 to 1565 nm
L band
long wavelengths
1565 to 1625 nm
U band
Ultra long wavelengths
1625 to 1675 nm

8. Propagation of Light Velocities
Light travels with speed of light :
c = 3 x 108 m/s.
Thus , wavelength of light
λ = c/f
λ is the wavelength of the light in meters
f is the frequency of the light in hertz (Hz)
c is the speed of light

9. The characteristics of light (properties)
The light characteristic is useful in an optical link :
Light travel in a straight line
According to Planck, each quantum of a light contains energy proportional to the frequency f of the light as given by:
E = hf , Where h is called the Planck constant which has a value of x10-34 Joules.
Power(Watts, dBm) , Wavelength (m), frequency (Hz)
Light travels in vacuum or air with a speed of is 3x108 m/s
Light travels in materials with slower speed then 3x108 m/s

10. The characteristics of light (properties)
Charge less - does not interact with other light, can go through each other.
Can be visible or invisible.
Light can be refracted if its travel through two different medium. Refraction is the deflection of light.
A visible light ray is reflected from a mirror or a highly polished plane metal surface such as the reflecting surface of an aluminum foil.
Light can be polarized using polarization (angle: degree)

11. Refraction
Occurs when the light travel between 2 media with different density - The light waves spread out along its beam.
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.

12. Refraction DEFINITION :
The index of refraction , n, of a material is the ratio of the speed of light (c) in a vacuum to the speed of light in the material (v).
SNELL’S LAW OF REFRACTION
When light travels from a material with one index of refraction to a material with a different index of refraction, the angle of incidence is related to the angle of refraction by

13. Index of Refraction SUBSTANCE INDEX OF REFRACTION, n Solids at 20 °C
Diamond
2.419
Glass, crown
1.523
Ice (0°C)
1.300
Sodium chloride
1.544
Quartz
Crystalline
Fused
1.458
Liquids at 20 °C
Benzene
1.501
Carbon disulfide
1.632
Carbon tetrachloride
1.461
Ethyl alcohol
1.362
Water
1.333
Gases at 20 °C
Air
Carbon dioxide
Oxygen, O2
Hydrogen, H2

14. Refraction

15. Refraction CRITICAL ANGLE
The critical angle is measured from the cylindrical axis of the core.
An angle of incidence for which the angle of refraction will be 90°; this is called the critical angle:
For reflection to occur, angle of incidence must exceed the critical angle -Ѳc. The critical angle Ѳ2 may be found by:
n2 – index of refraction medium 1
n1 – index of refraction medium 2

16. Example of critical angle condition
Refraction
Example of critical angle condition

17. Reflection
Reflection is the change in direction of a signal at an interface between two different media so that the signal returns into the medium from which it originated.
The angle of incidence (from the incidence ray to the normal) is equivalent to the angle of reflection (from the reflective ray to the normal).

18. Total Internal Reflection
When a light ray travelling in one material hits a surface of a different material and reflects back into the original material without any loss of light, total internal reflection is said to occur.
This total internal reflection occurs when the angle of incidence greater than the critical angle
Light propagation in fiber optic

19. Total Internal Reflection
Since the core and cladding are constructed from different compositions of glass(different indices), theoretically, light entering the core is confined to the boundaries of the core because it reflects back whenever it hits the cladding, as shown by the following figure.

20. Numerical Aperture (NA)
Is a measurement of the ability of an optical fiber to capture light.
It describes the cone of light accepted into the fiberor exiting the fiber.
Numerical Aperture is the sine ofthe half-acceptance angle
𝑵𝒖𝒎𝒆𝒓𝒊𝒄𝒂𝒍 𝑨𝒄𝒄𝒆𝒑𝒕𝒂𝒏𝒄𝒆 𝑵𝑨= 𝒔𝒊𝒏 𝜽 𝒂

21. The light-gathering ability of an optical fiber, as determined by the square root of the difference of the squares of the refractive indexes of the core (n1) and the cladding (n2).
A light source naturally injects some light rays into the core at angles less than the critical angle, which is perpendicular to the plane of the core/cladding interface.
The numerical aperture essentially is an indication of how well an optical fiber accepts and propagates light.

22. Acceptance Angle
The maximum angle within which light will be accepted by an element, such as a detector or waveguide.
In the latter, it is quantified as half the Vertex Angle of the cone within which Optical Power may be coupled into bound Modes of a fiber. Also called acceptance cone.

23. Related Formula Index of Refraction, Snell’s Law, Critical Angle,
Acceptance Angle,
Numerical Aperture,

24. RECAP
Problem - 1
Given the index of reflection of diamond is and the velocity of light in a vacuum is 2.99 x 108 m/s. Calculate the velocity of light in the material?
Problem - 2
Given the velocity of light in water is x 108 m/s, and the velocity of light in a vacuum is 2.99 x 108 m/s. Calculate the index of refraction of the material?
Problem - 3
Given the index of reflection of diamond is 2.419, benzene 1.501, crystalline is and the velocity of light in a vacuum is 2.99 x 108 m/s. Calculate the velocity of light in all three material?

25. RECAP nair = 1 ncore = 1.46 ncladding = 1.43 qincident = 12°
Problem – 4
Calculate angle of refraction at the air/core interface, r critical angle , c incident angle at the core/cladding interface , i .Will this light ray propagate down the fiber?
nair = 1
ncore = 1.46
ncladding = 1.43
qincident = 12°

26. RECAP
Problem – 5
The searchlight on a yacht is being used to illuminate a sunken chest. At what angle of incidence should the light be aimed?

27. RECAP
Problem – 6 A step index fiber has a core diameter of 100μm and a refractive index of The cladding has a refractive index of Calculate the numerical aperture of the fiber and acceptance angle from air.
Solution:
The numerical aperture is
NA = (n12 – n22)1/ = ( ) 1/2 =

28. TIR not occurred 0i<0c
RECAP
Problem – 7
A beam of light is propagating through diamond and strikes the diamond-air interface at an angle of incidence of 28 degrees. (a) Will part of the beam enter the air or will there be total internal reflection? (b) Repeat part (a) assuming that the diamond is surrounded by water.
(a)
(b)
TIR occurred 0i<0c
TIR not occurred 0i<0c

29. Tutorial
Given an index of reflection of glass is and an index of reflection of air is Determine the acceptance angle if the light is moving from air towards glass.

30. Light Propagation in a Fiber Optic Cable : Propagation modes
Types of FO
MULTI MODE
Step index
Graded index
SINGLE MODE

31. Cable Size
SMF 9
125 micron
MMF
50/125
62.5/125 micron

32. Light Propagation in a Fiber Optic Cable : Single Mode
So narrow that light can travel through it only in a single path.
All the light to travel in only one mode
Is a single stand of glass fiber with a core of 8 to 10 microns in diameter.
Used for long distance more than 5 kilometers in length. (50 times more distance than multimode )
higher transmission rate
provides much better performance with lower attenuation.
is extremely expensive and very difficult to work with.

33. Single Light Propagation
Cladding
Core
Light propogation

34. Light Propagation in a Fiber Optic Cable : Multimode
Has a relatively large light carrying core, usually 62.5 microns or larger in diameter.
Used for short distance transmissions up to maximum length of 5 kilometers.
Light can travel many different paths
Multi-path configuration allows for the possibility of signal distortion at the receiving end
Two types of multimode fiber exist, distinguished by the index profile of their cores and how light travels in them.

35. Multimode step-index
Kevlar B D C
Core
Light Source A
Cladding

36. Light Propagation in a Fiber Optic Cable : Index Profiles: Step Index
Step-index profile
is a refractive index profile characterized by a uniform refractive index within the core and
a sharp decrease in refractive index at the core-cladding interface so that the cladding is of a lower refractive index.
is used in most multimode fibers.

37. Multimode graded-index
Cladding
Core
Light Propogation

38. Light Propagation in a Fiber Optic Cable : Index Profiles :Graded Index
A graded-index or gradient-index Profile
Is a refractive index profile characterized by core having refractive index that decreases with increasing radial distance from the fiber axis.
Because parts of the core closer to the fiber axis have a higher refractive index than the parts near the cladding, light rays follow sinusoidal paths down the fiber.
the refractive index of the core is lower toward the outside of the fiber.
It bends the rays inward and also allows them to travel faster in the lower index of refraction region.

39. Light Propagation in a Fiber Optic Cable : Index Profiles

40. Light Propagation in a Fiber Optic Cable : Index Profiles

41. Summary

42. The Structure of Fiber Cables

43. The Structure of Fiber Cables
CORE
This is the physical medium that transports optical data signals
The core is a single continuous strand of glass or plastic that's measured (size) in micron according to its diameter.
The larger the core, the more light the cable can carry.
The three sizes most commonly available are 50-, 62.5-, and 1 00-micron Gable.
CLADDING
This is a thin layer that surrounds the fiber core
Cladding protects glass from
surface scratches, surface contaminants..
Serves as a boundary to the light waves and causes the refraction to occur , thus enabling data to travel throughout the length of the fiber segment.

44. The Structure of Fiber Cables
COATING
This is a layer of plastic that surrounds the core and cladding to reinforce the fiber core, help absorb shocks, and provide extra protection against excessive cable bends. These buffer coatings are measured in microns (p) and can range from 250 p to 900 p.
STRENGTHENING FIBERS
These components help protect the core against crushing forces and excessive tension during installation. The materials can range from Kevlar to wire strands to gel-filled sleeves.
CABLE JACKET
This is the outer layer of any cable. Most fiber optic cables have an orange jacket, although some may be black or yellow

45. Fiber Types-material Plastic core and cladding
Glass core with plastic cladding
Also called PCS fiber (plastic-clad silica)
Glass core and glass cladding
Also called SCS fiber (silica-clad silica)
Under development:
Non-silicate (Zinc chloride) which could be 1000 times as efficient as glass
Plastic fibers  more flexible and more rugged than glass easier to install, better stress withstanding, less expensive. Less weight 60%
However higher attenuation in plastic. PCS slightly better than SCS for attenuation and radiation

