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INSTRUMENTATION&CONTROLENGINEERINGDEPARTMENT
SARVAJANIKCOLLEGEOFENGG.&TECHNOLOGY
SURAT395001
A PROJECT REPORT ON FIBRE OPTICS
COMMUNICATION
PREPARED BY:
SAURABH DWIVEDI
(807001)
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INDEX
ABSTRACT 3
1 COMPONENT LIST 4
2 COMPONENT DISCRIPTION 6
3 OPTICAL FIBER IN COMMUNICATION 9
4 COMPONENTS OF OPTICAL FIBER COMMUNICATION 13
5 PRINCIPLE OF OPTICAL TRANSMISSION 17
6 OPTICAL TRANSMISSION SECTION 20
7 OPTICAL RECEIVER SECTION 22
8 CIRCUIT WORKING TRANSMITTER 25
9 CIRCUIT WORKING RECEIVER 28
10 ADVANTAGES OVER CONVENTIONAL CABLES 29
11 LIMITATIONS OF OPTICAL FIBER 31
12 APPLICATIONS 32
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ABSTRACT
FIBRE-OPTICS COMMUNICATION
Most reference materials that discuss the historical perspective mention about Indiansmoke signals. None of these primitive systems was secure due to the spreading of the unguided
light. Ideally, a communication system should be secure and should not require installation of a
cumbersome physical media. Fiber optics satisfied these desires, and as early as 1958, fiber-optic
equipment was being focused for use in the factory. The fiber-optic cable is an important element
in the fiber-optic link. Today, in comparison to the early 1970s, the performance of fiber-optic
cable in terms of bandwidth and attenuation is far superior to any electrical cable of similar cost.
Some consider it a problem of fiber optics that the electronics of the fiber-optic transceivers are
unreliable. This is a false, in that the electronics have the same life as any of the other electronic
components used in a network. The need for sharing components or modules is the same for
fiber optics as for any other critical factory-level electronics. Optical fiber is used as glass or
plastic, to contain and guide light wave.
The fiber cable does not transmit electrical current, so it cannot cause ground loops.
Therefore ground differentials caused by lightning-induced transients do not affect the
communication cable. This characteristic is quite an advantage because lightning strikes are a
common phenomenon. A typical fiber-optic cable can allow up to 200 million bits per second
(MBS), while a high-quality coaxial cable is required to achieve the same data rate, but can cover
only shorter distances. The reduction in the number of repeaters is a prime reason for the
telephone companies increasing use of fiber optics. Many control applications require the
operator to perform normal duties in the vicinity of high voltages. The use of fiber allows
isolation of the high voltage from the operators. An advantage of fiber-optics is that the light
signal used for data communication cannot develop a spark above the ignition point, which could
cause ignition in hazardous environments.
The fiber-optic cable is susceptible to noise and it does not generate electromagnetic
interference. It is very simple to install because of light and small size and is suitable for rugged
environments i.e. it can survive high temperatures and other extreme environments.
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1 COMPONENT LIST
AT THE TRANSMITTER SIDE
RESISTORS:-
R1-3K
R2-4K
R3, R4-10K
R5-1K
PRI-1M
CAPACITOR:-
C1-1000 F/16V Electrolytic capacitor
C2-0.047 F-473-ceramic disc type
SEMICONDUCTOR:-
Q1-BEL 187 NPN Transistor
Q2-BEL 188 PNP Transistor
Zener diode
U1-741-Opamp IC
IC socket-8 pin
MISCELLANEOUS:-
Condenser microphone
White LED
9v Battery snap
Red LED
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AT THE RECEIVER SIDE
RESISTORS:-
R1, R2-47K
R3, R4-10K
R5-10
R6-1K
PR1-1M
PR2-10K
CAPACITOR:-
C1-1000 F/16V Electrolytic capacitor
C10-0.047 F Disc type Capacitor
C11, C6-10 F/16V Tantalum capacitor
C7, C8, C9, C2-0.1 F-100KPF-104-Disc Ceramic
C3, C4, C5-100 F/16V-Electrolytic Capacitor
SEMICONDUCTOR:-
IC1-LM741-Opamp IC Socket 8 Pin-2pcs
IC2-LM386-power amp IC
Q1-Photo transistor
MISCELLANEOUS:-
L1-LED 9V Battery
Loud Speaker 8
Transformer 9V
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2 COMPONENT DISCRIPTION
2.1 RESISTOR:-
A resistor is a two-terminal electronic component that produces a voltage across its terminalsthat is proportional to the electric current through it in accordance with Ohm's law:
V=IR
Resistors are elements of electrical networks and electronic circuits and are ubiquitous in most
electronic equipment. Practical resistors can be made of various compounds and films, as well asresistance wire (wire made of a high-resistivity alloy, such as nickel-chrome).
