Fiber Optics Unit 3
Fiber Optics Unit 3
Fiber Optics Unit 3
Internet Access
Glass Cladding
Low Attenuation
High Attenuation
Affordable
Very Durable
How Does Optical Fibre Transmit Light??
Total Internal Reflection.
Fibre Optics Relay Systems has
-Transmitter
-Optical Fibre
-Optical Regenerator
-Optical Receiver
Optical fibre cable
A bundle of optical fibres consists of thousands of
individual fibre wires as thin as human hair,
measuring 0.004 mm in diameter is known as optical
fibre cable.
Total Internal Reflection in Fiber
Total Internal Reflection in Fiber
The optical fibre obeys the laws of reflection and
refraction of light waves.
The reflection or refraction of
the light at the interface depends
on the difference in the speed of
light in two materials having
different refractive indices and
angle of incidence.
Case 1. (Green color)
The refracted ray bends away from normal because the
refractive index n1 of the first medium is grater than
the refractive index n2 of second medium (n1 > n2).
If the angle made by the refracted ray with normal is θ2,
then θ2 > θ1.
Glass Plastic
fibre fibre Step Graded
index index
Single Multi fibre fibre
mode mode
fibre fibre
Fiber optic materials
They are of two types
Glass fibers
Plastic fibers
Glass
fibers
These are made up of fused mixtures of metal oxides and
silica glasses.
The most common is silica with a refractive index of 1.458 at
850 nm.
To Produce two similar materials having slightly different
indices of refraction for the core and cladding, either fluorine
or various oxides such as Boron Oxide, Germanium oxide, or
P2O5 are added to silica.
Examples:
1. GeO2 – SiO2 core; SiO2 Cladding
2. P2O5 – SiO2 Core; SiO2 Cladding
3. SiO2Core; P2O5 – SiO2 Cladding
Glass fibers
Core Cladding
GeO2-SiO2 SiO2
P2O5-SiO2 SiO2
SiO2 P2O5-SiO2
Another type of silica glasses are the low melting silicates. Such optical fibre are
made of soda-lime silicates, germanosilicates and varioius borosilicates
Plastic Fibers
They are made up of plastic. Low in cost.
Greater signal attenuation than glass fibers.
Has toughness and durability.
Numerical aperture 0.58 (high)
Acceptance angle up to 70⁰.
Plastic Fibers
Core n1 Cladding n2
1. Source
2. Detectors
3. Connectors
4. Couplers
5. Receptor and
6. Multipliers
1. Source
2. Detectors
3. Connectors
4. Couplers
5. Receptor and
6. Multipliers
Source: Active component in OCS (Optical Communication System)
Used to convert the electrical energy into optical energy in an
efficient manner and resulting in successful launching of light into
the optical fibre.
Characteristics of light Source:
1. Continuously at room temperature
2. Light output should be modulated over a wide range of
frequencies
3. The wavelength of the output should coincide with one of the
transmission window
4. To couple large amount of power into the fibre and the output
spectrum should be small to reduce material dispersion
Two Catagories:
1. Fusion Splicing
The two fibre ends are viewed through microscope and placed together using
micropositioners
After aligning the two ends at correct position, an electric arc is struck across
the joint causing two ends to melt and fuse.
2. Ferrule-type Connector
Precision made ferrule to accurately align the fibre core and hence the two fibre
is joined together.
Coupler: