OPTICAL FIBERS:
STRUCTURES,
WAVEGUIDING,
AND
FABRICATION
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The Nature of Light
1. Light is a transverse, electromagnetic wave that can be seen by
humans.
2. The wave nature of light was first illustrated through experiments on
diffraction and interference.
3. Like all electromagnetic waves, light can travel through a vacuum.
4. The transverse nature of light can be demonstrated through
polarization.
5. The speed of light depends upon the medium through which it travels.
6. Intensity is the absolute measure of a light wave's power density
7. Brightness is the relative intensity as perceived by the average human
eye.
8. The frequency of a light wave is related to its energy and color.
9. The wavelength of a light wave is inversely proportional to its
frequency.
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Spherical and plane wave fronts
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Field distributions in plane E&M waves
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The Structure of an Electromagnetic Wave. Electric and magnetic fields are
actually superimposed over the top of one another but are illustrated separately
for clarity in illustration. The z-direction can be considered to be either a
representation in space or the passing of time at a single point.
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Amplitude Fluctuation in an Electromagnetic Wave. Here both the electric field
and the magnetic field are shown as a single field oscillating about a locus of
points which forms the line of travel.
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Basic Optical Laws and Definitions
Refractive Index
The ratio of the speed of light in a vacuum to that in
matter is known as the refractive index or index of
refraction n of the material and is given by
n=c/v
Typical values of n are
1.00 for air,
1.33 for water,
1.45 for silica glass
2.42 for diamond.
larger value of n = Denser material
lower value of n = Less denser material
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Index of Refraction
n1<n2<n3
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Refraction and reflection
Reflection of light
• Some part of the light reflected when strikes
on a surface
• Laws of reflection of light
– Angle of incident is equal to angle of reflection
– The incident ray, the normal and the reflected ray
all lies in same direction
Refraction of light
• When light enters from one medium to other
medium
– Direction and velocity are changed
– It is called refraction of light
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Refraction and reflection
– When light passes from rare to dense
medium, it bends towards the normal
– When light passes from dense to rare
medium, it bends away from the normal
– Law of refraction is
• The incident ray, the normal, and the
refracted ray at the point of incident all lies in
the same plane
• The ratio of the sine of angle incidence to the
sine of angle of refraction is always constant
– This ratio is called refractive index
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Refraction and reflection
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Diagrams illustrating reflection and refraction of light, viewed as waves and
particles.
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Refraction and reflection
• Snell,s Law
– Snell discovered the relationship between
the refractive indices of the materials and
the sine of the angles as:
• n1 sinф1 = n2 sinф2
– If the angle of refraction is 90 then it is
equal to 1 so
• Sinфc =n2 / n1
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Refraction and reflection
• Total internal reflection
– When light passes from denser medium
to rarer medium it bends away from the
normal
– The incident angle for which angle of
refraction is 90° is called critical angle
– If incident angle becomes more than
critical angle all the light will reflect back
to the same denser medium
– Such a phenomenon is called total
internal reflection
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A
Angle of Incidence
B
Glass
Air
Angle of Refraction
Critical Angle
C
Glass
Air
Glass
Air
Angle of Incidence
90 0
= Angle of Reflection
Glass
Air
D
The critical angle of incidence.
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Polarization Components of Light
•Light is composed of one or more transverse
electromagnetic waves
•Electric field (called an E field) and a magnetic field
(called an H field) component.
•In a transverse wave the directions of the vibrating
electric and magnetic fields are perpendicular to each
other and are at right angles to the direction of propagation
of the wave
•Vibrations in the electric field are parallel to one another at
all points in the wave, so that the electric field forms a plane
called the plane of vibration
•All points in the magnetic field component of the wave lie
in a plane that is at right angles to the electric field plane.
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Unpolarized light
An ordinary light wave is made up of many transverse
waves that vibrate in a variety of directions (i.e., in more
than one plane) and is referred to as unpolarized light.
Any arbitrary direction of vibration can be represented as a