2.2 PRESET:-
It is called variable resistor. We can vary the value according to application. It is used for gain
control and volume control. When we fix the value of preset and mounting on circuit then value
of preset is not applicable to change.
2.3 CAPACITOR:-
(A)Electrolytic capacitor:-An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic conducting
liquid, as one of its plates, to achieve a larger capacitance per unit volume than other types. Theyare often referred to in electronics usage simply as "electrolytics". They are used in relatively
high-current and low-frequency electrical circuits, particularly in power supply filters, where
they store charge needed to moderate output voltage and current fluctuations in rectifier output.
They are also widely used as coupling capacitors in circuits where AC should be conducted but
DC should not. There are two types of electrolytics; aluminum and tantalum.
(B)Ceramic capacitor:-In electronics, a ceramic capacitor is a capacitor constructed of alternating layers of metal and
ceramic, with the ceramic material acting as the dielectric. A ceramic capacitor (especially the
class 2) often has high dissipation factor, high frequency coefficient of dissipation.
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2.4 TRANSISTOR:-
A transistor is a semiconductor device used to amplify and switch electronic signals. It is made
of a solid piece of semiconductor material, with at least three terminals for connection to an
external circuit. A voltage or current applied to one pair of the transistor's terminals changes the
current flowing through another pair of terminals. Because the controlled (output) power can bemuch more than the controlling (input) power, the transistor provides amplification of a signal.
Today, some transistors are packaged individually, but many more are found embedded in
integrated circuits.
2.5 INTEGRATED CIRCUIT:-
In electronics, an integrated circuit (also known as IC, chip, or microchip) is a miniaturized
electronic circuit (consisting mainly of semiconductor devices, as well as passive components)
that has been manufactured in the surface of a thin substrate of semiconductor material.
Integrated circuits are used in almost all electronic equipment in use today and haverevolutionized the world of electronics. Computers, cellular phones, and other digital appliances
are now inextricable parts of the structure of modern societies, made possible by the low cost of
production of integrated circuits.
2.6 LED:-
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lampsin many devices, and are increasingly used for lighting. Introduced as a practical electronic
component in 1962,early LEDs emitted low-intensity red light, but modern versions are
available across the visible, ultraviolet and infrared wavelengths, with very high brightness.
When a light-emitting diode is forward biased (switched on), electrons are able to recombine
with electron holes within the device, releasing energy in the form of photons. This effect is
called electroluminescence and the color of the light (corresponding to the energy of the photon)
is determined by the energy gap of the semiconductor. An LED is often small in area (less than1 mm2), and integrated optical components may be used to shape its radiation pattern .[3]LEDs
present many advantages over incandescent light sources including lower energy consumption,
longer lifetime, improved robustness, smaller size, faster switching, and greater durability andreliability. LEDs powerful enough for room lighting are relatively expensive and require more
precise current and heat management than compact fluorescent lamp sources of comparable
output.
Light-emitting diodes are used in applications as diverse as replacements for aviation lighting,
automotive lighting (particularly brake lamps, turn signals and indicators) as well as in traffic
signals. The compact size, the possibility of narrow bandwidth, switching speed, and extremereliability of LEDs has allowed new text and video displays and sensors to be developed, while
their high switching rates are also useful in advanced communications technology. Infrared
LEDs are also used in the remote control units of many commercial products includingtelevisions, DVD players, and other domestic appliances.
http://en.wikipedia.org/wiki/LED#cite_note-2http://en.wikipedia.org/wiki/LED#cite_note-2http://en.wikipedia.org/wiki/LED#cite_note-2http://en.wikipedia.org/wiki/LED#cite_note-27/30/2019 Fiber Optic Communication Report
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2.7 SEMICONDUCTOR:-
(A)OPAMP-LM741:-An Operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltage amplifier
with a differential input and, usually, a single-ended output. An op-amp produces an outputvoltage that is typically hundreds of thousands times larger than the voltage difference between
its input terminals.
Operational amplifiers are important building blocks for a wide range of electronic circuits. They
had their origins in analog computers where they were used in many linear, non-linear and
frequency-dependent circuits. Their popularity in circuit design largely stems from the fact the
characteristics of the final elements (such as their gain) are set by external components with little
dependence on temperature changes and manufacturing variations in the op-amp itself.
