19-03-2011, 04:57 PM
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Introduction to Optical Fibers.
Used to carry signals in the form of light over distances up to 50 km.
Fibers of glass
Usually 120 micrometers in diameter
No repeaters needed.
Core – thin glass center of the fiber where light travels.
Cladding – outer optical material surrounding the core
Buffer Coating – plastic coating that protects the fiber.
Advantages of Optical Fibre
Thinner
Less Expensive
Higher Carrying Capacity
Less Signal Degradation& Digital Signals
Light Signals
Non-Flammable
Light Weight
Type of Fibers
Optical fibers come in two types:
• Single-mode fibers – used to transmit one signal per fiber (used in telephone and cable TV). They have small cores(9 microns in diameter) and transmit infra-red light from laser.
• Multi-mode fibers – used to transmit many signals per fiber (used in computer networks). They have larger cores(62.5 microns in diameter) and transmit infra-red light from LED.
How Does Optical Fibre Transmit Light?
Total Internal Reflection.
When light travelling 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.
How are Optical Fibre’s made?
Three Steps are Involved
-Making a Preform Glass Cylinder
-Drawing the Fibre’s from the preform
-Testing the Fibre
Testing of Optical Fiber
TENSILE STRENGTH TEST
Abrasion Test
CRUNCH TEST (COMPRESSION TEST)
Impact test
REPEATED BENDING TEST
TORSION TEST
WATER PENETRATION TEST
Areas of Application
Telecommunications
Local Area Networks
Cable TV
CCTV
Optical Fiber Sensors