46. Fiber Sizes and Types
Fiber comes in two types, singlemode and multimode. Except for fibers used in specialty applications, singlemode fiber can be considered as one size and type. If you deal with long haul telecom or submarine cables, you may have to work with specialty singlemode fibers. (HSC/PSC- plastic or hard clad silica, plastic cladding on a glass core)

47. Fiber Types and Typical Specifications POF (plastic optical fiber)
 Core/Cladding
 Attenuation
Bandwidth
 Applications/Notes
 Multimode
@850/1300 nm
 50/125 microns
Graded index
  3/1 dB/km
500/500 MHz-km
Laser-rated for GbE LANs
 62.5/125 microns
Step index
 3/1 dB/km
 160/500 MHz-km
Most common LAN fiber
Single Mode
@1310/1550 nm
 8-9/125 microns
 0.4/0.25 dB/km
 HIGH!
~100 Terahertz
Telco/CATV/long high speed LANs
POF (plastic optical fiber)
650 nm
650 nm
 1 mm
 ~ 1 dB/m
 ~5 MHz-km
Short Links & Cars

48. Cable types : Indoor Outdoor Tight-buffer Ribbon cable Simplex cable
Duplex cable
Distribution cable
Breakout cable
Loose tube cable
Armored cable
Overhead cable
Duct cable
Submarine cable

49. Simplex Cable Mostly used for patch cord and backplane applications.
Simplex cables are one fiber, tight-buffered (coated with a 900 micron buffer over the primary buffer coating) with Kevlar (aramid fiber) strength members and jacketed for indoor use.
Jacket is usually 3 mm (1/8 in.) diameter.
Jacket
Strain relief
Semi-tight tube
Fibre

50. Duplex (Zipcord) Zipcord is two of joined simplex with a thin web.
It's used mostly for patch cord and backplane applications.
Strength members
900 micron buffered fibers
Jacket

51. Distribution Cable
Contain several tight-buffered fibers bundled under the same jacket with Kevlar strength members and sometimes fiberglass rod reinforcement to stiffen the cable and prevent kinking.
Small in size, light in weight and used for short, dry conduit runs, riser and plenum applications.
The fibers are double buffered and can be directly terminated, but because their fibers are not individually reinforced, these cables need to be broken out with a "breakout box" or terminated inside a patch panel or junction box

52. Distribution Cable 900 micron buffered fibers Strength members Jacket
Termination Box (TB)
Strength members
Jacket
Splice tray

53. Breakout Cable Made of several simplex cables bundled together.
A strong, rugged design, but is larger and more expensive than the distribution cables.
Suitable for conduit runs, riser and plenum applications. Because each fiber is individually reinforced, this design allows for quick termination to connectors and does not require termination box.
More economic where fiber count isn't too large and distances too long, because is requires so much less labor to terminate.

54. Breakout Cable Strength members Individual simplex cables
900 micron buffered fibers

55. Loose Tube Cable Fiber Loose Tube 250 micron buffered fibers
Water-blocking and strength members
Jacket

56. Loose Tube Cable
Composed of several fibers inside a small plastic tube, which are in turn wound around a central strength member and jacketed, providing a small, high fiber count cable. The loose tubes filled with gel or water absorbent powder to prevent harm to the fibers from water.
Ideal for outside plant trucking applications.
Can be used in conduits, strung overhead or buried directly into the ground.
Some outdoor cables may have double jackets with a metallic armor between them to protect from chewing by rodents or Kevlar for strength to allow pulling by the jackets.

57. Slotted Ribbon Fiber Cable
This cable offers the highest packing density, since all the
fibers are laid out in rows, typically of 12 fibers, and laid on
top of each other.
Since it's outside plant cable, it's gel-filled for water blocking.

58. Slotted Ribbon Fiber Cable
Core Design
6 slots
Ribbon Size
4 fibers
8 fibers
Fiber Count
Up to 96 cores
Up to 192 cores

59. Armored Fiber Cable
Cable installed by direct burial in areas where rodents are a problem usually have metal armoring between two jackets to prevent rodent penetration. The cable is conductive. Thus, it must be grounded properly.

60. Overhead Fiber Cable

61. Exercise 1:
Let medium 1 be glass and medium 2 be ethyl alcohol. For an angle of incidence of 30 , determine
the angle of refraction .
The numerical aperture
Critical angle of the fiber
Hint:
n1 (glass) = 1.5
n2 (ethyl alcohol) = 1.36

62. Solution:

63. The numerical aperture for the fiber.

64. The critical angle for the fiber.=

65. TUTORIAL
A typical relative refractive index difference for an optical fiber is 1.3% and its core index is given as Determine the NA and critical angle at the core-cladding interface within the fiber. )

66. REFERENCES