combination of a parallel vibration and a perpendicular
vibration
As soon as light interacts with anything, whether through
reflection, transmission, or scattering, there is opportunity
for polarization to be induced.
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Unpolarized light
Unpolarized light can be split into separate polarization
components either by reflection off a nonmetallic surface or
by refraction when the light passes from one material to
another.
The refracted light is polarized depends on the angle at which
the light approaches the surface and on the material itself.
In the case when all the electric field planes of the different
transverse waves are aligned parallel to one another, then
the light wave is linearly polarized. This is the simplest type
of polarization.
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Polarized/unpolarized waves on rope.
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Multitude of
polarization
components
Parallel
polarization
components
Perpendicular
polarization
components
Polarization represented as a combination of a parallel vibration and
perpendicular vibration
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Reflected ray
Incident ray
Ф1
Ф2
n2 < n1
Material interface
n1
Refracted ray
Perpendicular polarization
Parallel polarization
Partially refracted perpendicular polarization
Behavior of an unpolarized light beam at the interface between air and a
nonmetallic surface
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Depending on the orientation of the slot, the train of waves (a) goes entirely
through the slot; (b) is partly reflected and partly transmitted with changed angles
of rope vibration; or (c) is completely reflected.
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Polarization-Sensitive Materials
1. Polarizer
2. Faraday rotator
3. Birefringent crystals
A polarizer is a material or device that transmits only one polarization
component and blocks the other.
A Faraday rotator is a device that rotates the state of polarization
(SOP) of light passing through it by a specific amount
Certain crystalline materials have a property called double refraction
or birefringence. This means that the indices of refraction are slightly
different along two perpendicular axes of the crystal. A device made
from such materials is known as a spatial walk-off polarizer (SWP).
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Polarizer
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Faraday rotator
A Faraday rotator is a device that rotates the state of polarization clockwise
by 45o or a quarter of a wavelength
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Faraday rotator
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Faraday rotator
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Birefringent crystals
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Birefringent crystals
Some Common Birefringent Crystals and Their Ordinary and
Extraordinary Indices of Refraction
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Intentionally Left Blank
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Optical fiber modes and
configurations
Fiber Structures
Cross sections of a generic fiber structure showing a core, a cladding,
and a buffer coating
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Single fiber structure
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Core
1. Light propagates along the core of the fiber.
2. Core material is highly pure silica SiO2 and is
surrounded by glass cladding.
Cladding
1. Cladding reduces scattering loss that results from
the dielectric discontinuities at the core surface.
2. It adds mechanical strength to the fiber
3. It protects the core from absorbing surface
contaminants with which it could come in contact.
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• What does a Micron look like?
Human Hair
.0035 inch
1 Micron
.000039 inch
.001 mm
90 Micron
9 Microns
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Fiber Types
Generally two types
1. Single mode
2. Multimode
Step index Fiber
Graded index Fiber
• Modes
– Simply can be defined as the different paths of the light through
the optical fiber cable
– Every mode is represented by a unique solution of the Maxwell’s
equation inside the core
– The stable Field distribution along the x-axis with only a periodic
z-dependence is known as mode
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Fiber Types
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Fiber Types
Single mode fiber
– Only permits the fundamental mode of the
light
• Smaller diameter of the core
• Numerical aperture is also small
• Reduced acceptance angle
• Difficult to couple the light in the fiber
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Fiber Types
Multimode fiber
– Transmits a large number of modes
– Each mode has the different path through the fiber
– Each mode arrives at the end at slightly different time
(modal dispersion)
– Modal dispersion can be reduced by varying the
refractive index with in the core
– There are two types of multimode fibers
• Step index and graded index
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Fiber Types
• Step index Multimode fiber
– The core of the fiber has the uniform refractive
index.
• Graded index Multimode Fiber

