Choosing the Right Multimode Fiber for Data Communications

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workhorse for backbone fiber installations for many years, and is still present in legacy
systems.
Faster Transmission Rates, Higher Bandwidth Demands Drive Migration to 50 µm
While 62.5 µm fiber dominated the premises market for more than a decade,
changing market conditions have re-established 50 µm fiber as the best solution for
applications >10 Mb/s. The 100 Mb/s Fast Ethernet standard, published in 1995, called
for the use of LEDs that take advantage of lower fiber attenuation at 1300 nm
wavelength. This offset the LED coupling loss into 50 µm fiber caused by its smaller
core diameter; therefore, 50 µm fiber was able to support the same 2 km reach at 100
Mb/s as 62.5 µm fiber.
Only 3 years later, the IEEE Gigabit Ethernet standard published in 1998
specified low cost 850 nm wavelength Vertical Cavity Surface Emitting Lasers
(VCSELs) that can reach 1000 meters over 50 µm fiber, compared to 220-275 meters on
standard 62.5 µm. As data rates rise to multi-Gigabit speeds, it is apparent that 62.5 µm
fiber is stretched beyond its performance limit, due to its lower bandwidth at 850 nm. By
comparison, 50 µm fiber can provide as much as ten times the bandwidth of the 62.5 µm,
enabling more robust support of 1 Gb/s and 10 Gb/s applications. Because 1 Gb/s and 10
Gb/s transmitters use small spot-size lasers, concerns over power coupling efficiencies
into 50 µm fiber are no longer an issue.
The 10 Gb/s Ethernet standard, published in 2002, takes advantage of laser
optimized 50 µm fiber (OM3) that supports 300 meter reach using 850 nm VCSELs.
OM1 multimode fiber, in comparison, would support just 26 - 33 meters.