Fiber optics and how optical communication takes place.Details regarding how signalling,routing and switching occurs in optical network .A little detail about various equipments used in optical communication.
About optical fiber’s:
Developed in 1970’s an optical fiber (or fiber) is a glass or plastic fiber
designed to guide light along its length by confining as much light as
possible in a propagating form.
Optical fibers are widely used in fiber-optic communication, which
permits transmission over longer distances and at higher data rates than
other forms of wired and wireless communications.
Optical fibers are long, thin strands of very pure glass usually 120 µm in
diameter. They are arranged in bundles called optical cables and used to
transmit light signals over long distances.
The core of a conventional optical fiber is
a cylinder of glass or plastic that runs along
the fiber's length. The core is surrounded
by a medium with a lower index of
refraction, typically a cladding of a different
glass, or plastic.
Cladding is one or more layers of
materials of lower refractive index, in
intimate contact with a core material of
higher refractive index. The cladding causes
light to be confined to the core of the fiber
by total internal reflection at the boundary
between the two.
Optical fiber communication
Optical fibers are based entirely on the principle of total internal
reflection. This is explained in the following picture. Optical fiber is a long,
thin strand of very pure glass about the diameter of a human hair. Optical
fibers are arranged in bundles called optical cables and used to transmit
light signals over long distances.
Fiber-optic transmission of light depends on preventing light from
escaping from the fiber.
Different types of fibers:
Based on the refractive index profile we have two types of fibers
a. Step index fiber
b. Graded index fiber.
Step index fiber
In the step index fiber, the refractive index of the core is uniform
throughout and undergoes an abrupt or step change at the core cladding
Graded index fiber
In the graded index fiber, the refractive index of the core is made to vary in
the parabolic manner such that the maximum value of refractive index is at
the centre of the core.
Based on the modes propagating in optical fiber:
a. Single mode fiber
b. Multi mode fiber
Single mode fiber
Single mode fiber optic cable has a small diametric core that allows only
one mode of light to propagate.
Multi mode fiber
Multimode fiber optic cable has a large diametric core that allows multiple
modes of light to propagate.
Signalling, Routing & Switching in
Transmits information about lines and trunks and information about
other aspects of call handling to control switching equipments.
It can be done as:
COMMON CHANNEL SIGNALLING:
It is a digital communication technique that provides simultaneous
transmission of subscriber data, signalling data and other traffic related
signals throughout a network
CCS is used to transmit to user data and control signals between MS and
BTS and between BTS and MSC and between MSC and GMSC.
Service switching point
Signal transfer point
Service control point
Common channel signalling:
Routing is the exchange service which translates the destination data
received from digit analysis into the physical port which leads to the dialed
destination (outgoing trunk or line).
In telecommunication, an optical switch is a switch that enables signals
in optical fibers or integrated optical circuits (IOCs) to be selectively
switched from one circuit to another.
Switching of the various calls
from one subscriber to the
other is one of the main
functions performed in any of
the telecom network.
In recent years the telephone
switches and data collection
systems have become more
powerful and flexible.
A splicing is to connect one fiber optic cable to another permanently.
Splices are "permanent" connections between two fibers.
It is the attribute of permanence that distinguishes a splice from
Splicing is only needed if the cable runs are too long for one straight pull
or you need to mix a number of different types of cables.
Optical Networking Unit(ONU):
An optical network unit (ONU) is a device that transforms
incoming optical signals into electronics at a customer's premises in order
to provide telecommunications services over an optical fiber network.
ONU provides the subscribers with broadband Internet access.
It is used in combination with an optical line terminal (OLT).
Fiber optic couplers are used to split the input signals into two or more
outputs; they are called splitters in this case.
On the other hand, some types of couplers can be used to combine two
or more inputs into one single output; they are called combiners in this
An optical fiber cable is a cable containing one or more optical fibers.
The optical fiber elements are typically individually coated with plastic
layers and contained in a protective tube suitable for the environment
where the cable will be deployed.
The buffer or jacket on patch cords is often color-coded to indicate the
type of fiber used.
The strain relief "boot" that protects the fiber from bending at a
connector is color-coded to indicate the type of connection. Connectors
with a plastic shell (such as SC connectors) typically use a color-coded shell.
Optical time domain reflectometer(OTDR):
An OTDR is a fiber optic tester characterizing fibers and optical
The aim of this instrument is to detect, locate and measure events at any
location in the fiber optic link.
An OTDR can test a fiber from only one end, that is it operates as a one
dimensional Radar System.
The OTDR technique produces geographic information with regard to
localized loss and reflective events providing a pictorial and permanent
record which may be used as a permanent baseline.
It is well suited to accommodate a
maximum of 96 fibers for various splice
applications such as track (backbone), spur
(branch) or distribution points.
3M’s proven mechanical sealing
technology for the base-to-dome sealing
provides for easy installation & re-entry.
Cable ports can be sealed using
the robust & reliable heat shrink
An optical power meter (OPM) is a device used to measure the power
in an optical signal.
The term usually refers to a device for testing average power in fiber
Other general purpose light power measuring devices are usually called
radiometers, photometers, laser power meters, light meter.
A typical optical power meter consists of a calibrated sensor, measuring
amplifier and display.