| Tero,
Well, I'll try to provide a basic answer.
Multimode optical fibers support many optical modes. Single-mode
optical fibers support a single optical mode. By 'support', I mean
'allow to propagate through the fiber' to the far end.
All fibers have two distinct regions of different refractive index.
The core material of high refractive index is surrounded by a region
of cladding material of lower refractive index. The diameter of
the core for multimode fibers types include 50, 62.5 and 100 microns
for the glass optical fibers that we usually use for high speed
data and telecom systems. Most of the clad diameters are 125 micron,
except for the 100 micron core fiber which has a 140 micron
diameter cladding.
Single-mode optical fibers have core diameters in the range of 8 to
10 microns, with 125 micron clad diameter.
Multimode fibers are generally used with LED (Light Emitting Diode)
sources. System links are generally limited to ~2 kilometers.
Single-mode fibers virtually always require use of lasers as
sources, because of the small core size. Single-mode systems
can run over greater distances than MMF - up to 60 kilometers
is feasible.
Multimode transmitter/receivers sell for ~$60 for FDDI speed
devices. Single-mode devices go for ~$500.
As a starter on the web, try:
http://www.usa.net/corning-fiber/
http://ofl.phys.polymtl.ca/Fibers_html/Fibers.html
and you might look at a news group:
sci.optics.fiber
Regards,
Dick Kirk
|