Optical fibers: fiber parameter, diameter, types

Optical fibers: numerical aperture, fiber parameter, transversal modes, mode field diameter, fiber types

Fiber

Light propagation: inner total reflection




How to change the refractive index?




How much light we can couple into a fiber?




Angle of acceptance: φA

"Opening" angle: 2φA

Numerical aperture: NA= n₀ sin φA


Stepwise (SI) and gradient (GI) index fibers




Transversal modes:

Waves:




Interference in fibers:




Modes:




Fiber parameter:




Single mode operation at V ≤ 2.405

Materials for fibers:

Cladding material	Core material	Fiber type
SiO2 (Glass)	SiO2 (doped) (Glass)	MMF, SMF (GOF)
Polymer	SiO2 (Glass)	MMF (GOF)
Polymer	Polymer	MMF (POF)

Mode field diameter:



Mode field diameter for different fiber parameters
-> in SMF a big part of the field propagates in the cladding!

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