Graded-index fiber becoming very popular for
specialized applications.

It is relatively expensive to manufacture, due
to its complex core structure.
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Fiber Types
Advantages Multimode Fiber:
1. Easier to launch optical power into the fiber.
2. Easier to connect similar optical fibers.
3. LED are used for launching optical power whereas single mode
fiber use Laser.
• LEDs are easier to make
• Less expensive
• Less complex circuitry
• Longer life time
Disadvantage:
1. Intermodal dispersion
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Ray Optics
Ray optics representation of the propagation mechanism in an ideal
step index fiber.
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Ray Optics
• Acceptance angle
– The entering rays which have the angle
greater than θc can be transmitted in
optical fiber
– As the fiber is Circular, so angle is
applicable in two dimensions and would
look like a cone
– The range of incident angles which can
be used for total Internal Reflection is
called Cone of acceptance
–
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Ray Optics
• Numerical Aperture

It is measure of fiber’s light gathering ability.

This represent the coupling of light into the
fiber core.

Think of the aperture as a funnel, the larger
the funnel the more usable light that’s pumped
into the core.
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Ray Optics
• Numerical Aperture

Light will be accepted and propagated only if
it enters the core and strikes the cladding at an
angle greater than the critical angle.

Any light rays striking the core within this
acceptance cone will be propagated down the
fiber.

Sin value of acceptance angle is called
Numerical aperture.
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Ray Optics
Critical angle
Sin θc = n2 / n1
Maximum entrance angle
n sin θ0,max =n1 sin θc = (n12 - n22 ) 1/2
Numerical Aperture NA
NA= n sin θ0,max = (n12 - n22 ) 1/2
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Intentionally Left Blank
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Optical rays transmission through dielectric slab
waveguide
n1  n 2 ;    c 

2
 c
O
For TE-case, when electric waves are normal to the plane of incidence
must be satisfied with following relationship:

2
2
2

 n1 d sin  m   n1 cos   n2
tan 



2  
n1 sin 


Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000




[2-25]
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Note
• Home work 2-1) Find an expression for 
,considering that the electric
field component of optical wave is parallel to the plane of incidence (TMcase).
• As you have seen, the polarization of light wave down the slab waveguide
changes the condition of light transmission. Hence we should also consider
the EM wave analysis of EM wave propagation through the dielectric slab
waveguide. In the next slides, we will introduce the fundamental concepts
of such a treatment, without going into mathematical detail. Basically we
will show the result of solution to the Maxwell’s equations in different
regions of slab waveguide & applying the boundary conditions for electric
& magnetic fields at the surface of each slab. We will try to show the
connection between EM wave and ray optics analyses.
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EM analysis of Slab waveguide
• For each particular angle, in which light ray can be faithfully transmitted
along slab waveguide, we can obtain one possible propagating wave
solution from a Maxwell’s equations or mode.
• The modes with electric field perpendicular to the plane of incidence (page)
are called TE (Transverse Electric) and numbered as: TE 0 , TE 1 , TE 2 ,...
Electric field distribution of these modes for 2D slab waveguide can be
expressed as:

Em ( x, y, z, t )  e x f m ( y) cos(ωt   m z )
[2-26]
m  0,1,2,3 (mode number)
wave transmission along slab waveguides, fibers & other type of optical
waveguides can be fully described by time & z dependency of the mode:
cos(ωt   m z )
or e j (t   m z )
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TE modes in slab waveguide
y
z

Em ( x, y, z, t )  e x f m ( y) cos(ωt   m z )
m  0,1,2,3 (mode number)
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
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Modes in slab waveguide
• The order of the mode is equal to the # of field zeros across the guide. The
order of the mode is also related to the angle in which the ray congruence
corresponding to this mode makes with the plane of the waveguide (or axis
of the fiber). The steeper the angle, the higher the order of the mode.
• For higher order modes the fields are distributed more toward the edges of
the guide and penetrate further into the cladding region.
• Radiation modes in fibers are not trapped in the core & guided by the fiber
but they are still solutions of the Maxwell’ eqs. with the same boundary
conditions. These infinite continuum of the modes results from the optical
power that is outside the fiber acceptance angle being refracted out of the
core.
• In addition to bound & refracted (radiation) modes, there are leaky modes
in optical fiber. They are partially confined to the core & attenuated by
continuously radiating this power out of the core as they traverse along the
fiber (results from Tunneling effect which is quantum mechanical
phenomenon.) A mode remains guided as long as n2 k    n1k
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Optical Fibers: Modal Theory (Guided or
Propagating modes) & Ray Optics Theory
n1
n2
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
n1  n2
Step Index Fiber
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Modal Theory of Step Index fiber
• General expression of EM-wave in the circular fiber can be written as:



E (r ,  , z, t )   Am E m (r ,  , z, t )  AmU m (r ,  )e j ( ωt   m z )
m
m



j ( ωt   m z )
H (r ,  , z, t )   Am H m (r ,  , z, t )   AmVm (r ,  )e
m
m
[2-27]


• Each of the characteristic solutions Em (r ,  , z, t ) & H m (r ,  , z, t ) is
called mth mode of the optical fiber.
• It is often sufficient to give the E-field of the mode.

