Transcript Slide 1

GLASS
• Glass- not just a functional material to let
light into an area
• Used to add decorative effect.
• Important to choose the right kind of glass
for the right place- to be effective,
attractive and safe.
• The wrong type of glass used in the wrong
position can be unsatisfactory and present
a serious hazard to personnel safety.
Different types of glass
1. 'Ordinary' sheet glass
2. Float glass (plate)
3. Energy efficient glass
4. Patterned (obscured glass)
5. Toughened (Safety glass)
6. Laminated glass
7. Wired glass
8. Mirrors
9. Picture frame glass
10. Soda-lime glass (or lime glass)
11. Lead-alkali glass (also called lead glass)
12. Borosilicate glass
13. Alumino-silicate glass
14. Ninety-six percent silica glass
15. Fused silica glass
16. Fused Quartz
17. Colouring Glass
1. 'Ordinary' sheet glass
• This glass is made by passing the molten glass through
rollers; this process gives an almost flat finish but the
effects of the rollers upon the molten glass makes some
distortion inevitable. The glass can be used in domestic
windows etc. but the relatively low cost of float glass
(with its lack of distortion) has tended to restrict ordinary
sheet glass to glazing greenhouses and garden sheds
where the visual distortions do not matter.
• Sheet glass can be cut a glass cutter and no special
equipment is necessary. The glass is often available in
standard sizes to suit 'standard' glasshouses, these
sizes tend to be comparatively cheaper than glass cut to
size.
2. Float glass (plate)
• Float glass gets its name from the method of
production used to manufacture it. The molten
glass is 'floated' onto a bed of molten tin - this
produces a glass which is flat and distortion free.
• Float glass can be cut using a glass cutter and
no special equipment is necessary. Float glass is
suitable for fixed and opening windows above
waist height.
3. Energy efficient glass
• Some manufacturers produce float glass with a special
thin coating on one side which, allows the suns energy to
pass through in one direction while reducing the thermal
transfer the other way. The principle behind this is the
difference in thermal wavelength of energy transmitted
from the sun and that transmitted from the heat within a
room.
• The special coating often gives a very slight brown or
grey tint to the glass. The coating is not very robust and
would not last very long if subjected to normal cleaning
or external weather conditions - for these reasons, this
type of glass is normally only used in sealed double (or
triple) glazed units with the special coating on the inside
4. Patterned (obscured glass)
• Made from flat glass, this type has a design rolled onto
one side during manufacture. It can be used for
decorative effect and/or to provide privacy. Patterned
glass is available in a range of coloured tints as well as
plain.
• A variety of pattern designs are available, each pattern
normally has an quoted distortion number, from 1 to 5, 1
being very little distortion, 5 being a high level of
diffusion.
• On external glazing, the patterned side is usually on the
inside so that atmospheric dirt can easily be removed
from the relatively flat external face.
5. Toughened (Safety glass)
• Toughened glass is produced by applying a special treatment to
ordinary float glass after it has been cut to size and finished. The
treatment involves heating the glass so that it begins to soften
(about 620 degrees C) and then rapidly cooling it. This produces a
glass which, if broken, breaks into small pieces without sharp edges.
The treatment does increase the surface tension of the glass which
can cause it to 'explode' if broken; this is more a dramatic effect than
hazardous.
• It is important to note that the treatment must be applied only after
all cutting and processing has been completed, as once 'toughened',
any attempt to cut the glass will cause it to shatter.
• Toughened glass is ideal for glazed doors, low level windows (for
safety) and for tabletops (where it can withstand high temperature
associated with cooking pots etc.
6. Laminated glass
• As the name suggests, laminated glass is made up of a
sandwich of two or more sheets of glass (or plastic),
bonded together by a flexible, normally transparent
material.
• If the glass is cracked or broken, the flexible material is
designed to hold the glass fragments in place.
• The glass used can be any of the other basic types
(float, toughened, wired etc.) and they retain their
original breaking properties.
• Some laminated glass is laminated for other reasons
than just keeping any broken glass in place, some
provide decorative internal finishes to the glass while
others act as fire breaks.
7. Wired glass
• Wired glass incorporates a wire mesh (usually
about 10mm spacing) in the middle of the glass.
