OPTICAL COMMUNICATION AND NETWORKING PRESENTATION

NAVAMI SURESH,GPTC KADUTHURUTHY
SUBMITTED BY,
NAVAMI SURESH
LECTURER IN KADUTHURUTHY
OPTICAL COMMUNICATION
&
NETWORKING
1

OPTICAL FIBER COMMUNICATION
 Fiber-optic communication is a method of transmitting
information from one place to another by sending pulses of
light through an optical fiber.
 APPLICATIONS
1. Medical:-Used as light guides, imaging tools and also as
lasers for surgeries
2. Telecommunications- Fiber is laid and used for transmitting
and receiving purposes
3. Used in CCTV surveillance cameras
4. Used in data link for computer networks
2

Structure of Optical Fiber
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 Fiber Optic Cable consists of four parts
1. Core
2. Cladding
3. Buffer
4. Jacket
4

 Fiber Optic Core: the inner light-carrying member with a high
index of refraction.
 Cladding: the middle layer, which serves to confine the light to
the core. It has a lower index of refraction.
 Buffer:The outer layer, which serves as a "shock absorber" to
protect the core and cladding from damage.The coating usually
comprises one or more coats of a plastic material to protect the
fiber from the physical environment.
 JACKET :Fiber optic cable’s jackets are available in different
colors that can easily make us recognize the exact color of the
cable we are dealing with.
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REFRACTION
 When a light ray goes from a denser transmission medium
to a rarer one or vice versa, then its direction changes at the
interface of the two medium.This phenomenon is called
refraction of light.
7

REFRACTIVE INDEX
 Refractive index, measure of the bending of a ray
of light when passing from one medium into another
 Refractive index is also equal to the velocity of light c of a given
wavelength in empty space divided by its velocity v in a
substance, or n = c/v.
 Refractive index n(Refractive index of medium 1 w.r.t
medium2)=sin i /sin r
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CRITICAL ANGLE
 Critical angle is defined as the angle of incidence that
provides an angle of refraction of 90-degrees
 sinθc = n2/n1
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Principle of light transmission in a Fiber
 For light propagating from denser medium to rarer medium,
if the angle of refraction is 90 degrees, the corresponding
angle of incidence is called critical angle.
 If a light ray is an incident at the interface of two media with
an angle greater than the critical angle, it is completely
reflected back to the denser medium.This phenomenon is
called total internal reflection.
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Optical fibers use total internal reflection to transmit
light. It has a solid core of dense glass surrounded by a
less dense cladding.The light ray passing through the
inner core is reflected back instead of being refracted to
the rarer cladding.
13

CONDITIONS FOR TOTAL INTERNAL
REFLECTION
 For total internal reflection to take place
(i) light must travel from a denser medium to a rarer medium
(ii) the angle of incidence inside the denser medium must be
greater than the critical angle.
14

NUMERICAL APERTURE
 NA is a measure of the light gathering ability of a fiber.
The Numerical Aperture (NA) of a fiber is defined as
the sine of the largest angle an incident ray can have for
total internal reflectance in the core
15

ACCEPTANCE ANGLE
 The maximum angle at or below which a ray of light
can enter through one end of the fiber still be total
internal reflection is called as acceptance angle.The
cone is referred as acceptance cone.
16

PROBLEMS
 CALCULATETHE SPEED OF LIGHT IN ICE,IF
REFRACTIVE INDEX OF ICE IS 1.31
n=c/v
c=3x10^8 m/s
n=1.31
v=(3x10^8)/1.31
=2.29x10^8m/s
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DIFFERENT TYPES OF FIBRE BASED ON
REFRACTIVE INDEX & TRANSMISSION MODE
Refractive
Index
1. Step Index
2. Graded Index
Transmission
Mode
1. Single Mode
2. Multi Mode
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SINGLE MODE
 Only one path is available.
 Core diameter is small
 Used for long distance communication
 Fabrication is difficult and costly
22

Multi Mode
 More than one path is available
 Core radius is larger compared to single mode
 Easy to launch power in to optical fiber
23

STEP INDEX FIBER
 The refractive index of the core is uniform throughout and
undergoes on abrupt change at the core cladding boundary
 The path of light propagation is zig- zag in manner
GRADED INDEX FIBER
 The refractive index of the core is made to vary gradually such
that it is maximum at the center of the core.
 The path of light is helical in manner
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DIFFERENT TYPES OF FIBER MATERIALS
 Optical fibers are used for transmitting light signals over long
distances with minimal loss of signal.They are made from
materials that can guide light effectively.
 The most common materials used for optical fibers are glass
and plastic.
Glass Optical Fibers
 Silica Glass : Most common material due it’s excellent
optical properties, low attenuation, and high-temperature
resistance. Used in most telecommunications and high-speed
data transfer applications
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 Doped Silica: Silica glass doped with materials like
germanium (Ge), phosphorous (P), or boron (B) to modify the
refractive index.
Plastic Optical Fibers
 Polymethyl Methacrylate (PMMA):used in short-
distance applications due to their ease of handling, flexibility,
and lower cost.
 Fluorinated Polymers: These polymers have lower
attenuation than PMMA and are used in specialized applications
requiring higher performance over medium distances
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ADVANTAGES OF OPTICAL FIBERS
1. High Bandwidth: Can transmit significantly higher amounts
of data compared to copper cables.
2. Low Attenuation and Long Distance : Much lower signal
loss
3. High-SpeedTransmission
4. Immunity to Electromagnetic Interference
5. Security : Difficult to tap into a fiber-optic cable without
being detected
6. Easier Installation
7. Lower Operating Costs
28