U m (r,  )e j (ωt   m z )
m  1,2,3...
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
• The modal field distribution, U m (r,  ) , and the mode
propagation constant,  m are obtained from solving the
Maxwell’s equations subject to the boundary conditions given
by the cross sectional dimensions and the dielectric constants
of the fiber.
• Most important characteristics of the EM transmission along the fiber are
determined by the mode propagation constant,  m (ω) , which depends on
the mode & in general varies with frequency or wavelength. This quantity
is always between the plane propagation constant (wave number) of the
core & the cladding media .
n2 k   m (ω)  n1k
[2-28]
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• At each frequency or wavelength, there exists only a finite number of
guided or propagating modes that can carry light energy over a long
distance along the fiber. Each of these modes can propagate in the fiber
only if the frequency is above the cut-off frequency, ω c , (or the source
wavelength is smaller than the cut-off wavelength) obtained from cut-off
condition that is:
 m (ω c )  n 2 k
[2-29]
• To minimize the signal distortion, the fiber is often operated in a single
mode regime. In this regime only the lowest order mode (fundamental
mode) can propagate in the fiber and all higher order modes are under cutoff condition (non-propagating).
• Multi-mode fibers are also extensively used for many applications. In
these fibers many modes carry the optical signal collectively &
simultaneously.
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Fundamental Mode Field Distribution
Mode field diameter
Polarizations of fundamental mode
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
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Different Structures of Optical Fiber
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
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Mode designation in circular cylindrical
waveguide (Optical Fiber)
TE lm modes : The electric field vector lies in transverse plane.
TM lm modes : The magnetic field vector lies in transverse plane.
Hybrid HE lm modes :TE component is larger than TM component.
Hybrid EH lm modes : TM component is larger than TE component.
y
l= # of variation cycles or zeros in direction.
m= # of variation cycles or zeros in r direction.

z
Linearly Polarized (LP) modes in weakly-guided fibers ( n1
r
x
 n2  1 )
LP0 m (HE 1m ), LP1m (TE 0 m  TM 0 m  HE 0 m )
Fundamental Mode:
LP01 (HE 11 )
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Two degenerate fundamental modes in Fibers
(Horizontal & Vertical HE 11 Modes)
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
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Mode propagation constant as a function of frequency
• Mode propagation constant,  lm (ω), is the most important transmission
characteristic of an optical fiber, because the field distribution can be easily
written in the form of eq. [2-27].
• In order to find a mode propagation constant and cut-off frequencies of
various modes of the optical fiber, first we have to calculate the
normalized frequency, V, defined by:
2a
2a
2
2
V
n1  n2 
NA


[2-30]
a: radius of the core,  is the optical free space wavelength,
n1 & n2 are the refractive indices of the core & cladding.
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Plots of the propagation constant as a function of normalized
frequency for a few of the lowest-order modes
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Single mode Operation
• The cut-off wavelength or frequency for each mode is obtained from:
 lm (ω c )  n2 k 
2n2
c