(B)IC-LM386:-The LM386 (aka JRC386) is an integrated circuit consisting of a low voltage audio power
amplifier. It is suitable for battery-powered devices such as radios, guitar amplifiers, and
hobbyist projects. The IC consists of an 8 pin dual in-line package (DIP-8) and can output 0.5
watts power using a 9-volt power supply.
(C)PHOTO DIODE:-A photodiode is a type of photo detector capable of converting light into either current or
voltage, depending upon the mode of operation.
A photodiode is a PN junction or PIN structure. When a photon of sufficient energy strikes thediode, it excites an electron, thereby creating a free electron and a (positively charged electron)
hole. If the absorption occurs in the junction's depletion region, or one diffusion length away
from it, these carriers are swept from the junction by the built-in field of the depletion region.
Thus holes move toward the anode, and electrons toward the cathode, and a photocurrent is
produced.
2.8 LOUD SPEAKER:-
A loudspeaker (or "speaker") is an electro acoustic transducer that converts an electrical signal
into sound. The speaker moves in accordance with the variations of an electrical signal and
causes sound waves to propagate through a medium such as air or water.
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3 OPTICAL FIBERS IN COMMUNICATION
3.1 Introduction
Optical fibers are one of the worlds most influential scientific developments from the latter half
of the 20th century. Normally we are unaware that we are using them, although many of us dofrequently. The majority of telephone calls and internet traffic at some stage in their journey will
be transmitted along an optical fiber. Why has the development of fibers been given so much
attention by the scientific community when we have alternatives? The main reason is bandwidth
fibers can carry an extremely large amount of information. More indirectly, many of the
systems that we either rely on or enjoy in everyday life such as banks, television and newspapers
as are themselves dependent on communication systems that are dependent on optical fibers.
Fiber-optic communication is a method of transmitting information from one place to another by
sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave
that is modulated to carry information.
An optical fiber is a glass or plastic fiber that carries light along its length. Optical fibers are
widely used in fiber optic communications, which permits transmission over longer distances
and at higher bandwidths because light has higher frequency than any other form of radio signal.
Light is kept in the core of the optical fiber by total internal reflection. Fibers are used instead of
metal wires because signals travel along them with less loss, and they are also immune to
electromagnetic interference.
3.2 Fundamentals of Fibers
The fundamental principle that makes optical fibers possible is total internal reflection. This is
described using the ray model of light as shown in figure 1.
Figure 1 - Total Internal Reflection
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From Snells Law we find that refraction (as shown by the dashed line) can only occur when the
angle theta1 is large enough. This implies that as the angle is reduced, there must be a point
when the light ray is reflected, where theta1 = theta2.
The angle where this happens is known as the critical angle and is:
3.3 CONSTRUCTION OF FIBERS
In fibers, there are two significant sectionsthe core and the cladding. The core is part where the
light rays travel and the cladding is a similar material of slightly lower refractive index to cause
total internal reflection. Usually both sections are fabricated from silica (glass). The light within
the fiber is then continuously totally internally reflected along the waveguide.
Figure 2: Structure of Fiber
When light enters the fiber we must also consider refraction at the interface of the air and the
fiber core. The difference in refractive index causes refraction of the ray as it enters the fiber,
allowing rays to enter the fiber at an angle greater than the angle allowed within the fiber asshown in the figure 3.
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Figure 3 - Acceptance Angle
3.4 CLASSIFICATION OF OPTICAL FIBERS:-
Optical fibers are classified into three types based on the material used, number of modes and
refractive index.
3.4.1. Based on the materials used:-
a. Glass fibers:They have a glass core and glass cladding. The glass used in the fiber is ultra pure, ultra
transparent silicon dioxide (SiO2) or fused quartz. Impurities are purposely added to pure glass
to achieve the desired refractive index.
b. Plastic clad silica:
This fiber has a glass core and plastic cladding. This performance though not as good as all glass
fibers, is quite respectable.
c. Plastic fibers:They have a plastic core and plastic cladding. These fibers are attractive in applications where
high bandwidth and low loss are not a concern.
3.4.2. Based on the number of modes:-
a. Single Mode fiber:
When a fiber wave-guide can support only the HE11 mode, it is referred to as a single mode
wave-guide. In a step index structure this occurs when the wave-guide is operating at v
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mode fibers have small size and low dopant level (typically 0.3% to 0.4% index elevation over
the lading index.)
In high silica fibers the wave-guide and the material dispersion are often of opposite signs. This
fact can be used conveniently to achieve a single mode fiber of extremely large bandwidth.
Reduced dopant level results in lower attenuation than in multimode fibers. A single mode waveguide with its large and fully definable bandwidth characteristics is an obvious candidate for long
distance, high capacity transmission applications.
b. Multimode fiber:It is a fiber in which more than one mode is propagating at the system operating wavelength.
