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Fluorescents
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LEDs
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Magic
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Lasers
EXPLANATION
According to Wiki.
Multi-mode fibers are described by their core and
cladding
diameters. Thus, 62.5/125 µm multi-mode fiber has a core size of 62.5
micrometres (µm) and a cladding diameter of 125 µm. The transition
between the core and cladding can be sharp, which is called a
step-index profile, or a gradual transition, which is called a
graded-index profile. The two types have different dispersion characteristics and thus different effective propagation distance.
[6] Multi-mode fibers may be constructed with either
graded or
step-index profile.
[7]
In addition, multi-mode fibers are described using a system of classification determined by the
ISO 11801 standard — OM1, OM2, and OM3 — which is based on the
modal bandwidth of the multi-mode fiber. OM4 (defined in TIA-492-AAAD) was finalized in August 2009,
[8] and was published by the end of 2009 by the
TIA.
[9] OM4 cable will support 125m links at 40 and 100 Gbit/s. The letters "OM" stand for
optical multi-mode.
For many years 62.5/125 µm (OM1) and conventional 50/125 µm
multi-mode fiber (OM2) were widely deployed in premises applications.
These fibers easily support applications ranging from
Ethernet (10 Mbit/s) to
gigabit Ethernet
(1 Gbit/s) and, because of their relatively large core size, were ideal
for use with LED transmitters. Newer deployments often use
laser-optimized 50/125 µm multi-mode fiber (OM3). Fibers that meet this
designation provide sufficient bandwidth to support
10 Gigabit Ethernet
up to 300 meters. Optical fiber manufacturers have greatly refined
their manufacturing process since that standard was issued and cables
can be made that support 10 GbE up to 400 meters. Laser optimized
multi-mode fiber (LOMMF) is designed for use with 850 nm VCSELs.
The migration to LOMMF/OM3 has occurred as users upgrade to
higher speed networks. LEDs have a maximum modulation rate of 622 Mbit/s
because they cannot be turned on/off fast enough to support higher
bandwidth applications. VCSELs are capable of modulation over 10 Gbit/s
and are used in many high speed networks.
Some
200 and 400 Gigabit Ethernet speeds use
wavelength-division multiplexing
(WDM) even for multi-mode fiber which isn't specified up to and
including OM4. In 2017, OM5 has been standardized by TIA and ISO for WDM
MMF, specifying not only a minimum modal bandwidth for 850 nm but a
curve spanning from 850 to 953 nm.
Cables can sometimes be distinguished by jacket color: for
62.5/125 µm (OM1) and 50/125 µm (OM2), orange jackets are recommended,
while
aqua is recommended for 50/125 µm "laser optimized" OM3 and OM4 fiber.
[4] Some fiber vendors use violet for "OM4+". OM5 is officially colored
lime green.
VCSEL power profiles, along with variations in fiber uniformity,
can cause modal dispersion which is measured by differential modal delay
(DMD). Modal dispersion is caused by the different speeds of the
individual modes in a light pulse. The net effect causes the light pulse
to spread over distance, introducing
intersymbol interference.
The greater the length, the greater the modal dispersion. To combat
modal dispersion, LOMMF is manufactured in a way that eliminates
variations in the fiber which could affect the speed that a light pulse
can travel. The
refractive index profile
is enhanced for VCSEL transmission and to prevent pulse spreading. As a
result, the fibers maintain signal integrity over longer distances,
thereby maximizing the bandwidth.
SOURCE
https://en.wikipedia.org/wiki/Multi-mode_optical_fiber