 c n2
[2-31]
c
• Single mode operation is possible (Single mode fiber) when:
V  2.405
[2-32]
Only HE11 can propagate faithfully along optical fiber
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Single-Mode Fibers
  0.1% to 1% ;
a  6 to 12 m ;
V  2.3 to 2.4 @ max frequency or min 
• Example: A fiber with a radius of 4 micrometer and n1  1.500 & n2  1.498
has a normalized frequency of V=2.38 at a wavelength 1 micrometer. The
fiber is single-mode for all wavelengths greater and equal to 1 micrometer.
MFD (Mode Field Diameter): It is an important parameter for single
mode fiber.
• This parameter can be determined from the mode-field distribution of
the fundamental fiber mode.
The electric field of the first fundamental mode can be written as:
E (r )  E 0 exp( 
r2
W0
2
);
MFD  2W0
[2-33]
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Birefringence in single-mode fibers
•
Because of asymmetries the refractive indices for the two degenerate modes
(vertical & horizontal polarizations) are different. This difference is referred to as
birefringence, B f :
B f  n y  nx
Optical Fiber communications, 3rd ed.,G.Keiser,McGrawHill, 2000
[2-34]
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Fiber Beat Length
• In general, a linearly polarized mode is a combination of both of the
degenerate modes. As the modal wave travels along the fiber, the difference
in the refractive indices would change the phase difference between these
two components & thereby the state of the polarization of the mode.
However after certain length referred to as fiber beat length, the modal
wave will produce its original state of polarization. This length is simply
given by:
2
Lp 
kB f
[2-35]
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Multi-Mode Operation
• Total number of modes, M, supported by a multi-mode fiber is
approximately (When V is large) given by:
V2
M 
2
[2-36]
• Power distribution in the core & the cladding: Another quantity of
interest is the ratio of the mode power in the cladding, Pclad to the total
optical power in the fiber, P, which at the wavelengths (or frequencies) far
from the cut-off is given by:
Pclad
4

P
3 M
[2-37]
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Graded Index Fiber (GIN)
• The most commonly used GIN have the index variation of
core as the power law given by


r
n(r )  n1 1  2 
a




1
2
for 0  r  a
n(r )  n1 1  2  2  n1 1     n2 for r  a
1
• No. of bounded modes in GIN fibr is
Mg 

 2
a k n 
2
2
2
1
 V2
 2 2
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The mode field is defined as the distance between the points where the
strength of the electric field is decayed to 0.37 (1/e) of the peak.
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Intentionally Left Blank
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FIBER MATERIALS
In selecting materials following requirements must be satisfied
1.
2.
It must b possible to make long, thin, flexible fibers fro the material
The material must be transparent at a particular wavelength in order for the fiber
to guide light effectively.
3.
Physically compatible materials that have slightly different refractive indices for
the core and cladding must be available
Materials that satisfy these requirements are glasses and plastics
•
Usually fibers are made of glass consisting of either silica SiO2 or silicate
•
•
•
•
Moderate loss fibers with large cores used for short-transmissions
Low loss (very transparent) fibers are used for long-haul applications
Plastics have higher attenuation than the glass fibers
Plastic fibers are used in short distance fibers where more mechanical
stresses are possible
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Glass Fibers
• Glass is made by fusing metal oxide, sulfides or selenides.
• The resulting material is a randomly connected molecular network
called glass.
• Glasses do not have well defined melting points
• Melting point is defined as the temperature at which glass becomes
fluid enough to free itself of glass bubbles.
• The largest category for optical fibers consists of oxide glasses.
• The most common of these oxides is the silica SiO2 which has
refractive index of 1.458 at 850nm
• Fluorine or various oxides such as B2O3, GeO2, or P2O5 can be
doped to slightly change the refractive index for the cladding
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• Plastic material


Plastic fiber has poor optical qualities as compared to glass.
Plastic fibers are more economical over short distances for
slower speeds.
•Midway Solution



