Transmission Characteristics of Optical Fiber
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Transcript Transmission Characteristics of Optical Fiber
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Optical Fiber Classification
Can be classified in a number of ways
On the basis of manufacturing
Single component/Multi component
Glass core glass clad
Doped silica core clad
All plastic fiber
On the basis of profile
Step index
Multi mode
Mono mode
Graded index
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Multi Mode Step Index
Made up of glass or doped silica
Reasonably large core diameter and NA to facilitate
efficient coupling of incoherent light
Performance characteristics vary widely depending upon
material used in fabrication
Structure
Core diameter:
50 to 400 µm
Clad diameter:
125 to 500 µm
Buffer jacket diameter: 250 to 1000 µm
Numerical Aperture:
0.16 to 0.5
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Multi Mode Step Index
Performance characteristics
Attenuation
Approx 2.5 to 50 dB/Km @ 0.85 µm wavelength
40 dB/Km for glass fiber
5 dB/Km for doped silica fiber
0.4 dB/Km @ 1.3 µm wavelength
Bandwidth
6 to 50 M Hz Km
Application
Short haul communication
Limited bandwidth applications
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Relatively low
cost applications
Multi Mode Graded Index
Made up of glass or doped silica
Higher purity level than MMSI fibers
Many different structural profiles developed for different
application
Structure (Typical)
Core diameter:
30 to 100 µm
Clad diameter:
100 to 150 µm
Buffer jacket diameter: 250 to 1000 µm
Numerical Aperture:
0.2 to 0.3
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Multi Mode Graded Index
Structural types
50 /125 µm (core-clad) with NA between 0.20 to 0.24
recommended by ITU-T for telecom applications @ 0.85
and 1.3 µm wavelength. Now mainly used for Data Links
and LANs
65/124 µm (core-clad) with NA between 0.26 to 0.29 for
long distance subscriber loops operating @ 0.85 and 1.3
µm. Now mainly used for LANs
100/125 µm (core-clad)with NA of 0.29. High coupling
efficiency with LEDs operating @ 0.85 µm. Used in low cost,
short distance applications
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Multi Mode Graded Index
Performance characteristics
Attenuation
Approx 2 to 10 dB/Km @ 0.85 µm wavelength
0.4 dB/Km @ 1.3 µm and 0.25dB/Km @1.55 µm
Bandwidth
300 to 3 GHz-Km
Application
Medium haul communication
Medium to high bandwidth applications
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Single Mode Step Index
Made up of doped silica
Small core diameter
Structure
Core diameter:
Clad diameter:
Buffer jacket diameter:
Numerical Aperture:
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5 to 10 µm
Generally 125µm
250 to 1000 µm
0.08 to 0.15 (usually around 0.1)
Single Mode Step Index
Performance characteristics
Attenuation
Approx 2 to 5dB/Km @ 0.85 µm wavelength
Bandwidth
Greater than 500MHzKm
Theoretically 40GHzKm @ 0.85 µm
Practical bandwidth of 10GHzKM @ 1.3 µm
Application
Long haul communication
Excessive bandwidth applications
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Plastic Clad Fibers
Multimode fibers with both step and graded profiles
Glass core and plastic clad (often silicon rubber)
Lower induced radiation losses (improved performance
under certain environments)
Slightly cheaper
Structure
SI
GI
Core diameter:
100 to 500
50 to 100 µm
Clad diameter:
300 to 800
125 to 150 µm
Buffer jacket diameter: 500 to 1000
250 to 1000 µm
Numerical Aperture:
0.2 to 0.3
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0.2 to 0.5
Plastic Clad Fibers
Performance Characteristics
Step Index:
5 to 50 dB/Km
Graded index: 4 to 15 dB/Km
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Optical Fiber Cable
Why we need cabling
Unprotected optical fiber has many disadvantages
Poor strength and stability
Brittle and small cross sections are susceptible to damage
during laying
Hence cabling is done to improve
Fiber protection
Fiber damage and breakage during installation and throughout
life
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Optical Fiber Cable
Cable strength
Should have similar mechanical properties as of electrical cables
Increase in resistance to mechanical stress, strain and adverse
environmental condition
Squeezing and vibrations
Identification of joints
Stability
Reduction of micro bending due to environmental conditions
specially temperature
Reduction in hydrogen absorption and nuclear radiation exposure
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