DEP5313-FIBER OPTIC
COMMUNICATION SYSTEM
TOPIC 1: FIBER OPTIC CHARACTERISTICS
COURSE LEARNING OUTCOME
1. Apply the concepts of light properties in the
fiber optic communication system. (C3, PLO1)
2. Solve problems regarding light transmission in
fiber optic communication link. (C3, PLO2)
3. Design fiber optic communication link using link
budget. (C5, PLO4)
4. Display the ability to handle systematically the
testing instruments for fiber optic
communication system. (P4, PLO5)
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.
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
VLF
105
Telephone
Lines
105
LF
104
106
MF
103
107
HF
102
AM Radio
108
109
1010
VHF UHF SHF
10
1
10-1
1011 1012
EHF
10-2 10-3
Broadcast TV
Fiber optic transmission
wavelengths
1013 1014
Satellite
Downlink
1015 1016
IR
10-4
10-5
VR
UV
10-6
10-7
Fiber Optic
Wavelengths
Electromagnetic Frequency Spectrum
Visible
Light
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
3. Infrared
- Light wavelength
which human
eye will respond
- human eye
- harmless to the
body.
Bandwidth of Light Wave
Ultraviolet
Band of light wavelengths that are too short to be
seen by the human eye.
Infrared
• Band of light
wavelengths that are
too long to be seen by
the human eye.
Visible
• Band of light
wavelengths to which
the human eye will
respond.
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
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
c is the speed of light
f is the
frequency of
the light in hertz
(Hz)
The characteristics of light (properties)
The light characteristic is useful in an optical link :
i) Light travel in a straight line
ii) 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 6.626 x10-34 Joules.
iii) Power(Watts, dBm) , Wavelength (m), frequency (Hz)
iv) Light travels in vacuum or air with a speed of is 3x108 m/s
v) Light travels in materials with slower speed then 3x108 m/s
The characteristics of light (properties)
vi) Charge less - does not interact with other light, can go
through each other.
vii) Can be visible or invisible.
viii) Light can be refracted if its travel through two different
medium. Refraction is the deflection of light.
ix) 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.
x) Light can be polarized using polarization (angle: degree)
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.
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).
c
n
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
n1 sin  1  n2 sin  2
Index of Refraction
SUBSTANCE
Solids at 20 °C
Diamond
Glass, crown
Ice (0°C)
Sodium chloride
Quartz
Crystalline
Fused
Liquids at 20 °C
Benzene
Carbon disulfide
Carbon tetrachloride
Ethyl alcohol
Water
Gases at 20 °C
Air
Carbon dioxide
Oxygen, O2
Hydrogen, H2
INDEX OF REFRACTION, n
2.419
1.523
1.300
1.544
1.544
1.458
1.501
1.632
1.461
1.362
1.333
1.000 293
1.000 45
1.000 271
1.000 139
Refraction
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
c  sin ( n1 )
1
n2 – index of refraction medium 1
n1 – index of refraction medium 2
Refraction
Example of critical angle condition
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).
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
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.
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 𝜽𝒂
• 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.
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.
Related Formula
c
 Index of Refraction, n 
v
 Snell’s Law,
n1 sin 1  n2 sin  2
 n2 

 Critical Angle,  c  sin 
 n1 
1
 Acceptance Angle,
 Numerical Aperture,

  sin 1 n12  n22

NA  sin   n12  n22
N.A.  n1 2
RECAP
Problem - 1
• Given the index of reflection of diamond is 2.419 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 2.248 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 1.544 and the velocity of light in a
vacuum is 2.99 x 108 m/s. Calculate the velocity of light in all
three material?
RECAP
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
incident = 12°
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?
n2 sin  2
sin 1 
n1

1.33sin 31

 0.69
1.00
1  44

 2  tan 1 2.0 3.3  31
RECAP
Problem – 6
A step index fiber has a core diameter of 100μm and a refractive
index of 1.480. The cladding has a refractive index of 1.460.
Calculate the numerical aperture of the fiber and acceptance
angle from air.
Solution:
The numerical aperture is
NA = (n12 – n22)1/2
= (1.4802 - 1.4602) 1/2
= 0.2425
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.
TIR occurred
0i<0c
(a)
TIR not occurred
(b)
0i<0c
 c  sin 1 
 n2
 n1