Should be glass crack or break, the wire tends to
hold the glass together. It is ideal for roofing in
such areas as a garage or conservatory where
its 'industrial' look is not too unattractive.
• Wired glass is generally not considered a Safety
glass as the glass still breaks with sharp edges.
• Wired glass is available as clear or obscured.
8. Mirrors
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• Mirrors are usually made from float glass 4-6mm
thick, and silvered on one side. Mirrors are
available for use without a surrounding frame,
these usually are made from a type of safety
glass. Old mirrors, and modern mirrors supplied
within a frame, should not be used unframed as
any damage to them might cause the glass to
shatter dangerously.
9. Picture frame glass
• Glass (and plastics) are available specifically for
picture framing, these tend to be referred to as
'diffused reflection' glass or plastic. They have
high transparency but low reflective properties to
reduce reflections when the picture or
photograph is viewed.
• Most of these materials can easily be cut by the
average diy person providing suitable tools and
safety precautions are taken.
10. Soda-lime glass
( lime glass)
most common glass. •
It is made of oxides of
silicon (SiO2), calcium
(CaO) and
sodium(Na2O).
cheap to make and
can be made into a •
wide variety of shapes;
medium resistance to
high temperatures and
sudden changes of
temperature, fair
resistance to corrosive •
chemicals.
used to make
bottles and windows
With only minor
compositional differences
designed to optimize the
glass for the forming
process and application.
Soda lime glass is used as
the outer shell for both
incandescent and
fluorescent lighting
applications.
Also used in non-lighting
applications such as
Christmas Glass
11. Lead-alkali glass
(also called lead glass)
• lead oxide (PbO) is used in place of
calcium oxide.
more expensive than soda-lime glass;
excellent electrical insulating properties;
poor resistance to high temperatures and
sudden changes of temperature.
used for electrical applications.
• . Lead Glass
• Lead glass is melted and drawn into smalldiameter tubing at the Versailles, KY plant.
This glass has a much higher electrical
resistivity and remains workable over a
wider temperature range than soda lime
glass. Its primary use is for flare and
exhaust tubing in incandescent and
fluorescent lighting products. It also is used
extensively for neon signs.
12. Borosilicate glass
• appreciable resistance to high
temperature or sudden changes in
temperature; medium resistance to
chemical attack. Moderate cost to make.
used for light bulbs, photochromic
glasses, sealed-beam headlights,
laboratory ware, and some bake ware
products.
Borosilicate Glass
Borosilicate glass is melted and formed
into blown bulbs and small diameter
tubing at our Central Falls, RI, facility.
This glass has high durability, high
thermal shock resistance, and high
electrical resistivity. Its optical
transmission is controlled to cut off
harmful ultraviolet radiation. Borosilicate
glass is designed for HID (high-intensity
discharge) lighting applications, in which
hot lamps are exposed to outdoor
conditions for many years.
The tubing drawn from this glass seals
well to both the tungsten lead wires and
the blown bulbs, and therefore is used
for flare and exhaust tubing in HID
applications.
13. Alumino-silicate glass
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alumina (Al2O3) is added to the glass
batch to improve the properties of the
glass.
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good resistance to high temperature or
sudden changes in temperature; difficult
to make.
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used in electronics
14. Ninety-six percent silica glass
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special type of glass
made by a proprietary
method, at temperatures
up to 900°C.
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used to furnace sight
glasses, for outer
windows on space
vehicles.
15. Fused silica glass
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only made of silicon dioxide (SiO2) in
the noncrystalline state.
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expensive and difficult to make;
maximum resistance to high temperature
(900°C for extended periods, 1200°C for
short periods).
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used in special applications such as
optical waveguides, crucibles
16. Fused Quartz
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Fused Quartz are ultra pure, single component glasses (SiO2) with a unique
combination of thermal, optical and mechanical properties, which make
them the preferred materials for use in a variety of processes and
applications where other materials are not suitable.
The very high purity (over 99.9% ) ensures minimum contamination in
process applications.
These materials can routinely withstand temperatures of over 1250ºC, and
due to their very low coefficient of thermal expansion can be rapidly heated
and cooled with virtually no risk of breakage due to thermal shock.
Fused Quartz are inert to most substances, including virtually all acids,
allowing their use in arduous and hostile environments.
