Transmission of Data/Voice
over Fiber-Optic link
By Rajesh Chhetry
Objective

The main objective of this paper is to make
a comparative study among different
principles ,technologies and practices that
involve in the transmission of data over
fiber optic link and recommend a
communication system that perfectly meets
the requirements of communication of data
in the current trend and environment.
Introduction

In recent years it has become apparent that
fiber-optics are steadily replacing copper
wire as an appropriate means of
communication signal transmission
 They span the long distances between local
phone systems as well as providing the
backbone for many network systems

This paper is about the different principles
involved in a fiber optic communication.
Fiber Optic technology

fiber-optics use light pulses to transmit
information down fiber lines
 The transmitter accepts coded electronic
pulse information coming from copper wire
 The information is then processed and
translated into equivalently coded light
pulses.

A light-emitting diode (LED) or an
injection-laser diode (ILD) can be used for
generating the light pulses .
 Light pulses move easily down the fiberoptic line because of a principle known as
total internal reflection
Elements of Optical fiber cable





The optic core
An optic cladding,
A buffer material,
A strength material
The outer jacket
Fiber optic applications
(Data)

Backbone architechture for
telecommunication links
 Cable service providers /High speed internet
 Trunk lines
 Monitor power grid systems
 Local area networks
Fiber optics economics

One of the initial economic factors to consider
when converting to fiber-optics is the cost of
replacing wire systems with fiber
 Increased demand for optical fiber has brought the
prices down within competitive range of copper
 In the short term it is often less expensive to
continue using copper cabling for covering
expanded communication needs

In the long term it may be more cost effective to
invest in conversion to fiber-optics .
 This cost effectiveness is due to the relative ease
of upgrading fiber optics to higher speeds and
performance.
 It is generally accepted that customers will need
increased bandwidth as the information highway
grows

Fiber optics will play a pivotal role in this
race since the bandwidth needed for
providing an all-in-one service with
television, telephone, interactive
multimedia, and internet access is not
available in much of the wiring of America.
Single Mode and multimode
fibers

Single mode allows
only one mode of ray
to pass through it’s
core.
 Multi- mode allows
hundreds of rays of
light to propagate
through the core.
Encoding

The source information (such as audio,
video or sonar) comes in many forms .
 The first step is to convert the information
into a bit-stream .
 once the information is stored electronically
and whatever the form, data can be
converted into raw binary data prior to
transmission.
Base Band Modulation

The next step is to modulate the baseband
and this is where, in constructing an optical
communications system, we start making
compromise .
 Different modulation schemes make varying
use of the bandwidth, but the trade-offs will
include distance, compression, BER and
power.

Due to the lack of 'coherent' optical systems
for extracting phase information, optical
communication systems use pulse code
modulation (PCM) schemes to modulate the
baseband .
 There are many PCM techniques
available.HDB3 is the most advanced and
efficient technique developed so far.
HDB3
Light Sources

Leds- produce incoherent light that severely
reduces the obtainable bandwidth .
 Laser Diodes-Lasers produce coherent light
and deliver far higher performance than
LEDs e.g Fabry–perot laser
Recommendations





With reference to the study about the fiber optics
systems , the following communication system
can be recommended for an efficient and reliable
data transmission.
Fabry- perot laser diode
Pulse code modulation technique used for
producing bit streams
Encoded using HDB3 codes
Single Mode step index fiber

This can be a solution for the requirement
of the data-on–demand system
implemented by businesses today.
 The requirement for such a system is high
Bandwidth.
Summary

Based on industry activity, it is evident that
fiber-optics have become the industry
standard for transmission of information.
The choice is not whether to convert to
optical fiber, but rather when to convert to
optical fiber. It is most likely that we will be
able to use it in our local networks in the
days to come.
encoding techniques
 PCM:
pulse code modulation
 samples
of the analog data taken
 each sample quantized
 samples transmited as digital signal
 received samples used to reconstruct analog data
 example:
 samples
voice channels
taken 8000/sec
 quantized to 7 bits
 synch. bit added -> 8 bits
 8 x 8000 = 64000 bps, standard digital voice channel