MODULE-2
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OPTICAL SOURCES
 Optical sources refer to devices that emit light or optical
radiation
 FEATURES OF OPTICAL SOURCES
 Size and configuration: Compatible with launching light
into fiber(i.e physical dimensions to suit the optical
fiber).For to couple large amount of power into an optical
fiber, the emitting area should be small.
 High coupling efficiency or have high optical output power
(i.e Adequate output power into the fiber)
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 Narrow spectral width (or line width)
 Stability and efficiency
 The power requirement for its operation must be low.
 High Reliability and low cost
 It must be possible to operate the device continuously at a
variety of temperatures for many years.
31

 Main Optical sources for communication are
1. Incoherent sources: Light Emitting
Diode(SLED,ELED,SLD)
2. Coherent Sources : LASER diode(DFB,DBR)
32

LIGHT EMITTING DIODE(LED)
 Semiconductor diodes which emits visible or invisible light when
forward biased
 Emits light when voltage is applied
 When forward biased free electrons in the conduction band
recombines with the holes in the valence band and releases
energy in the form of light.
 The process of emitting light in response to the strong electric
field or flow of electric current is called electroluminescence.
 The construction of LED is similar to the normal p-n junction
diode except that gallium, phosphorus and arsenic materials are
used for construction instead of silicon or germanium materials.
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SYMBOL OF LED
35

SURFACE EMITTING & EDGE EMITTING
LEDS
PARAMETER SURFACE EMITTING EDGE EMITTING
Light
Emission
Direction:
Emit light perpendicular to
the surface
Emit light parallel to the surface of the
semiconductor chip
Beam Shape: The light emitted is
usually broad and
somewhat diffuse,
resulting in a wider
beam angle.
narrower beam with higher
directionality.
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PARAMETER SURFACE EMITTING EDGE EMITTING
Applications Commonly used in
indicators, displays, and
lighting applications where a
wide emission pattern is
beneficial.
Commonly used in optical
fiber communications, laser
diodes
Manufacturing: Generally simpler and
cheaper to manufacture
compared to edge-emitting
LEDs
More complex and
expensive to manufacture
Reliability Less Reliable Highly reliable
System Performance Low High
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SURFACE EMITTING LED
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EDGE EMITTING LED
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 Light is emitted from the edge of active layer.
 It consists of two optical guiding layers.
 Both guiding layers has refractive index lower than active
region and higher than surrounding material.
 If NumericalAperture is low, Edge emitting LED couples
more power than surface emitting LED.
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Modulation of LED
1. Modulating LEDs involves varying their light output by
controlling the electrical input using techniques such as
AM, PWM, and digital modulation.
2. The choice of modulation method depends on the
application requirements, including speed, efficiency, and
complexity.
3. Advances in LED technology and driver circuits continue
to enhance the capabilities and applications of LED
modulation.
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Modulation of LED
 Methods to achieve modulation
 PulseWidth Modulation (PWM):PWM controls the
LED brightness by switching it on and off at a high frequency.
The average power delivered to the LED is varied by
changing the duty cycle
 Analog Modulation :The current through the LED is
varied continuously to change its brightness.This can be done
by adjusting the voltage applied to the LED.
 Frequency Modulation (FM):The frequency of the
LED's on/off switching is varied
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 Out of these three phenomena transmission and reflection is
of less importance to optical sources and detectors.
 Reflection and transmission are typically considered loss
mechanisms.
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Types of Semiconductors
DIRECT BANDGAP INDIRECT BANDGAP
Generally preferred for
making optical sources.
Cannot be used to
manufacture optical sources.
When an electron
recombines with holes
energy is emitted in form of
light
When an electron
recombines with holes
energy is emitted in form of
light & heat
Example is Gallium
Arsenide (GaAs).
Example is Silicon and
Germanium.
49

Theory of Laser action – absorption and emission of
radiation , population inversion, stimulated emission
 LASER is Light Amplification by Stimulated Emission
of Radiation.
 The process by which electrons in the ground state absorbs
energy from external energy sources to vibrate into the
higher energy level is called as absorption.
 Principle of LASER:Absorption and Emission of
Radiation
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 There are two energy levels namely E1 and E2 for electrons.
 E1 is the ground state or lower energy state of electrons.
 The electrons in the ground state are called lower energy
electrons or ground state electrons
 E2 is the excited state or higher energy state of electrons.
 The electrons in the excited state are called higher energy
electrons or excited electrons
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 When photons or light energy equal to the energy difference
of the two energy levels (E2 – E1) is incident on the atom.
 The ground state electrons gains sufficient energy and
vibrates from ground state (E1) to the excited state (E2).
 Excited state is an unstable state.
 The lifetime of electrons in excited state is of short
period(10 ns).
 After 10 ns, the excited electrons return to the lower energy
state or ground state by releasing energy in the form of
photons
53