The dielectric properties and very high electrical receptivity of these
materials over a wide range of temperatures, together with their low thermal
conductivity allow their use as an electrical and thermal insulating material
in a range of environments.
Fused Quartz is manufactured using powdered quartz crystal as a
feedstock and is normally transparent; the fusion process is carried out at
high temperature (over 2000ºC).
Fused Quartz
Fused quartz products are melted and formed
at our Exeter facility. Major applications include
both the lighting and semiconductor industry.
In lighting products, fused quartz is widely
used in high-temperature arc and filament
lamps requiring high purity to minimize
devitrification and provide optimum sag
resistance. These attributes contribute to the
long life of these lamps at high operating
temperatures.
Major semiconductor manufacturers
worldwide use OSRAM SYLVANIA's fused
quartz for its high chemical purity, hightemperature resistance, and precise
dimensional tolerances. Common applications
include furnace tubes for oxidation, CVD and
diffusion processes, end caps, transfer
carriers, thermocouple tubes, wafer carriers,
end plates, baffles and bell-jars for epitaxial
reactors.
Fused quartz and fused silica
• Vitreous silica is the generic term used to describe all
types of silica glass, with producers referring to the
material as either fused quartz or as fused silica.
• originally used to distinguish between transparent and
opaque grades of the material.
• Fused quartz products - those produced from quartz
crystal into transparent ware, and fused silica manufactured from sand into opaque ware.
• Advances in raw material bonification permit transparent
fusions from sand as well as from crystal.
• Consequently, if naturally occurring crystalline silica
(sand or rock) is melted, the material is simply called
fused quartz.
• If the silicon dioxide is synthetically derived the material
is referred to as synthetic fused silica.
• Controlled Process: The performance of most
fused quartz products is closely related to the
purity of the material. The proprietary raw
material bonification and fusion processes are
closely monitored and controlled to yield
typically less than 50 ppm total elemental
impurities by weight. Clear fused quartz varieties
have a nominal purity of 99.995 W % SiO2.
Structural hydroxyl (OH-) impurities are also
shown. The strong IR absorption of OH- species
in fused quartz provides a quantitative method
for analysis. Beta Factor: The term Beta Factor
is often used to characterize the hydroxyl (OH-)
content of fused quartz tubing. This term is
defined by the formula shown below.
Property
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Typical Values
Density
2.2x103 kg/mm3
Hardness
5.5 - 6.5 Mohs' Scale 570 KHN 100
Design Tensile Strength
4.8x107 Pa (N/mm2) (7000 psi)
Design Compressive Strength Greater than 1.1 x l09 Pa (160,000 psi)
Bulk Modulus
3.7x1010 Pa (5.3x106 psi)
Rigidity Modulus
3.1x1010 Pa (4.5x106 psi)
Young's Modulus
7.2x10-10 Pa (10.5x106 psi)
Poisson's Ratio
.17
Coefficient of Thermal Expansion 5.5x10 -7 cm/cm . oC (20øC-320oC)
Thermal Conductivity
1.4 W/m . oC
Specific Heat
670 J/kg . oC
Softening Point
1683oC
Annealing Point
1215oC
Strain Point
1120 oC
Electrical Receptivity
7x107 ohm cm (350oC)
Dielectric Properties
(20oC and 1 MHz)
Constant
3.75
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Strength
5x107 V/m
Loss Factor
Less than 4x10 -4
Dissipation Factor
Less than 1x10 -4
Index of Refraction
1.4585
Contingence (Nu)
67.56
Velocity of Sound-Shear Wave
3.75x103 m/s
Velocity of Sound/Compression Wave 5.90x103 m/s
Sonic Attenuation
Less than 11 db/m MHz
Permeability Constants (cm3 mm/cm2 sec cm of Hg)
(700oC)
Helium
210x10 -10
Hydrogen
21x10 -10
Deuterium
17x10 -10
Neon
9.5x10 -17
• Electrical Properties
Electrical conductivity in fused quartz is ionic in
nature.
Alkali ions exist only as trace constituents.
Fused quartz is preferred for electrical insulation
and low loss dielectric properties.
The electrical insulating properties of clear fused
quartz are superior to those of the opaque or
translucent types.
Both electrical insulation and microwave
transmission properties are retained at very high
temperatures and over a wide range of
frequencies.
