1. UNDERSTANDING
FIBER OPTIC
PRINCIPLES

2. 1.0 UNDERSTANDING FIBER OPTIC PRINCIPLES
Fiber Optic communication is the method by which information signals are transmitted from one
place to another using light signals in a fiber optic cable. This is analogous to the transmission of
electric signals in a copper cable.
How do you use fiber cable to carry light signals? Imagine using a torch in a straight corridor to
shine light from one end to the other. There will be no problem.
Now imagine if the corridor is curved. The light will not reach the other end unless there is well
positioned mirror to reflect the light.
If the corridor now has many twisting bends, we can get the light to travel to the other end by
properly positioning more mirrors as appropriate all the way to the other end and the torchlight will
be received at the other end.
By continuously reflecting the light we got it to “transmit” from one end to the other end. This is
similar to what happens in a fiber optic cable. How do we get the light to continuously reflect in a
fiber optic cable without using “mirrors”?
To achieve this reflection, we go back to our 0’Level physics - Light theories and Snell’s law in
particular. One of Snell’s laws tells us that when light passes though two media with two refractive
indexes the following occur:
 Reflection
 Refraction
 Absorption
 Scattering

3. • 1.1 Reflection:
• 1.2 Refraction:
The Angle of Refraction, θ2 is determined by a factor which is called the index of Refraction (or
Refractive index). If Refractive index n1 (see diagram above) is greater than n2, the light ray is bent
away from the normal (NN). if the n1 is less than n2, the ray is bent towards the normal (NN).
We are interested in the situation where n1 is greater than n2 i.e. when light is passing from a
medium of higher refractive index to a medium of lower refractive index.
Air has lower refractive index than ordinary glass. When glass is purified (i.e impurities in it are
removed) the purified glass has a higher refractive index than ordinary glass. These are the basic
materials used in a fiber optic cable.

4. θc
B
B’n1
n2
N
N
1.3 Total Internal Reflection:
When the angle of incidence is increased, at a certain angle, called the Critical Angle, the refracted light
ray travels between the two interfaces.
Beyond the Critical Angle, Total Internal Reflection takes place.
In other words, if the angle of incidence is always higher than the critical angle, total internal reflection will
always take place. This is the condition that allows light signals entering into a fiber Optic cable to get
continuously reflected.
If we have a material (core) of very high refractive index (very pure glass) surrounded by a material with a
low refractive index (impure glass) and we introduce light signals at an angle of incidence higher than the
critical angle, then the light signal will suffer continuous total internal reflection and therefore propagate in
the core.

5. Glass Cladding
Primary Buffer
Secondary Buffer to 900μm
Glass Core
CABLE STRUCTURE
2.0 HOW FIBER OPTIC CABLE TRANSMIT LIGHT SIGNALS
The basic Fiber Optic Cable structure is shown below:
Glass Core: Very pure glass, high refractive index, carries most of the light.
Glass Cladding: Impure glass, low Refractive index, bends the light and confines it to the core.
Primary Buffer: Provides the first layer of mechanical protection.
Secondary Buffer: This coating protects the primary coating. How
The diagram below, showing the cross section of the F.O. cable illustrates how the cable structure shown above guides light
rays introduced into the glass core.
• The cladding allows total internal reflection if the launch angle is greater than the critical angle and the light ray
propagates down the F. O. cable glass core.
•The Refractive index of the core is higher than that of the cladding
•The light rays are maintained by total internal reflection at the interface of the glass core and cladding.
•The buffer also prevents any light loss by absorption.

6. 3.0 THE ADVANTAGES OF FIBER OVER COPPER
For the planning of your network, there are two primary options – FIBER or COPPER.
The option to use depends on your existing network (if any) and your future networking needs.
While considering your future networking needs, look at your bandwidth/speed requirements,
distances to be covered, operating environment, your budget etc.
For now, copper is more popular than Fiber and much more predominant in structured cabling
systems. However, Fiber is gaining in popularity. It is becoming the fastest-growing option for
new cabling installations and upgrades especially backbone that require the transmission of huge
amounts of data.
In some cases, copper is still a preferred option for horizontal and desktop sections of your
structured cabling network.
In other cases, Fiber is the de-facto choice when you need to go long distances, need high
bandwidth and, complete immunity to electrical interference.
Low Attenuation and greater distance.
Due to the nature of fiber optic propagation (uses light signals) very little signal loss occurs
during transmission, so data can move at higher speeds and cover greater distances. For
structured cabling, Copper has a distance limitation of 100m while fiber distances range from
250m to 100kilometers depending on the type of cable and Transmitter/Receiver parameters.
Greater Bandwidth
For now, Copper (Cat 5e & Cat 6) is good up to 1 Gigabit. Cat 7 and Cat 7a which may go up to 10
Gigabit has not been fully developed and deployed.
On the other hand fiber has a ready bandwidth of 10 Gigabit and beyond. No competition!

