Enhancing Angle-Polished
Connector (APC) Performance
in the Outside Plant (OSP)
WHITE PAPER
Introduction
Fiber-to-the-premise architectures, by their very nature, require numerous fiber
connections for distribution of services to multiple home and business locations.
Much of the connectorization takes place downstream from the central office in
the outside plant (OSP) portion of the network, traditionally a splice-only
environment. However, as providers realize the cost-saving benefits – ease of
testing/troubleshooting, simpler network reconfiguration, faster service turn-up –
the need for higher performance of angle-polished connectors (APCs) in the OSP
environment has become a critical FTTP issue.
ADC has made great strides in enhancing its design and manufacturing processes
for APCs to provide customers with the highest level of connector performance in
OSP applications. This new breed of connector meets the increased performance
and reliability required by OSP portions of FTTP networks for offering triple play
services to consumers.
Enhancing Angle-Polished Connector (APC) