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
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Glass core glass clad
Doped silica core clad
All plastic fiber
 On the basis of profile
 Step index
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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
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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
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6 to 50 M Hz Km
 Application
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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
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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
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300 to 3 GHz-Km
 Application
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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
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Approx 2 to 5dB/Km @ 0.85 µm wavelength
 Bandwidth
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Greater than 500MHzKm
Theoretically 40GHzKm @ 0.85 µm
Practical bandwidth of 10GHzKM @ 1.3 µm
 Application
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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
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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
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Reduction of micro bending due to environmental conditions
specially temperature
Reduction in hydrogen absorption and nuclear radiation exposure
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