 1.00 

  sin 1 
  24.4
 2.42 

 n2
 c  sin 
 n1

 1.33 

  sin 1 
  33.3
 2.42 

1
Tutorial
Given an index of reflection of glass is 1.523 and an index
of reflection of air is 1.003. Determine the acceptance
angle if the light is moving from air towards glass.
Light Propagation in a Fiber Optic Cable
: Propagation modes
MULTI
MODE
Types of FO
SINGLE
MODE
Step index
Graded
index
Cable Size
SMF
MMF
•9
• 125 micron
•50/125
•62.5/125 micron
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.
Single Light Propagation
Cladding
Core
Light
propogation
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.
Multimode step-index
Kevlar
Light
Source
Cladding
D
C
A
B
Core
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.
Multimode graded-index
Cladding
Core
Light
Propogation
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.
Light Propagation in a Fiber Optic
Cable : Index Profiles
Light Propagation in a Fiber Optic Cable :
Index Profiles
Summary
The Structure of Fiber Cables
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.
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 gelfilled 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
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
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)
Fiber Types and Typical Specifications
Core/Cladding
Attenuation
Bandwidth
Applications/Notes
Multimode
@850/1300 nm
@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)
1 mm
@ 650 nm
@ 650 nm
~ 1 dB/m
~5 MHz-km
Short Links & Cars
Cable types :
Indoor
•Tight-buffer
•Ribbon cable
•Simplex cable
•Duplex cable
•Distribution cable
•Breakout cable
Outdoor
•Loose tube cable
•Armored cable
•Overhead cable
•Duct cable
•Submarine cable
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
Duplex (Zipcord)


Zipcord is two of joined simplex with a thin web.
It's used mostly for patch cord and backplane
applications.
Jacket
Strength
members
900 micron
buffered fibers
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
Distribution Cable
Termination Box
(TB)
900 micron
buffered fibers
Strength members
Splice tray
Jacket
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.
Breakout Cable
Individual
simplex
cables
Strength
members
900 micron
buffered fibers
Loose Tube Cable
Loose
Tube
Fiber
250 micron buffered
fibers
Loose tube
Water-blocking and
strength members
Jacket
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.
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.
Slotted Ribbon Fiber Cable
Core Design
6 slots
6 slots
Ribbon Size
4 fibers
8 fibers
Fiber Count
Up to 96 cores
Up to 192 cores
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.
Overhead Fiber Cable
Exercise 1:
• Let medium 1 be glass and medium 2 be ethyl alcohol. For
an angle of incidence of 30 , determine
i. the angle of refraction .
ii. The numerical aperture
iii. Critical angle of the fiber
•Hint:
•n1 (glass)
= 1.5
•n2 (ethyl alcohol) = 1.36
Solution:
n1
sin 1  sin  2
n2
1.5
sin 30  0.5514  sin  2
1.36
 2  sin 1 0.5514  33.47
• The numerical aperture for the fiber.
NA 

2
1
n
n
1.5
 0.633
2
2
2
 1.36 
2
•
The critical angle for the fiber.
Θc
1
 n2

n
 1




=
sin
=
 1.36 
sin 

 1 .5 
1
 65.05
TUTORIAL
• A typical relative refractive index difference for an optical
fiber is 1.3% and its core index is given as 1.46. Determine
the NA and critical angle at the core-cladding interface
within the fiber.
)
REFERENCES
Agrawal, Govind P. (2010). Fiber-Optic Communication Systems. (Fourth Edition).
Wiley Series. (ISBN : 978-0-47050511-3).
Downing , James N. (2005). Fiber-Optic Communications, Thomson Delmar
Learning. (ISBN: 1-4018-6635-2).
George Kennedy, Bernard Davis. (2006). Electronics Communication Systems.(4th).
McGraw Hill.
Jim Hayes, (2010). Fiber Optics. Technician’s Manual, Fourth Edition. Thomson
Delmar Learning.
Joseph C. Palais, (2005) Fiber Optic Communications. Fifth Edition. Pearson /
Prentice Hall. (ISBN 0130085103, 9780130085103).