Fiber Optic Communication Report

7/30/2019 Fiber Optic Communication Report

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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.
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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.


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.


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

Fiber Optic Communication Report

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