• Effects Of Temperature
Fused quartz is a solid material at room
temperature, but at high temperatures,
it behaves like all glasses.
It does not experience a distinct melting
point as crystalline materials do, but
softens over a fairly broad temperature
range.
This transition from a solid to a plasticlike behavior, called the transformation
range, is distinguished by a continuous
change in viscosity with temperature.
• Viscosity
• Viscosity- the measure of the resistance to flow.
• viscosity scale is generally expressed
logarithmically.
• Common glass terms for expressing viscosity
include: strain point, annealing point, and softening
point, which are defined as: Strain Point: The
temperature at which the internal stress is
substantially relieved in four hours. This
corresponds to a viscosity of 10 14.5 poise, where
poise = dynes/cm2 sec.
• Annealing Point: The temperature at which the
internal stress is substantially relieved in 15
minutes, a viscosity of 10 13.2 poise.
• Softening Point: The temperature at which glass will
deform under its own weight, a viscosity of
approximately 10 7.6 poise. The softening point of
fused quartz has been variously reported from 1500
ºC to 1670ºC, the range resulting from differing
conditions of measurement.
• Cristobalite Growth
The growth rate of cristobalite from the nucleation site
depends on certain environmental factors and material
characteristics.
Temperature and quartz viscosity are the most significant
factors, but oxygen and water vapor partial pressures
also impact the crystal growth rate.
Consequently, the rate of devitrification of fused quartz
increases with increasing hydroxyl (OH-) content,
decreasing viscosity and increasing temperature.
High viscosity, low hydroxyl fused quartz materials
produced , therefore, provide an advantage in
devitrification resistance.
The phase transformation to Beta-cristobalite generally
does not occur below 1000ºC. This transformation can be
detrimental to the structural integrity of fused quartz if it
is thermally cycled through the crystallographic
inversion temperature range (250 ºC). This inversion is
accompanied by a large change in density and can result
in spalling and possible mechanical failure.
• Mechanical Properties
• Mechanical properties of fused quartz are much
the same as those of other glasses. Material is
extremely strong in compression, with design
compressive strength of better than 1.1 x 10 9
Pa (160,000 psi).
• Surface flaws can drastically reduce the inherent
strength of any glass, so tensile properties are
greatly influenced by these defects. The design
tensile strength for fused quartz with good
surface quality is in excess of 4.8 x 10 7 Pa
(7,000 psi). In practice, a design stress of .68 x
10 7 Pa (1,000 psi) is generally recommended.
• Thermal Properties
• One of the most important properties of fused quartz is
its extremely low coefficient of expansion: 5.5 x 10 -7
mm ºC (20-320ºC). Its coefficient is 1/34 that of copper
and only 1/7 of borosilicate glass. This makes the
material particularly useful for optical flats, mirrors,
furnace windows and critical optical applications which
require minimum sensitivity to thermal changes. A
related property is its unusually high thermal shock
resistance.
• For example, thin sections can be heated rapidly to
above 1500 ºC and then plunged into water without
cracking. The residual stress or design, depending on
the application, may be in the range of 1.7 x 10 7 to 20.4
x 10 7 Pa (25 to 300 psi). As a general rule, it is possible
to cool up to 100ºC /hour for sections less than 25 mm
thick.
• Optical Properties
• Optical transmission properties provide a means for
distinguishing among various types of vitreous silica as
the degree of transparency reflects material purity and
the method of manufacture.
• Specific indicators are the UV cutoff and the presence or
absence of bands at 245 nm and 2.73 um. The UV cutoff
ranges from ~155 to 175 nm for a 10 mm thick specimen
and for pure fused quartz is a reflection of material purity.
• The presence of transition metallic impurities will shift the
cutoff toward longer wavelengths. When desired,
intentional doping, e.g., with Ti in the case of Type 219,
may be employed to increase absorption in the UV.
• The absorption band at 245 nm characterizes a reduced
glass and typifies material made by electric fusion. If a
vitreous silica is formed by a "wet" process, either flame
fusion or synthetic material, for example, the
fundamental vibrational band of incorporated structural
hydroxyl ions will absorb strongly at 2.73 um.
17. Colouring Glass
• Unless the raw materials are very pure, glass is
normally green.
