Introduction to fiber optics and its Evolution
Basics of optical fiber
Wavelength bands-Transmission windows
Types of optical fibers
Advantages and Disadvantages
Losses in optical fiber
Splitters and types
Field assembly connectors
Cables and types
Splicing and types
Wavelength Division Multiplexing and Types
Communications systems that carry information through a
guided fiber cable are called fiber optic systems.
Use of optical fibers to replace conventional transmission
lines and microwave wave-guide in telecommunication
Light is effectively the same as RF radiation but at a much
higher frequency, theoretically the information-carrying
capacity of a fiber is much greater than that of microwave
As they are not electrically conductive, hence very suitable
for use in areas where electrical isolation and interference
are severe problems.
EVOLUTION OF FIBER
1880 – Alexander Graham Bell
1930 – Patents on tubing
1950 – Patent for two-layer glass wave-guide
1960 – Laser first used as light source
1965 – High loss of light discovered
1970s – Refining of manufacturing process
1980s – OF technology becomes backbone of long
distance telephone networks in NA.
Optical fiber is made from thin strands of either glass or
It has little mechanical strength, so it must be enclosed
in a protective jacket
Often, two or more fibers are enclosed in the same
cable for increased bandwidth and redundancy in case
one of the fibers breaks
It is also easier to build a full-duplex system using two
fibers, one for transmission in each direction
TOTAL INTERNAL REFLECTION
Optical fibers work on the principle of total internal
With light, the refractive index is listed
The angle of refraction at the interface between two
media is governed by Snell’s law:
angle of incidence
The angle of
twice that given
by the numerical
Rayleigh scattering is the
elastic scattering of light or other
electromagnetic radiation by
particles much smaller than the
wavelength of the light.
It can occur when light travels
through transparent solids and
liquids, but is most prominently
seen in gases.
When light moves from a medium of a given refractive
index n1 into a second medium with refractive index n2,
both reflection and refraction of the light may occur.
The relationship between these angles is given by the
law of reflection:
Fiber optic system transmit using infrared light, invisible
to human eye, because it goes further in the optical fiber
at those wavelength.
1260 nm- 1360 nm
1360 nm- 1460 nm
1460nm- 1530 nm
Short wavelength band
1530 nm- 1565 nm
1565 nm- 1625 nm
Long wavelength band
1625 nm- 1675 nm
Ultra long wavelength
Core – thin glass center of the fiber where light travels.
Cladding – outer optical material surrounding the core
Buffer Coating – plastic coating that protects the fiber.
TYPES OF OPTICAL FIBERS
SINGLE-MODE STEP-INDEX FIBER
Used to transmit one signal per fiber.
Used in telephone and cable TV.
They have small cores(9 microns in diameter) .
Transmit infra-red light from laser.
MULTI-MODE STEP-INDEX FIBER
Used to transmit many signals per fiber.
Used in computer networks.
They have larger cores(62.5/50 microns in diameter)
Transmit infra-red light from LED.
MULTI-MODE GRADED-INDEX FIBER
Core diameter : 50/62.5 microns.
Cladding size: 125-140 microns.
Refractive index changes continuously.
Core refractive index is made to vary as a function of the
radial distance from the center of the fiber.
OM1: refer to the commonly used 62.5/125
OM2: refer to the commonly used 50/125 cable.
Both OM1 and OM2 easily supports applications
ranging from Ethernet to gigabit Ethernet.
OM3: Typically this fiber optic patch cable is with
50/125 multimode fiber, with aqua jacket.
They support bandwidth up to 10GB upto 300 meters.
Light weight and small size
Immunity to electromagnetic interference
Lack of EMI cross talk between channels
Lack of sparking
Compatibility with solid state sources
No emission licenses
High investment cost
Need for more expensive transmitters and receivers
Requires special skills
Local Area Networks
Optical Fiber Sensors
Video Surveillance Links
FIBER OPTIC CONNECTORS
Terminates the fibers
Connects to other fibers or transmission equipment
FIBER CONNECTOR TYPE
To avoid an air gap
Ferrule is polished flat, or
Cannot be mated with
the other polish types
Ideal for adjusting OEM systems in production and lab
These attenuators also exhibit low back reflection and good
Fixed attenuators can limit, or attenuate. The amount of light
passing through to the exact level your project.
