FIGURE 1: For conventional cabling and to meet growing high-density and high-bandwidth demands, singlemode in high fiber
counts is increasingly being installed, though the need for multimode for the inside plant is still very necessary. From left to right,
examples include outside plant armored cable, indoor RoHS riser cable, indoor-outdoor riser, indoor interlocking armor plenum,
and rollable ribbon type cable.1
January/February/March 2020 I 37
will be compared in actual OSP and
inside plant installation examples so
that fellow designers and installers
can better understand these viable
installation methods in an age when
the enterprise customer confronts
ever-increasing bandwidth demands
and the continuous influx of
emerging technologies.
OPTICAL FIBER
COMPARISON BETWEEN
CONVENTIONAL AND
THE BLOWN FIBER SYSTEM
Optical fiber is categorized basically
in two types: singlemode and multimode.
Singlemode optical fiber (OS2-
low water peak) has a small, narrow
core of 8 to 10 microns (μm) and
allows for only one mode of light to
propagate, meaning that the number
of reflections are decreased as the
light travels through the core. This
enhances performance and lowers
attenuation/signal loss, thereby
allowing the signal to travel further.
Singlemode fiber (SMF) is optimized
at the 1310 nm and 1550 nm wavelengths.
Singlemode OS1 may still be
available from some manufacturers.
There is another type of low-water
peak singlemode optical fiber specified
in TIA, CENELEC and ISO/IEC
standards named OS1a that has
replaced the no longer recognized
OS1 cable. Both OS1a and OS2 use
the same low-water peak optical
fibers, but OS1a is typically tight
buffered for indoor use and typically
a loose tube construction for outdoor
use for conventional cabling installations.
Specifications for OS1a are for
cabled optical fibers, not bare fibers.
Therefore, OS2 is used with a blown
fiber system.
Multimode optical fiber has
a larger core than singlemode that
allows for multiple modes of light
to propagate, allowing for increased
reflections as the light passes through
it. Hence, it allows more data to pass
through it. However, the attenuation
rate increases as well as high dispersion
causing the signal to be reduced
as distances increase. Multimode fiber
(MMF) is available in several grades,
OM1 to OM5. Multimode OM1 is a
62.5 μm fiber and is still available but
no longer recommended as often for
today’s high-speed networks. Multimode
OM2 to OM5 is a 50 μm fiber
with OM3 and OM4 being laseroptimized.
The range of OM1 to OM4
operates at wavelengths of 850 nm
to 1300 nm. Designed to work over
a wide range of wavelengths between
850 nm and 950 nm, OM5 supports
shortwave wavelength division multiplexing
(SWDM).
For conventional cabling, both
SMF and MMF for the most part are
constructed in the same manner into
optical fiber cables; there is the core,
the cladding and the protective jacket.
All three parts can vary, especially
the outer jackets that must meet
the plenum and riser listing requirements
of the National Electrical Code
(NEC) as well as local codes. Over
the years, optical cable manufacturers
have designed cables for virtually
any application, including indoor-
outdoor loose-tube and ribbon, OSP
cables in metallic or dielectric, gel-
free, industrial cables, and a host of
many other configurations.
Both singlemode and multimode
cables can be ordered in a variety
of fiber counts from 2-to-288 fibers,
along with special order counts for
singlemode of 864 fibers as well as
newly designed rollable ribbon-type
cable of up to 3,456 fibers for high-
density applications (Figure 1).
Rather than housing and constructing
OS2 singlemode and OM1
to OM4 multimode into optical fiber
cables, as is done for conventional
cabling and the micro-cables used in