• In order to change the colour of glass, one can
decolourise the glass by adding colorants which
produce the complementary colour to green.
• The colour depends on the state of oxidation of
the colorant, the composition of the glass and
the thermal treatment.
COLORANT
GLASS COLOUR/S
iron
green and aqua
iron and sulfur
amber
copper
light blue
cobalt
dark blue
manganese
Purple
tin and calcium
opaque white
lead plus antimony
opaque yellow
selenium
red
neodymium
purple
praseodymium
green
cerium
yellow
carbon and sulphur amber, brown
cadmium sulphide
yellow
antimony sulphide
red
gold
red
Strength of Glass
• Glass is a strong material. Like most
materials, glass can be bent until a certain
limit.
Imagine bending a long rod of glass. If you
release the tension before this limit, the
rod returns to its original shape. The
deformation is elastic. If you pass the
limit, the glass breaks
Why does glass shatter?
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The strength of glass is only slightly affected by
composition but is highly dependent on the
surface condition. If stress is applied on the
damaged surface, the stress at the damaged
points will be increased and the glass will
shatter.
• Glass does not age quickly: glass windows
remain clear and undamaged after many years
of exposure to the elements.
Properties of Glass
• The thermal, optical, electrical and chemical properties of glass
vary with its composition.
• Glass is a good thermal conductor.
• Glass is an electrically insulating material: it does not conduct
electricity.
• When light falls on glass, part of the light is reflected at the surface,
part of the light is absorbed in the glass, and part of the light is
transmitted.
• If most of the light is transmitted, the glass is transparent. By
colouring the glass or changing its composition, it is possible to
transmit selectively some wavelengths of the spectrum.
• Common glass does not transmit ultra-violet radiation (short
wavelengths): you will not get a tan behind a window!
However it does transmit infrared radiation
Some Chemical Properties of Glass
• The chemical properties of glass vary with its
composition.
• Glass is highly resistant to most chemicals: this
is why it is in use in all chemistry labs. Its big
enemy is hydrofluoric acid which dissolves
glass quickly.
• Water can corrode glass at very high
temperatures, especially if the water is alkaline
(Ph > 7). At low temperatures however, water
corrosion is very
Light and Glass
• Scientists and engineers have experimented with light and ways to
guide light for many centuries: glass was the prime choice material.
• It was not until the 1950's that the first optical fibres were made.
Although these optical fibres could transmit light, they did not carry
information very far: most of the signal was lost due to a high
absorption.
• In 1966, Dr. C.K. Kao and George A. Hockham published a paper
in which they discussed and proved the possibility of long distance
communications over optical fibres provided that the optical fibres
had low absorption.
• In 1970, three Corning scientists Dr Robert Maurer, Dr Donald
Keck and Dr Peter Schultz developed the first low absorption
optical fibre.
• Just a dream more than 3 decades ago, long distance
communication through optical fibres has now become a reality.
Glass at the Atomic Scale
• Glass holds a special place in physics: it is not a crystalline solid
and it is not a liquid.
• A crystal is made of atoms which are arranged in a unit cell. This
unit cell is repeated in all three directions. This order is retained over
long atomic distances: it is referred to as long range order.
• A liquid on the other hand lacks this order: the atoms are not rigidly
bound to each other and they "flow" in the material. A liquid has no
order.
• Glass is an amorphous or non-crystalline solid: it is in a state
between the crystalline state and the liquid state. It does not have
the long range order of crystals but it is not a liquid either. The atoms
in the glass are bound to each other but they lack the long range
order. However locally they can be ordered and possess a short
range order.
OPTICAL FIBRE
• Made of extremely pure silica.
• Thinner than a human hair and stronger than
a steel fibre of similar thickness. It can carry
thousands of times more information than a
copper wire!
• Optical fibre cables have the advantage of
being lighter and taking less space than
copper wire cables for the same information
capacity.
Fabrication of Optical Fibres
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The best cakes are made of the best ingredients.
To make a good optical fibre, we need to start with good quality materials,
that is highly purified materials.
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The presence of impurities alter the optical properties of the fibre.
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There are several ways to manufacture optical fibres:
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Directly drawing the fibre from what is called a preform.