Used in applications where a pre-determined amount of light
loss is specified.
Most commonly used for test and measurement, optical
sensors, and telecommunications applications.
Modal dispersion is a distortion mechanism occurring
in multimode fibers and other waveguides, in which the
signal is spread in time because
the propagation velocity of the optical signal is not the
same for all modes.
POLARIZATION MODE DISPERSION
A special case of modal dispersion is polarization mode
dispersion (PMD), a fiber dispersion phenomena usually
associated with single-mode fibers. PMD results when two
modes that normally travel at the same speed due to fiber
core geometric and stress symmetry, travel at different
speeds due to random imperfections that break the symmetry
Dispersion is the phenomenon in which the phase
velocity of a wave depends on its frequency.
Dispersion is sometimes called chromatic dispersion
to emphasize its wavelength-dependent nature.
A splitter is a device used to split the cable signal if the
signal must be sent to two or more devices.
Optical splitters are also known as couplers. They are
base on the type of cable management product they will
Performance specifications of the splitters are given by
the ITU- T G671 standard.
FUSED BICONICAL TAPER SPLITTER
These are also known as
Operating wavelength is
1310nm or1550nm and the
passband is 80nm.
The coupling ratio can change
from 1:99 to 50:50.
Low insertion loss.
Low excess loss.
Low polarization related loss.
PLANAR LIGHTWAVE CIRCUITS
These type of splitters are
smaller in footprint.
They offer slightly better losses
across their split ratios than
Low insertion loss.
Low excess loss.
FIELD ASSEMBLY CONNECTORS
Designed for simple and fast
field termination of single fibers,
without polishing or adhesives.
The heart of the Quick-SC fast
connector is a pre-polished
ferrule and a mechanical splice
inside the connector body.
Compatible with conventional
SC and LC connector.
Easy and fast assembly without
Reliable assembly with
Assembly Jig and Fiber Holder
appended to connector kit
Fiber optic "cable" refers to the complete assembly of
fibers, strength members and jacket. Fiber optic cables
come in lots of different types, depending on the number
of fibers and how and where it will be installed. There
are classified as :
Splices are a permanent join of two fibers
Lower attenuation and reflectance than connectors
Stronger and cheaper than connectors
Easier to perform than connectorization
Mass splicing does 12 fibers at a time, for ribbon
Melts the fibers together to form a continuous fiber
Strongest and best join for singlemode fiber
May lower bandwidth of multimode fiber
Mechanically aligns fibers
Contains index-matching gel to transmit light
Equipment cost is low
Per-splice cost is high
Quality of splice varies, but better than connectors
Fiber alignment can be tuned using a Visual Fault
(-45 db to -55 db)
cost – high
No reflection losses
Very low insertion
(0.1 db to .15 db)
WAVELENGTH DIVISION MULTIPLEXING
Data from each TDM channel is loaded on one optical
frequency (or wavelength, ) of a particular wavelength
These wavelengths are then multiplexed onto one fiber
with the help of WDM multiplexers
Other side of the network these wavelengths are
demultiplexed by using either optical filters, gratings or
DENSE WAVELENGTH DIVISION
Can achieve high system capacity by multiplexing more
WDM channels, each with relatively low data rate
Consist of a WDM combined with an optical amplifier, to
allow multiple wavelengths on a single fiber and also
avoid individual regeneration equipment for each
wavelength by use of line amplifiers
COARSE WAVELENGTH DIVISION
o The total CWDM optical span to somewhere near 60 km for
a 2.5 Gbit/s signal.
oCWDM is also being used in cable television networks, where
different wavelengths are used for the downstream (1310
nm) and upstream (1550 nm) signals.
o Signals are not spaced appropriately for amplification by
o Passive CWDM is an implementation of CWDM that uses no
electrical power and separates the wavelengths using band
pass filters and prisms.