Hello, everyone!
Today, I will explain multimode optical fibers.
There are two types of optical fibers: multimode – MM and singlemode – SM fibers.
Fig. 1. Multimode/Single mode fibers
(https://www.blackbox.co.uk/gb-gb/page/28533/Resources/Technical-Resources/Black-Box-Explains/Fibre-Optic-Cable/Multimode-vs-Singlemode-Fibre)
Multimode fibers have a large core 62.5 or 50 microns, and in these fibers travel many rays (or modes). They are mainly used for indoor installation or outdoor installation for a short distance of up to several kilometers. Multimode fibers are used where there is a problem with dust, because multimode fibers have a bigger core (62.5 or 50 microns) than singlemode fibers (8-10 microns). And equipment for multimode fibers is cheaper.
Figure 2. Multimode and singlemode fibers
(http://www.fiberopticshare.com/single-mode-fiber-vs-multimode-fiber-choose-2.html)
Generally, multimode fibers are used with sources:
LED at wavelengths 850nm and 1300 nm,
VCSEL at wavelength 850nm, and
Fabry-Perot (FP) laser at wavelength 1300 nm.
There are:
step index multimode fibers and
graded index multimode fibers.
There are special multimode fibers:
Plastic Optical Fiber – POF, this optical fiber has the biggest core, it is about 1mm. POF is step index multimode fiber, and we can use these fibers in very short and low speed networks.
Plastic Clad Silica – PCS/Hard Clad Silica – HCS, these multimode fibers have plastic cladding and glass core. PCS/HCS has a core of about 200 microns, and we can use these fibers in short and low speed networks. PCS/HCS fibers are step index multimode fibers.
These special multimode optical fibers are mainly used for users audio and television links.
Generally, we have used graded index multimode fibers in many applications – premises networks, LANs, security systems, etc. These fibers have bigger bandwidth than step index multimode fibers. There are fibers with core 62.5 or 50 microns and there are five types of these fibers:
OM1 (62.5/125 microns),
OM2 (50/125 microns),
OM3 (50/125 microns),
OM4 (50/125 microns) and
OM5 (50/125 microns).
Detailed parameters for these fibers, we can see in the next table:
Table 1. Transmission performance parameters
(https://www.blackbox.co.uk/gb-gb/page/28533/Resources/Technical-Resources/Black-Box-Explains/Fibre-Optic-Cable/Multimode-vs-Singlemode-Fibre)
On the next picture, we can see multimode fiber jacket color codes.
Fig. 3. Multimode fiber jacket color codes
(https://cleerlinefiber.com/2021/01/27/multimode-fiber-types/)
Thank you!