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The fibre is
then drawn from the preform
i) Direct Techniques
Two methods can be used to draw a fibre directly:
1. Double Crucible method
2. Rod in Tube method
1. Double Crucible
The molten core glass is placed in the
inner crucible.
The molten cladding glass is placed in
the outer crucible.
The two glasses come together at the
base of the outer cucible and a fibre is
drawn.
Long fibres can be produced (providing
you don't let the content of the crucibles
run dry!).
Step-index fibres and graded-index
fibres can be drawn with this method.
2. Rod in Tube
A rod of core glass is placed
inside a tube of cladding glass.
The end of this assembly is
heated; both are softened and a
fibre is drawn.
Rod and tube are usually 1 m
long. The core rod has typically
a 30 mm diameter. The core
glass and the cladding glass
must have similar softening
temperatures.
This method is relatively easy:
just need to purchase the rod
and the tube.
However, must be very careful
not to introduce impurities
between the core and the
cladding.
ii) Deposition Techniques
• Most optical fibres are made from preforms. The
preforms are made by deposition of silica and various
dopants from mixing certain chemicals; the fibre is then
drawn from the preform.
• Many techniques are used to make preforms. Among
them:
• · Modified Chemical Vapour Deposition or MCVD
• · Plasma-Enhanced Modified Chemical Vapour
Deposition or PMCVD
• · Outside Vapour Deposition or OVD
• · Axial Vapour Deposition or AVD
The Chemicals
• Oxygen (O2) and silicon tetrachloride
(SiCl4) react to make silica (SiO2).
• Pure silica is doped with other chemicals
such as boron oxide (B2O3), germanium
dioxide (GeO2) and phosphorus
pentoxide (P2O5) are used to change the
refractive index of the glass.
Modified Chemical Vapour
Deposition (MCVD)
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The chemicals are mixed inside a
glass tube that is rotating on a lathe.
They react and extremely fine
particles of germano or phosphoro
silicate glass are deposited on the
inside of the tube.
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A travelling burner moving along the
tube:
causes a reaction to take place and
then fuses the deposited material.
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The preform is deposited layer by
layer starting first with the cladding
layers and followed by the core
layers.
Varying the mixture of chemicals
changes the refractive index of the
glass.
When the deposition is complete, the
tube is collapsed at 2000 C into a
preform of the purest silica with a core
of different composition.
The preform is then put into a furnace
for drawing.
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Plasma-Enhanced Modified Chemical
Vapour Deposition (PMCVD)
Plasma-Enhanced Modified
Chemical Vapour Deposition is
similar in principle to MCVD. The
difference lies in the use of a
plasma instead of a torch.
The plasma is a region of
electrically heated ionised gases.
It provides sufficient heat to
increase the chemical reaction
rates inside the tube and the
deposition rate.
This technique can be used to
manufacture very long fibres (50
km).
It is used for both step index and
graded index fibres.
Outside Vapour Deposition (OVD)
The chemical vapours
are oxidised in a flame in
a process called
hydrolysis.
The deposition is done
on the outside of a silica
rod as the torch moves
laterally.
When the deposition is
complete, the rod is
removed and the
resulting tube is thermally
collapsed
Axial Vapour Deposition (AVD)
The deposition occurs on
the end of a rotating
silica boule as chemical
vapors react to form silica.
Core preforms and very
long fibres can be made
with this technique.
Step-index fibres and
graded-index fibres can
be manufactured this w
From Preform to Fibre
• All these deposition
techniques produce
preforms. These
are typically 1 m
long and have a 2
cm diameter but
these dimensions
vary with the
manufacturer.
• The preform is one
step away from the
thin optical fibre.
This step involves a
process called
drawing.
Fibre Drawing and Spooling
• During this last step
of the fabrication
process, many things
will happen to the
fibre:
• · the fibre is drawn
from the preform.
• · it is quality
checked
• · it is coated for
protection
• · it is stored on a
spool (just like a
photographic film).
• The tip of the preform is heated to about
2000°C in a furnace.
As the glass softens, a thin strand of softened
glass falls by gravity and cools down.
• As the fibre is drawn its diameter is constantly
monitored
• A plastic coating is then applied to the fibre,
before it touches any components. The coating
protects the fibre from dust and moisture.
• The fibre is then wrapped around a spool.
Fabrication of an Optical Fibre
Heating the preform
Drawing the fibre