Download - TTQ 2-2 Light Propagation
Content
• Geometrical optics
• Optical propagation in fiber
• Fiber fabrication
• Signal degradation in fiber• Signal degradation in fiber
• Types of fiber
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Basic parameters
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Light: an electro-magnetic (EM) wave and
discrete energy packets (photon)
• Different power distribution. Why?
– Video: multi mode fiber
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Johann Carl Friedrich Gauss
Michael Faraday André-Marie Ampère
James Clerk Maxwell
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• Very low loss and axial circular symmetry of fiber give
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• Ez inside the core:
Bessel function
• Ez outside the core:
modified Bessel
function
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Optical propagation in fiber
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Fiber mode
• There are several modes when light propagates in fiber
– Transverse electric (TE) mode: EZ=0
– Transverse magnetic (TM) mode: HZ=0– Transverse magnetic (TM) mode: HZ=0
– Hybrid mode: EZ≠0 and HZ≠0
• Hybrid mode is denoted HE or EH depending on whether HZ or EZ is larger
– For each l, Bessel’s functions have m roots, so each mode is denote as MODElm (TE01, TM01, HE11
etc.)
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The number of modes
depends on
• The value of V for a mode to appear is its “cut-off frequency”11
Conclusion
• Electromagnetic field distributes in several modes.
• The field are not confined to the core, high order
modes penetrate further into the cladding
• TE and TM modes only appear when l=0, all other • TE and TM modes only appear when l=0, all other
modes are hybrid modes.
• There is always at least one mode (HE11)
• More modes appear as V increases
• The value V=2.405 is the condition for one mode or
multi-mode
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Examples for chapter 2.2
• Problems 2-19:
– Determine the normalized frequency (V) at 820
nm for a step index fiber having a 25-μm core
radius, n1=1.48 and n2=1.46 radius, n1=1.48 and n2=1.46
Content
• Geometrical optics
• Optical propagation in fiber
• Fiber fabrication
• Signal degradation in fiber• Signal degradation in fiber
• Types of fiber
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Fiber fabrication
• Refer to section 2.8 in text book [1]
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Fiber fabrication
• Video.
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