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  • Topic: Optical fiber, Fiber-optic communication, Multi-mode optical fiber
  • Pages : 10 (1263 words )
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  • Published : April 21, 2013
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Optical Communication Concept
R K Gangwar Divisional Engineer(Transmission) BSNL
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Agenda
• History • Why Optical Fiber? • Applications of Optical Fiber

• Transmission Sequence
• Geometry of Fiber

• Principle of Propagation of Light
• Types of Optical Fiber

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History
• • • • 1960: Laser invented 1967: New Communications medium: cladded fiber 1960s: Extremely lossy fiber: more than 1000 dB /km 1970, Corning Glass Work NY, Fiber with loss of less than 2 dB/km 70s & 80s : High quality sources and detectors Late 80s : Loss as low as 0.16 dB/km

• •

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Why Fiber ?
• Many advantages – SPEED: Fiber optic networks operate at high speeds up to the Terabits per seconds – BANDWIDTH: large carrying capacity – Low signal attenuation: Fewer repeaters – RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or other nearby cables. – MAINTENANCE: Fiber optic cables costs much less to maintain – Security

• Extremely difficult to tap a fibre as it does not radiate energy that can be received by a nearby antenna. circulation to Trainees only For

Why Fiber ?
– Security - Being a dielectric • It cannot cause fire. • Does not carry electricity. • Can be run through hazardous areas.

– Low signal attenuation-Fewer repeaters
– Available in Long lengths (> 12 kms)

Less splice points.
– Universal medium Serve all communication needs. Non-obsolescence For circulation to Trainees only

Disadvantages
• • • • •


higher initial cost in installation Interfacing cost Strength: Lower tensile strength Remote electric power more expensive to repair/maintain Tools: Specialized and sophisticated

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APPLICATIONS OF OPTICAL FIBER
1. LONG DISTANCE COMMUNICATION BACKBONES 2. INTER-EXCHANGE JUNCTIONS 3. VIDEO TRANSMISSION 4. BROADBAND SERVICES 5. COMPUTER DATA COMMUNICATION (LAN, WAN etc..) 6. HIGH EMI AREAS 7. FTTH

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Basic fiber optic communication system

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Transmission Sequence
Transmitter
Input Signal Coder or Converter Light Source Source-to-Fiber Interface

Fiber-optic Cable

Fiber-to-light Interface

Light Detector Receiver

Amplifier/Shaper Decoder

Output

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Major elements of an optical fiber link

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Transmission sequence
• Information is encoded into electrical signals. • Electrical signals are converted into light signals. • Light travels down the fibre. • A detector changes the light signals into electrical signals. • Electrical signals are decoded into information

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Electromagnetic spectrum

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Geometry of Fiber

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Geometry of Fiber
• 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.

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Geometry of Fiber Cable

Consist of two concentric layers of high-purity silica glass the core and the cladding The light stays confined to the core because the cladding has a lower refractive index—a measure of its ability to bend light. For circulation to Trainees only

Refraction & Total Internal Reflection

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Principle of Propagation of light

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Principle of Propagation of light
• Light propagates due to

total internal reflection
• Light > critical angle

will be confined to the
core

• Light < critical angle
will be lost in the

cladding
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Types of Fiber
According to Material Used 1. Plastic Fiber 2. Plastic Clad Silica Fiber 3. Glass Fiber According to RI Profile 1. Step Index

2. Graded Index...
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