7. c. Security
Your data is safe with a fiber cable. It does not radiate signals and is extremely difficult
to tap. If the cable is tapped, it’s very easy to know because the cable will be leaking
light causing the link to fail.
d. Immunity and Reliability
Fiber provides extremely reliable data transmission. It’s immune to many
environmental factors that affect copper. The fiber is made of glass, which is an
insulator, so no electric current can flow through it. It is immune to electromagnetic
interference and radio-frequency interference (EMI/RFI), crosstalk, impedance
problems, etc. You can run fiber cable next to industrial equipment without worry.
e. Weight and Durability
Fiber compared to Copper is lightweight, thin and more durable. Its smaller size makes
it easier to handle and it takes up less space when installed.
Although fiber splicing and termination are more difficult and expensive, advancements
in technology and increased demand has reduced these problems.
f. Future Upgrading
With the rapid developments in information technology fuelling an almost insatiable
demand for bandwidth, Copper is getting close to its limit. Fiber is the way to go and
should be used where bandwidth demands will increase.
No wonder our telecom companies use only fiber for their backbone connections.

8. 4.0 COMPONENTS OF A BASIC FIBER OPTIC LINK
A B CD E FG H GF E B AC DI KLJC FF K J I FFH C
A - Server / Desktop / Laptop / Switch / Router
B - Network Interface Card
C - RJ 45 Connector
D - UTP Patch Cable
F - Fibre Connector
G - Fibre Patch Cable
H - Fibre Coupler / Adapter
I - Pig-tail
J - Patch Panel
K - Splice Tray
L - Fibre Cable
E - Transceiver or Media Converter
BASIC COMPONENTS OF A FIBRE OPTIC LINK
4.1 Fiber Optic Transmitter & Receiver (Transceivers)
The basic Fiber Optic link consists of a transmitter at one end of the link and a receiver at the other end. It operates by transmitting
in one direction from the transmitter at one end to the receiver at the other end. This is called Simplex Transmission.
When there is a transmitter at the other end transmitting to a receiver at this end, on a separate cable simultaneously, we have
Duplex Transmission.
When the transmitter and receiver are incorporated into a single module we have a Transceiver.
The most commonly used optical transmitters are semiconductor devices such as Light Emitting Diodes (LED) and Laser
Diodes. LEDs are used in low end devices while laser diodes are used in high end devices.

9. 4.2 Fiber Optic Cables
There are different ways of classifying Fiber Optic Cables:
By the mode of transmission, giving rise to Multimode and Singlemode cables(determined by the
size of the glass core)
By the arrangement/configuration of individual fiber strands in the cable.
By the installation method of the cable.
4.2.1 Multimode and Singlemode Cables:
Multimode fiber cables have a large core diameter and can support multiple pathways of light.
The core diameter is either 50 or 62.5 microns and the cladding diameter is 125 microns. The
62.5micron core fiber cable (usually with orange jacket) is more popular here. The 50 micron
core fiber cable usually comes with an aqua-blue jacket.
In contrast the Singlemode fiber cable has a smaller core diameter and can support only one
pathway of light. The core diameter is 9 microns. The Singlemode cable usually comes with a
yellow jacket.
What do these different core diameters get you?
Distance: You get 50 times more distance with Singlemode than with Multimode.
Bandwidth: You also get higher bandwidth with Singlemode.
4.2.2 Cables Types by their Configuration
There are 3 main categories of fiber cables when grouped by configuration:
Tight Buffer Distribution Cable
Tight Buffer Breakout Cable

10. iii. Gel-filled Loose Tube Cable
4.2.3 Cable Types by Installation method
These come as:
Indoor Cable
Outdoor Cable
Armoured Cable
Aerial Cable
4.3 Fiber Optic Patch Panels
Fiber optic Patch Panels are also known as Fiber Distribution Panels.
A fiber patch panel usually is composed of two parts, the compartment that contains the fiber optic couplers
(or adapters) and, the compartment that contains the fiber optic splice trays and also holds the excess cable.
There are two main types of fiber optic patch panels – the wall mounted type and the rack mounted type.
4.4 Fiber Optic Connectors
A fiber optic connector terminates the end of a fiber optic cable and enables connection and disconnection.
The connector mechanically couples and aligns the core of the fiber so that light can pass with minimal loss
of light due to reflection or misalignment of the fibers.
There are many different types of fiber connectors but the three most popular types in our market are:
ST Connector- Uses a bayonet style locking system.
SC Connector- Features a moulded body and a push-pull locking system.
LC Connector- A small-form factor connector that looks like a mini SC connector.
They all come as either Singlemode or Multimode although the ST connector is not usually used for
Singlemode.
Others less popular (in our environment) fiber connectors include the FC, MTRJ, MU, SMA, SMC, MT, etc.