Plastic-Clad Silica Fiber.
The above fiber uses a high quality glass core,
with a low cost plastic sheathing.
clad
The cost and performance of plastic-clad Silica fiber is a
compromise between the all-glass and all plastic fibers.
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•
Since the cladding must have
a lower refractive index as
compared to the core so we
can chose the following
options
for the
doped
materials
1.
2.
3.
4.
GeO2 – SiO2, core; SiO2 cladding
P2O5-SiO2, core; SiO2 cladding
SiO2 core; B2O3-SiO2 cladding
GeO-B2O3-SiO2 core; B2O3-SiO2
cladding
•
Here the notation GeO2 – SiO2
denotes a GeO2 doped silica
glass
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Properties of pure silica glass
• Pure silica is referred as silica glass, fused glass
or vitreous silica
• Offer high resistance to deformation at high
temperature as 1000oC
• High resistance to breakage from thermal shock
because of its low thermal expansion
• Good chemical durability
• High transparency in both the visible and infrared region
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ACTIVE GLASS FIBERS
• Incorporating rare earth elements (atomic
numbers 57 - 71) converts normal passive glass
fiber into new materials with new optical and
magnetic properties.
• The new materials perform amplification,
attenuation and phase retardation on the
passing light
• Doping can be carried out for silica, tellurite and
halide glasses
• Commonly used materials are Erbium and
Neodymium
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Plastic Optical Fibers
• High demand for delivering high speed services to the work station
require high bandwidth graded index polymer (plastic) optical fibers
(POF).
• POF’s are used within the premises of user.
• Fiber with core of polymethylmethacrylate referred as (PMMA POF)
• Fiber with core of perfluorinated polymer is referred as PF POF
• POF’s have greater attenuation as compared to glass fibers.
• POF’s are tough and durable as compared to glass fibers
• Modulus is two order of magnitude smaller than the glass fiber so
flexible to install.
• Compared with glass fiber the core diameter is 10 – 20 times larger
• Inexpensive plastic injection moulding technologies can be used to
fabricate connectors, splices and transceivers
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Photonic Crystal Fibers (PCF)
• Demonstrated in 1990, initially called holy fiber and later
called Photonic Crystal Fiber (PCF)
• It has air holes run along the entire length of the fiber
• Sometimes air holes act as cladding known as IndexGuiding PCF
• Another form uses the band gap effect between the core
as air holes and cladding known as photonic band gap
fibers
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Fiber Fabrication
There are two basic techniques for fiber fabrication
• Vapor-phase oxidation process
• Direct melt methods
Direct melt methods :
• Traditional glass making procedure , fibers are made from molten
state of purified silicate glass.
Vapor-phase oxidation process:
• Highly pure vapors of metal halides (SiCl4 and GeCl4) react with
oxygen to form a white powder (SiO2).
• These particles are collected at the surface of the bulk glass by one
of the four processes.
• These rods are then sintered and called preforms.
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•
The preforms are around 10 –
25mm in dia and 60 – 120cm long
•
Fibers are made from this preform
using the fiber drawn equipment
•
Drawing furnace bring it to the
temperature where tip becomes
soft and can be pulled through
take-up drum
•
Thickness depend on the speed of
the drum
•
Finally it is coated with the elastic
material for protection
Fiber Drawing
apparatus
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Outside Vapor-phase oxidation
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Vapor-Phase Axial Deposition (VAD)
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Modified Chemical Vapor Deposition
(MCVD)
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Plasma –Activated Chemical Vapor Deposition
(PCVD)
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Photonic crystal Fibers
Initially this was called holey fiber and later known as photonic
crystal fiber (PCF) or a microstructured fiber.
There are two categories of photonic crystal fibers.
1. Index- Guiding PCF
2. Photonic Bandgap Fiber.
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Natural silicon
dioxide SiO 2
CO
Reduction
Chlorination
Distillation
C,Cl2
FeCl 3
Silicon Tetrachloride
(SiCl4)
H2 ,O2
Cl
2
Quartz and quartz mineral sands
Hydrolysis in the
vapor phase
HCl
O
Fine particle mist
with SiO
Cl2
2
Dry silicon
dioxide SiO
2
Dehydration
Oxidation in the
vapor phase
HCl
Ultrapure silicon
dioxide SiO 2
2
Ultra pure silicon dioxide for use in
fiber manufacture and integrated
circuits
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Vertical preform lathe
Horizontal preform lathe
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Mechanical Properties of Fibers
Two basic mechanical characteristics of glass optical
fibers are:
1. Strength
2. Static fatigue
Strength relates to instantaneous failure under an applied
load.
Static fatigue relates to the slow growth of the pre existing
flaws in the glass fiber under humid conditions and tensile
stress.
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Mechanical Properties of Fibers
Fibers must be able to withstand :
1. Stresses
2. Strains
During
1. Cable manufacturing process
2. Cable installation process
3. In service
Force applied to the fiber can either impulsive or
gradually varying.
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Mechanical Properties of Fibers
Under applied stress:
•Glass will extend elastically up to its breaking strength.
•Metals can be stretched plastically well beyond their true
elastic range
Copper wires can be elongated plastically by more that 20
percent before they fracture.
Glass fibers elongation of only 1 percent are possible before
they fracture occurs.
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Microcrack model
A hypothetical model of a microcrack in an optical fiber
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Mechanical Properties of Fibers
Proof testing:
A high assurance of fiber reliability can be provided by proof
testing.
In this method an optical fiber is subjected to a tensile
load greater than that expected at any time during the
cable manufacturing, installations, and service.
Any fibers that do not pass the proof test are rejected.
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Optical fiber cable
Classification on Cable Structure
Standard
loose buffer tube type
Standard tight
buffer (Bound) type
Fiber Ribbon
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Classification on Cable Structure
Loose buffer tube