Multimode fiber system does not have the information carrying capacity of single mode fibers.
However they offer several advantages for specific systems. The larger core diameters result in
easier splicing of fibers. Given the larger cores, higher numerical apertures, and typically shorter
link distances, multimode systems can use less expensive light sources such as LED s.Multimode fibers have numerical apertures that typically range from 0.2 to 0.29 and have core
size that range from 35 to100 micro-meters.
3.4.3. Based on refractive index:-
a. Step index fiber:
The step index (SI) fiber consists of a central core whose refractive index is n1, surrounded by a
lading whose refractive index is n2, lower than that of core. Because of an abrupt index changeat the core cladding interface such fibers are called step index fibers.
b. Graded index fibers:
The refractive index of the core in graded index fiber is not constant, but decreases gradually
from its maximum value n1 to its minimum value n2 at the core-cladding interface. The ray
velocity changes along the path because of variations in the refractive index. The ray propagating
along the fiber axis takes the shortest path but travels most slowly, as the index is largest along
this path in medium of lower refractive index where they travel faster. It is therefore possible for
all rays to arrive together at the fiber output by a suitable choice of refractive index profile.
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4 COMPONENTS OF OPTICAL FIBER
COMMUNICATION:
4.1 Transmitters: -
Fiber optic transmitters are devices that include an LED or laser source, and signal conditioning
electronics, to inject a signal into fiber. The modulated light may be turned on or off, or may be
linearly varied in intensity between two predetermined levels.
Figure:-The basic components of an optical fiber communication
The transmitter is physically close to the optical fiber and may even have a lens to focus the light
into the fiber. Lasers have more power than LEDs, but vary more with changes in temperature
and are more expensive. The most common wavelengths of light signals are 850 nm, 1,300 nm,
and 1,550 nm
4.2 Fiber:-
It is the medium to guide the light form the transmitter to the receiver.
4.3 Receivers:-
Fiber optic receivers are instruments that convert light into electrical signals. They contain a
photodiode semiconductor, signal conditioning circuitry, and an amplifier at the receiver end.Several types of photodiodes include p-n photodiodes, a p-i-n photodiodes, and avalanche
photodiodes. Metal-semiconductor-metal (MSM) photo detectors are also used due to their
suitability for circuit integration in regenerators and wavelength-division multiplexers.
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4.4 Amplifiers
The transmission distance of a fiber-optic communication system has traditionally been limitedby fiber attenuation and by fiber distortion. By using opto-electronic repeaters, these problems
have been eliminated. These repeaters convert the signal into an electrical signal, and then use a
transmitter to send the signal again at a higher intensity than it was before. Because of the highcomplexity with modern wavelength-division multiplexed signals (including the fact that they
had to be installed about once every 20 km), the cost of these repeaters is very high.
An alternative approach is to use an optical amplifier, which amplifies the optical signal directly
without having to convert the signal into the electrical domain. It is made by doping a length of
fiber with the rare-earth mineral erbium, and pumping it with light from a laser with a shorterwavelength than the communications signal (typically 980 nm). Amplifiers have largely replaced
repeaters in new installations.
4.5 Wavelength-division multiplexing
Wavelength-division multiplexing (WDM) is the practice of multiplying the available capacity
of an optical fiber by adding new channels, each channel on a new wavelength of light. This
requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer(essentially a spectrometer) in the receiving equipment. Arrayed waveguide gratings are
commonly used for multiplexing and demultiplexing in WDM. Using WDM technology now
commercially available, the bandwidth of a fiber can be divided into as many as 160 channels to
support a combined bit rate into the range of terabits per second.
4.6 Dispersion
For modern glass optical fiber, the maximum transmission distance is limited not by directmaterial absorption but by several types of dispersion, or spreading of optical pulses as they
travel along the fiber. Dispersion in optical fibers is caused by a variety of factors. Intermodal
dispersion, caused by the different axial speeds of different transverse modes, limits theperformance of multi-mode fiber. Because single-mode fiber supports only one transverse mode,
intermodal dispersion is eliminated.
In single-mode fiber performance is primarily limited by chromatic dispersion (also called group
velocity dispersion), which occurs because the index of the glass varies slightly depending on the
wavelength of the light, and light from real optical transmitters necessarily has nonzero spectral
width (due to modulation). Polarization mode dispersion, another source of limitation, occurs
because although the single-mode fiber can sustain only one transverse mode, it can carry thismode with two different polarizations, and slight imperfections or distortions in a fiber can alter
the propagation velocities for the two polarizations. This phenomenon is called fiberbirefringence and can be counteracted by polarization-maintaining optical fiber. Dispersion
limits the bandwidth of the fiber because the spreading optical pulse limits the rate that pulses
can follow one another on the fiber and still be distinguishable at the receiver.