11. 5.0 FIBER OPTIC TOOLS & TEST EQUIPMENT
5.1 Fiber Optic Tools
a. Kevlar Cable Cutter
b. Jacket/Fiber Stripper
c. No-Nik Fiber Optic Stripper
d KVM Wipes
e. Pump Fluid Dispenser
f. Isopropyl Alcohol
g. Fiber Optic Connector Crimping Tool
h. Carbide – Tip Scribe
i. Connector Heater Oven
j. Polishing Disk
k. Polishing Film
l. Polishing Plate
m. Epoxy
n. Syringe
o. Fusion Splicer
p. Cleaver
q. Protection Sleeves

12. p. Cleaver
q. Protection Sleeves
5.2 Fiber Optic Test Equipment
a. Continuity Tester
b. Fiber Optic Scope or Fiberscope
c. Fiber Optic Light Source
d. Fiber Optic Power Meter
e.
Optical Time Domain Reflectometer
(OTDR)

13. 6.1 Stripping and Cable Preparation
Open the connector bags and separate the individual parts:
-Boot
-Crimp Ring
-Connector body with Ferrule
Put the boot on the cable before stripping
Strip the fiber jacket back 1½” with the jacket stripper
Strip the 900um buffer with No-Nik fiber stripper to a length of ½”
Finally cut Kevlar to 3/8” with the Kevlar scissors.
The bare fiber will need to be cleaned with alcohol and a KVM wipe.
6.2 Connector Assembly
Mix the epoxy on a clean surface and thoroughly coat the stripped fiber with the epoxy.
Carefully insert the fiber into the ferrule from the back using a twisting motion if
necessary.
Alternatively use a syringe to apply the epoxy inside the ferrule ensuring a bit shows at
the tip of the ferrule.
Slide the cable into the back of the connector making sure that the Kevlar fans back to
fit between the cable jacket and the inside of the metal sleeve.
Crimp the rear shell of the connector with the F.O. Crimping Tool.
Slide boot up to fit tight to the back of the connector.

14. 6.3 Curing the Epoxy
There are two methods used for curing the Epoxy:
The Heater Oven cure method. Using the Heater Oven, the epoxy can be cured in 15-20 minutes.
The other method is to cure at room temperature for 24 hours.
6.4 Scoring the fiber
After the epoxy curing there is excess fiber protruding from the tip of the ferrule. The excess fiber has to be removed
by scoring with the Carbide-Tip Scribe Tool.
Score the fiber as close as possible to the tip of the ferrule with the Carbide Tip Scribe Tool.
After scoring, you will gently pull on the fiber to remove the excess fiber.
6.5 Polishing the Connector
Lay the appropriate Polishing Puck or Disk on the polishing film, then insert the connector ferrule into the Polishing
Puck or Disk.
Lay the polishing film flat on the polishing plate with the grit side up.
Holding the polishing disk, without applying pressure on the connector, you polish by moving the connector using
continuous figure 8 movements on the polishing film.
The first stage is the Air Polish Stage. You use the 5µm polishing film to remove the glass burr on the top of the
connector.
After the burr is removed you will be ready for the final polishing of the connector. This removes all scratches and
chips from the glass.
After polishing, wipe the tip with alcohol and the Kim Wipe.
Inspect the connector using the microscope to ensure the connector face is free of chips, scratches and cracks.
6.6 Testing of the completed fiber optic cable
Continuity Test.
Ferrule Clarity Test.
Insertion Loss Test.

15. 7.0 FIBER OPTIC SPLICING
The joining of two fiber optic cables is referred to as splicing. Joining lengths of optical fiber
cable is more complex than joining electrical wire or cable.
The ends of the fibers must be carefully cleaved and then carefully joined together with the
cores perfectly aligned.
There are two methods used for fiber optic splicing:
 Fusion Splicing; and,
 Mechanical Splicing.
Fusion Splicing provides a fast, reliable, permanent, low loss fiber to fiber connection. The
fibers are melted or fused together by heating the fiber ends using an electric arc.
Mechanical Splicing on the other hand are not as permanent as fusion splicing. The loss
attributable to mechanical splicing is much higher.
For Mechanical Splicing, you will need:
Alignment Sleeve;
Clamping Mechanism;
Index Matching Gel.
7.1 Fusion Splicing
Fusion splicing is the process of joining or fusing two optical fibers end-to-end with an electric
arc. It fuses the two fibers such that light passing through the joint or splice is neither
scattered nor reflected back by the splice.

16. Singlemode fibers are the most convenient to splice. Multimode fibers can be harder to
fusion splice as the larger core (5.5 to 7 times larger), with many layers of graded-index
profile are sometimes harder to align. For fusion splicing, the following tools are
required:
 Fusion Splicer
 Cleaver
 Fiber Cable Stripper
 No–Nik Fiber Stripper
 Protector Sleeves
 KVM Wipes
 Pump Fluid dispenser
 Isopropyl alcohol
Procedures to follow:
Prepare the cable (strip jacket). Clean cable.
Prepare the fibers (strip buffer coating). Clean fiber.
Cleave fiber
Insert protector sleeve. Place both stripped fiber ends in the Fusion Splicer and run
appropriate Fusion Splicer programme.
Inspect Splice.
Align protector sleeve on the fused joint and place in the protector sleeve heater on the
Fusion Splicer.
Inspect finished splice.