The primary coated Fiber is laid loosely in a jelly filled
narrow tube to prevent changes in the fiber’s optical
properties due to
* Pressure
*Tensile stress
* Bends
* Torsion
*Friction
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Classification on Cable Structure
Loose buffer tube

Normally, there are only 4-6 fibers per tube.

The tube must conform to the following requirements.
*
It must not deform through normal
load.
mechanical
*
It must be durable.
*
It must have low friction.
*
It must withstand reasonably rough handling during
installation, without changing the fiber’s optical
properties.
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Classification on Cable Structure
Loose buffer tube
• Area of application

Loose tube fibers have been used very
successfully in all areas of information
transfer.

Used for long distance Networks
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Classification on Cable Structure
Tight Buffered Fibers

The other alternative to protect the primary coated fiber is
achieved by applying a thick layer of plastic directly on the
245-500 m thick primary coated fiber.
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Classification on Cable Structure
Tight Buffered Fibers
Primary coated fiber 245-500 m
Fiber 125  2 m
Color coded layer
900 m
The tight buffer is color-coded according to a standard or
customer’s specification.
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Classification on Cable Structure
Tight Buffered Fibers
• Area of application

Greatest area of application is indoors as connector
cables and rack cables.
Local Area Networks (LAN) use almost exclusively
tight buffered.


Advantages


They are relatively easy to deal with during installation
Easily terminated with a connector.
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Classification on Cable Structure
• Fiber Ribbon Technique

Third relatively new technique for adding buffer is to lay
several (2-12) primary coated fibers next to each other and
then apply the additional coating.

Three methods for ribbon technique:
*
Taping
*
Edge bonding
*
Encapsulating
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Classification on Cable Structure
Fiber Ribbon Technique
• Tapping: initial method
• Edge bounding: filling the Acrylate between
the gapes
• Encapsulation: A layer of Acrylate is
applied around the fibers
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Taping
Edge Bonding
Encapsulation
The three most common methods of manufacturing fiber ribbon.
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Breakout Cable (In door)
Simplex Cord
Duplex figure – 8 / Zip Cord
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Direct Burried Cable
Central strength member
Jelly filled loose tube
PE inner sheath
Corrugated coated steel tape armour
Moisture barrier sheath
PE outer sheath
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Aerial cable.
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Armored outdoor cable
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A typical range of armor protection cable
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Fiber optic underwater cable
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lightweight deep-water cable.
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Cable material

Cable Jackets require a veriety of materials to best
serve the environment to be used in.
These materials offer protection from the following
concerns:
1. Mechanical
2. Chemical
3. Thermal
4. Environmental
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Cable material
1. Polyethylene (PE)

A thermoplastic with good chemical and
moisture resistance.
Application
*
*
Aerial
Direct burried application.
2. Polyurethane (PU)

A polymer with excellent abrasion
resistance and low temperature flexibility.
Application
*
Excellent for duct.
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Cable material

3. Polyvinyl Chloride (PVC)
A thermoplastic with good flame and abrasion resistance.
Application
*
Raceways
*
Duct environments
4.


Teflon.
A fluorocarbon / thermoplastic offers excellent
properties in all cable categories except in radiation
environments.
More costly than other cable material.
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Cable material
Kevlar


An aramid strength member.
It is five times stronger than steel.
Buffer Jacket (Tube)

Protect fiber from moisture, chemicals
and mechanical stresses placed on cable
during installation, and splicing.
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Cable material
Central member


Facilitates stranding
Allows cable flexing
Provides temperature stability

Prevents buckling

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Cable material
Strength member

Primary tensile load bearing member

Aramid Yarns (Kevlar)
Armoring (Burried Cable)

Protection from rodent attack and crushing
forces.

Corrugated steel tape or multiple metal
strands
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