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Some dispersion, notably chromatic dispersion, can be removed by a 'dispersion compensator'.
This works by using a specially prepared length of fiber that has the opposite dispersion to thatinduced by the transmission fiber, and this sharpens the pulse so that it can be correctly decoded
by the electronics.
4.7 Regeneration
When a communications link must span a larger distance than existing fiber-optic technology iscapable of, the signal must be regenerated at intermediate points in the link by repeaters.
Repeaters add substantial cost to a communication system, and so system designers attempt to
minimize their use.
Recent advances in fiber and optical communications technology have reduced signal
degradation so far that regeneration of the optical signal is only needed over distances of
hundreds of kilometers. This has greatly reduced the cost of optical networking, particularly overundersea spans where the cost and reliability of repeaters is one of the key factors determining
the performance of the whole cable system. The main advances contributing to theseperformance improvements are dispersion management, which seeks to balance the effects of
dispersion against non-linearity; which use nonlinear effects in the fiber to enable dispersion-freepropagation over long distances.
4.8 MODES AND PROPAGATION OF LIGHT IN FIBERS
Also crucial to understanding fibers is the principle of modes. A more in-depth analysis of the
propagation of light along an optical fiber requires the light to be treated as an electromagnetic
wave (rather than as a ray).
Figure 4Modes
The solid line is the lowest order mode shown on figure 4. It is clear that according to the ray
model the lowest order mode will travel down a given length of fiber quicker than the others.
The electromagnetic field model predicts the opposite that the highest order mode will travel
quicker. However, the overall effect is still the same if a signal is sent down the fiber as several
modes then as it travels along the fiber the pulse will spread out, this can lead to the pulses
merging and becoming indistinguishable.
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Figure 5: Propagation of light in fibers
The propagation of light is as shown in figure 5. When light ray enters the core with an anglestrikes the surface of cladding whose refractive index is less than that of core. As the incidence
angle on surface of the cladding is greater than or equal to critical angle total internal
reflection takes place. Hence the ray is reflected back into the core in the forward direction. This
process continues until it reaches other end of the cable.
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5 PRINCIPLE OF OPTICAL TRANSMISION
5.1 Index of refraction:-
This is the measuring speed of light in respective medium. It is calculated by dividing speed of
light in vacuum to the speed of light in material. The RI for vacuum is 1, for the cladding
material of optical fiber it is 1.46, the core value of RI is 1.48(core RI must be more than
cladding material RI for transmission) it means signal will travel around 200 million meters per
second. It will travel 12000 km in only 60 seconds. Other delay in communication will be due to
communication equipment switching and decoding, encoding the voice of the fiber.
5.2 Snell's Law:-
In order to understand ray propagation in a fiber. We need one more law from high school
physics. This is Snell' law. n1 sin 1 = n2 sin 2
Where n denotes the refractive index of the material. 1/2 are angles in 1/2 respective
medium. Higher Refractive Index means denser medium. 1) When light enters in lighter mediumfrom denser it inclines towards normal. 2) When light enters in denser medium from lighter it
inclines away to normal.
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5.3 Critical Angle:-
If we consider we notice above that as the angle 1 becomes larger and larger so does the angle
2. Because of the refraction effect 2.becomes larger more quickly than 1 .At some point 2
will reach 90 while 1 is still well less than that. This is cal led the critical angle. When 1is
increased further then refraction ceases and the light starts to be reflected rather than refracted.
Thus light is perfectly reflected at an interface between two materials of different
refractive index if:
1. The light is incident on the interface from the side of higher refractive index.
2. The angle is greater than a specific value called the critical angle. Glass refractive index is
1.50 (critical angle is 41.8); Diamond critical angle is 24.4 degree.
5.4Total Internal reflection (TIR):-
When light traveling in a dense medium hits a boundary at a steep angle (larger than the "critical
angle for the boundary), the light will be completely reflected. This phenomenon is called total
internal reflection. This effect is used in optical fibers to confine light in the core. Light travels
along the fiber bouncing back and forth off of the boundary; because the light must strike the
boundary with an angle greater than the critical angle, only light that enters the fiber within a
certain range of angles can travel down the fiber without leaking out. Total internal. Reflection
occurs when light enters from higher refractive index to lower refractive index material, i.e. from
glass to air total internal reflection is possible but it is not possible in air to glass.
