Benefits of Fiber Optic and Passive Optical LAN Test

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Benefits of Fiber Optic and Passive Optical LAN
Test-Mark Mullins
www.flukenetworks.com 2006-2017 Fluke
Corporation
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Benefits of Fiber Optic and Passive Optical LAN
Test
In recent years, passive optical LANs have
gained significant popularity as an alternative
to horizontal copper structured cabling in a
variety of enterprise spaces. The technology
brings fiber out of the riser backbone and data
center, and with that comes the need for fiber
technicians to test these systems out in the
horizontal space. Lets take a closer look at
these passive optical deployments.
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Benefits of Fiber Optic and Passive Optical LAN
Test
How Do They Work?
Passive optical LANs are a point-to-multipoint
fiber architecture that use passive optical
splitters to divide the signal from one
singlemode fiber into multiple fiber signals. The
signals are transmitted simultaneously in both
directions over separate wavelengths using
wavelength division multiplexing (WDM)
technology1310nm for upstream data and 1490nm
for downstream data. Available in a variety of
split ratios such as 18, 116, and 132, optical
splitters basically serve the same purpose as a
network switch, but they are not electrically
poweredthats why the technology is referred to
as passive.
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Benefits of Fiber Optic and Passive Optical LAN
Test
How Do They Work?
The singlemode fiber that arrives at the
splitter originates at an optical line terminal
(OLT) typically located in a data center or main
equipment room. From the splitter, multiple
fibers connect to optical network terminals
(ONTs) that convert the optical signal into
multiple balanced signals for transmission over
twisted-pair copper cabling to end devices.
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Benefits of Fiber Optic and Passive Optical LAN
Test
What are the Benefits?
Because passive optical LANs use singlemode
fiber, they are not limited by the 100-meter
channel distance of copper but instead can reach
distances of 20 kilometers. This is ideal for
large facilities, or really any facility where
100 meters is not feasible. In addition to
eliminating the distance limitation, the primary
cost-saving benefits of passive optical LANs
include the ability to eliminate
telecommunications rooms and the associated power
and cooling infrastructure. The smaller, lighter
singlemode fiber cables used in these systems
also reduces pathway and space requirements. Othe
r benefits touted by proponents of passive
optical LANs, and of fiber systems in general,
include improved security and eliminating the
crosstalk and EMI/RFI concerns associated with
copper cabling.
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Benefits of Fiber Optic and Passive Optical LAN
Test
How are they Tested?
Just like any fiber optic system, a passive
optical LAN requires insertion loss testing. And
just like any fiber system, the overall channel
loss is based on the end-to-end path between
application specific equipmentthe OLT and ONT in
the case of the passive optical LAN. That means
that everything in betweencable, connectors,
splitters, and splicesattributes to loss.  And
just like any fiber optic system, connector
cleanliness remains vital. That means the
connectors should be inspected for
contamination. For passive optical LANs, the
acceptable insertion loss is a minimum of 13dB
and a maximum of 28dB at a 20km distance. The
singlemode fiber used in a passive optical LAN
should also be tested at both the 1310nm and
1490nm wavelengths. And test reference cords must
include the angled polish contact (APC) style
connector to match those used in passive optical
LANs. Best practices for passive optical LAN
testing will be included in the upcoming
international standard IEC 61280-4-3, which in
keeping with existing TIA and ISO/IEC standards,
specifies a light source/power meter for Tier 1
testing and an OTDR for Tier 2 testing in the
upstream direction.
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