SPONTANEOUS EMISSION
 This process is a naturally occurring process and is
called as spontaneous emission.
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 But in spontaneous emission no control over excited electron
and it produces incoherent light
 Hence for producing coherent light principle of stimulated
emission is used.
55

PRINCIPLE OF LASER
 LASER-LIGHT AMPLIFICATION BY STIMULATED
EMISSION OF RADIATION
 Main principle of LASER IS STIMULATED EMISSION
OF RADIATION
 Stimulated emission involves a process called pumping.
 The electrons in the ground state are vibrated to the excited
states by providing extra energy from energy sources like
electric field(current source) called as electrical pumping
or light called as optical pumping
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STIMULATED EMISSION
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 When incident photon interacts with the excited electron, it
forces the excited electron to return to the ground state
 The excited electron release energy in the form of light while
falling to the ground state
 Two photons are emitted.
 One is due to the incident photon and another one is due to
the energy release of excited electron.
 Hence from one photon, two photons are released.This is
light amplification.
58

 All the emitted photons in stimulated emission have the same energy,
same frequency, same polarization and are in phase.
 The number of photons emitted in the stimulated emission depends
on the number of electrons in the higher energy level or excited state
and the incident light intensity.
 The process of achieving greater population in higher energy state
than the lower energy state in order to increase the intensity of light
emitted is called as population inversion.
 To achieve population inversion, atoms must be continuously excited
from a lower energy level to a higher energy level and the process by
which the atoms are excited to a higher energy level is
called pumping.
59

LASER diode structure and Radiation
pattern
60

 A laser diode is a semiconductor device that transmits
coherent and highly focused light through a process called
stimulated emission.
 It comprises a p-n junction, where electrons and holes
combine, releasing energy as photons.
 The aim of active layer in between p and n-type layers is to
increase the area of electron and hole combination.
 The laser output is taken from active region of the laser
diode.
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OPTICAL DETECTORS
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PHOTODETECTION
 Photo detector can be defined as a device that is used to detect light
radiations by absorption
 The basic principle of the photo detector is that when an incident
light or radiation falls on the surface of detector and get absorbed, it
converts it into electrical signals.
 Photo detector acts as a reversed biased p-n junction. Let’s
understand how the photo detector works-
 There are three process works in the operation of the photo detector:
 Absorption
 Transportation of Carriers
 Extraction of Carriers As Photocurrent
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 Absorption-In this process, the light energy falls on the photo
detector which gets absorbed by it . Electron-Hole pairs are
generated
 Transportation-In this process, the generated charge carriers
get transported across all the absorption regions.
 Extraction of Carriers As Photocurrent-
 The current is generated mainly because of the photons that
fall on the photo detector, it is called photocurrent.
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PIN Photodiode
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 As the name implies, these photodiodes consist of an un
doped intrinsic layer between two highly doped p-
n junctions.
 Photons hit the intrinsic layer of the PIN diode , they are
absorbed and generate electron-hole pairs. Photons are
absorbed at Intrinsic region .That is the importance of
Intrinsic region.
 The movement of these charge carriers generates a
photocurrent.
 It gives better performance than the common photodiodes.
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AVALANCHE PHOTODIODE
69
AVALANCHE REGION
INTRINSIC REGION

 In the case of p-n photodiodes and p-i-n photodiodes, the output
photocurrent is very small because of the very limited gain.
 To provide a large gain, the avalanche photodiode is used. It is
useful in low light conditions
 Light absorbed in depletion region of P-N junction creating
electron-hole pairs.
 These electron-hole pairs are swept across the depletion region
by reverse bias.
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 The key feature of an APD is the high electric field in the
depletion region.As the electron (or hole) accelerates under
this field, it gains enough kinetic energy and collides with
other atoms, creating additional electron-hole pairs.This
process is called Impact Ionization.
 It generates large number of carriers from single photon ,
effectively amplifying signal

COMPARE PIN AND AVALANCHE DIODE
PARAMETER PIN DIODE AVALANCHE DIODE
MECHANISM When light strikes the
intrinsic region, electron-
hole pairs are generated
When light generates electron-hole
pairs, the high electric field in the
depletion region causes these carriers
to accelerate and collide with atoms,
creating additional electron-hole
pairs through impact ionization.
RESPONSETIME Faster response since no
multiplication process
involved
Slower response since multiplication
process involved
NOISE Lower noise since there is no
Higher due to avalanche
TEMPERATURE STABILITY Low High
INTERNAL GAIN Low HIGH
REVERSE BIASVOLTAGE Lower Reverse BiasVoltage Higher Reverse biasVoltage
SENSITIVITY Lower since it has no
internal gain
Higher due to avalanche
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OPTICAL COMMUNICATION AND NETWORKING PRESENTATION

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