Figure-1 (optical rays leaks out from core i.e. is loss)
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Figure-2 (Optical rays reflected back due to TIR) Fig-2
If we now consider above Figures we can see the effect of the critical angle within the fiber. In
Figure 2 we see that for rays where angle 1 is less than a Critical value then
the ray will propagate along the fiber and will be bound within the fiber. In Figure 1 we see
that where the angle 1 is greater than the critical value the ray is refracted into the cladding and
will ultimately be lost outside the fiber. This is loss.
5.5 Acceptance Cone:-
When we consider rays entering the fiber from the outside (into the end face of the Fiber) we see
that there is a further complication. The refractive index difference between the fiber core and
the air will cause any arriving ray to be refracted. This means that there is a maximum angle for a
ray arriving at the fiber end face at which the ray will propagate. Rays arriving at an angle less
than this angle will propagate but rays arriving at a greater angle will not. This angle is not acritical angle as that term is reserved for the case where light arrives from a material of higher
RI to one of lower RI. (In this case, the critical angle is the angle within the fiber.) Thus there is a
cone of acceptance at the end face of a fiber. Rays arriving within the cone will propagate and
ones arriving outside of it will not. The size of acceptance cone is function of difference of RI of
core and cladding.
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6 OPTICAL TRANSMITTER SECTION
The optical transmitter section of our system consists of transducer, voltage amplifier, power
amplifiers, regulator circuit, light emitting diode (LED).
6.1 MICROPHONE:-
Acoustic transducer is microphone which picks up acoustic signal and converts that into
electrical signal. In order to process the audio signal, the microphone is required. There are
variety of transducer are available in the industry. Different Microphone has different
characteristics like frequency response, directivity, sensitivity etc. some of microphone are
Dynamic microphone, carbon microphone, crystal microphone. We have use condenser type
microphone here.
Condenser microphone depends on its action on the capacitance between two electrodes or
conducting plates. If one of the capacitance between the plates is moveable, sound waves strikingthese plated vary the capacitance between the plates and these variations are in step with the
sound waves. Charging and discharging currents produce oscillatory voltage, which are applied
small audio amplifier.
The diaphragm is usually of duralumin and may be thin as 0.0025cm to 0.005cm. The separation
between two plates is generally 0.0025cm to 0.005cm. The capacitance between the plates is
about 300pf for a diaphragm of 38cm of diameter. A potential difference of about 150 V is
applied between two plates. Condenser microphone has good efficiency response from 30Hz to 9
KHz.
6.2 VOLTAGE AMPLIFIER:
The audio signal coming from microphone is too small in its amplitude, which makes it
necessary to amplify that up to some usable limits. For amplification process there are some
devices available i.e. transistor, FETs, Audio amplifier ICs etc.
As audio frequency is limited to 20 Hz to 20 KHz region we have to use device which can
produce satisfactory output at these frequencies.
We have used here op amp IC741, which is voltage amplifier IC when we applied audio signal
from the microphone. This signal is weak signal so the IC 741 will amplify this signal up tosome limit. This is about 20V. This output of voltage amplifier stage is given to the power
amplifier stage.
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6.3 POWER AMPLIFIER:
The signal amplify by the amplifying voltage is not strong enough to drive load. So, we
introduce on more stage which can give rise tour signal and which is capable to drive load.
We have use push pull amplifier as the second stage. As shown in figure, Q1 AND Q2 transistoris used as push pull amplifier which gives the gain of 100. By pass capacitor C5 100F reduce
supply line. Output of the amplified signal is taken from emitter two transistors Q1 BEL 187
NPN & Q2 BEL 188 PNP which is fade to the drive stage.
6.4 LIGHT SOURCE:
Light source for fiber optic systems must convert electrical energy from the computer or terminal
circuits feeding them to optical energy in a way that allows the light to be coupled effectively to
the fiber. Two such sources currently in production the surface light emitting diode and the
injection laser diode.
6.5 LIGHT EMIITING DIODE:
A cross section of a LED surface is shown in figure. It emits light over a relatively broad
spectrum, and it disperses the emitted light light over a rather large angle. This cause the LED to
couple much less power into a fiber with a given acceptance angle than does the ILD. Currently,
LEDs are able to couple about 100 microwatts of power into a fiber with a numerical aperture of0.2 or more and a coupling efficiency of about 2%. The principle advantages of LEDs are low
cost and high reliability.
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7 OPTICAL RECIVER SECTION
Optical receiver is the circuit, which receives optical waves (beam), convert it into electrical
variation by mean of optical, amplify it and reproduce the original information signal.
7.1 OPTICAL DETECTOR:
Optical detector is an electronic device, which senses the optical signal and convert into
electrical signal generally two types of devices are available:
1: photo diode
2: photo transistor
Main difference between photo diode and photo transistor is the current gain the some amount
of light both devices produce current gain times more current in photo transistor then photo
diode but the switching speed of photo diode s more than phototransistor Photo transistor hasoutput current in mA but switching times is in microsecond. In communication system high
speed is required so photo transistor are used two types of Photo transistor are there PNP and
NPN. Here we have used NPN types
7.2 VOLTAGE AMPLIFIER STAGE:
As already discussed in transmitter part, the weak signal from detector is fed to the voltage
amplifier in order to boost the signal. Two stages are used to provide amplifier to vary weak
signal. Here we use operational amplifierIC-741.
7.3 GAIN COTROL STAGE:
In receiver circuit the gain is controlled by presets. Here we have used two presets for gain
control.
7.4 POWER AMPLIFIER:
The LM-38X series power amplifier is designed for use in low voltage consumer electronics
applications such as AM-FM radio amplifier, intercoms and power converts. OF the various
chips in the series the 386 is an ideal choice for this project because the gain of the amplifier can
be controlled by external circuitry. This amplifier features supply voltage range from 5V to 12V.Voltage gain from 26db to46db and ground reference input the distortion possible with LM386
CAN BE AS LOW AS 0.02% with gain of 26db and 80hm load. When operated with a gain of
26db the LM386 is characterized by a typical bandwidth of 300MHz. when pin no1and8 are
open a 1.35k resistor connects these pins internally. This open configuration holds the gain at
20db placing a capacitor C6 across pin no 1and8 will bypass the internal resistor and push the
gain up to 200(46db)
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7.5 LOAD SPEAKER:
To reproduce the information signal transmitted from the transmitted earlier, we need some
Transducer device which can convert electrical signal to voice signal which is the actual
Information signal
Here our information signal was audio signal and to reproduce the audio energy from the
Electrical signal, we need a loud speaker. There are also many types in loudspeakers like Horn
type, moving coil type etc. we have crystal type etc. we have used 80hm horn type loud speaker
that is directly radiating type loudspeaker.
We can listen to the received audio signal using the loudspeaker. Thus our transmitted Audio
signal is transmitted, received and again converted to acoustic signal.
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8 CIRCUIT WORKING
TRANSMTER
8.1 MICROPHONE
In the transmitter circuit, the condenser microphone picks up the sound signal. These signals are
converted into electrical variation in the transmitter circuit the resistor R2 &capacitor C3 are
used as filter circuit the output of microphone (electrical signal) is Given to the pin no.2 of IC
741 And 9V of the battery given to the pin no.3 of 741 IC Through voltage divider network of
resistor R3 & R4. The IC used in inverting mode with signal supply using divider network of
resistor. The output of 741 is available on pin No.6 the potentiometer or preset which value is 1
MOhm is used to control the gain of IC741. Hence it is also act as a volume control
8.2 PUSH-PULL AMPLIFIER
The transistor Q1 (NPN) &Q2 it is possible to obtain a full cycle output across a load using Half
cycle of operation from each transistor. In the positive half cycle, the transistor Q1 (NPN) will be
biased into conduction, with a resulting half-cycle of signal across ground & R6 resistor. During,
negative half cycle the transistor Q2 (PNP) will be biased into Conduction, with a resulting half
cycle of signal across ground &R6ressor. The output of two transistor pair or PUSH-PULL
amplifier as shown in below figure.
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The output of PUSH-PULL amplifier is given to the diode Zd.
The zener diode is used as a regulator or as a reference voltage.
In the above figure simple regulator designed to a fixed voltage across the white LED.
For values of applied voltage greater than required to turn the zener diode ON, the Voltage
across LED will be maintaining Vz volts. If zener diode is employed reference Voltage, it will
provide a level for compression against other voltage.
The output of Zener diode is Vz volts is given to photo diode &the final output is through Light.
When we pass the audio signal &convert into electrical variation through condenser Microphone
because the variation in electric signal the light of photo diode is vary &the Final signal is
transmitted through light.
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9 CIRCUIT WORKING
RECEIVER
9.1 PHOTO DETECTOR:
At the receiver side photo transistor is used as a detector, which is to convert light signal
variation into electrical signal variation. In this circuit we use (NPN) photo transistor, which is
used to collect photon from light signal. Because of this photon the resistance of this photo
transistor converts this light variation into electrical signal, whereas the photo transistor has
output current in mili amperes and switching time is in micro seconds.
9.2 VOLTAGE AMPLIFIER:
This variation of electric signal is given to the op-amp or (IC-741) which is in inverting mode
with single supply using divider networksR3 & R4. This output of photo transistor is given to thepin no. 2 or non inverting pin of IC 741. IC 741 is used for voltage amplification.
9.3 GAIN CONTROL:
PR1 &PR2 are the 1Mho preset & 1K ohm preset respectively. PR1 is used to control of IC741.
& act as a volume control. PR2 also acts as a volume and gain control.
9.4 POWER AMPLIFIER:
The output of IC741 is given to IC LM 386. IC LM386 is a power amplifier designed for use in
low voltage consumer. The gain is internally set to 20 db keep external part count low, but theadditional of capacitor C6 between pin no-1 & pin no-8 will increase the gain to any value up to
200. The output of the IC386 is given to the loud speaker & C8 & R5 is RC circuit & it is used
for filtering R1 & C10 is also used as a filter circuit.
9.5 LOUD SPEAKER:
The output of IC386 is given to the loud speaker. Loud speaker is a reproduced information
signal. Means loud speaker converts electrical signal onto sound signal. We can listen to receive
audio signal using this loud speaker. Thus our transmitted audio signal transmitted, received &
again converted into the original acoustic form.
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10 ADVANTAGES OVER CONVENTIONAL CABLES
The choice between optical fiber and electrical (or copper) transmission for a particular
system is made based on a number of trades-offs. Optical fiber is generally chosen for systems
requiring higher bandwidth or spanning longer distances than electrical cabling canaccommodate. The main benefits of fiber are its exceptionally low loss, allowing long distances
between amplifiers or repeaters; and its inherently high data-carrying capacity, such thatthousands of electrical links would be required to replace a single high bandwidth fiber. Another
benefit of fiber is that even when run alongside each other for long distances, fiber cables
experience effectively no crosstalk, in contrast to some types of electrical transmission lines.
In short distance and relatively low bandwidth applications, electrical transmission is often
preferred because of its
Lower material cost, where large quantities are not required.
Lower cost of transmitters and receivers. Ease of splicing. Capability to carry electrical power as well as signals. Ease of operating transducers in linear mode.
a. Wide Bandwidth:Optical fibers offer greater bandwidth due to the use of light as carrier. The frequency range
used for glass fiber communication extends from 2*e14Hz to 4*e14Hz. Hence optical fibers are
suitable for high speed, large capacity telecommunication lines.
b. Low Loss:In a coaxial cable attenuation increases with frequency. The higher the frequency of information
signals the greater the loss, whereas in an optical fiber the attenuation is independent of
frequency. They offer a loss of0.2 dBm/km, allowing repeater separation up to 50Km or more.
c. Freedom from electromagnetic interference:Optical fibers are not affected by interference originating from power cables, railways and radio
waves. They do not limit unwanted radiation and no cross talk between fibers exists. These
fibers make an ideal transmission medium when EMI (Electro Magnetic Immunity) is increased.
d. Non conductivity:Optical fibers are non-conductive and are not effective by strong electromagnetic interference
such as lighting. These are usable in explosive environment.
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e. Small diameters and less weight:Even multi fiber optical cables have a small diameter and are light weight, and flexible optical
fiber cables permit effective utilization of speech and can also be applicable to long distance use
are easier to handle and install than conventional cables.
f. Security:Fiber optic is a highly source transmission medium. It does not radiate energy that can be
received by a nearby antenna, and it is extremely difficult to tap a fiber and virtually impossible
to make the tap undetected.
g. Safety:Fiber is a dielectric and does not carry electricity. It presents no sparks or fire hazards. It does
not cause explosions, which occur due to faulty copper cable.
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11 LIMITATIONS OF OPTICAL FIBER:
1. The terminating equipment is still costly as compared to copper wire.
2. Delicate so has to be handled carefully.
3. Communication is not totally in optical domain, so repeated electric to optical to electrical
conversion is needed.
4. Optical amplifiers, splitters, MUX-DEMUX are still in development stages.
5. Tapping is not possible. Specialized equipment is needed to tap a fiber.
6. Optical fiber splicing is a specialized technique and needs expertly trained manpower.
7. The splicing and testing equipments are very expensive as compared to copper equipments.
8. Bending Cables
9. Gamma Radiation
10. Electrical Fields
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12 APPLICATIONS:-
Military applications Mobile applications Telecommunications Satellite communications Under sea transmission cable Internet & Broadband applications Computer applications Electrical power companies Optical sensor system Local area networks Electronic media Public network applications Civil application Consumer application Industrial application
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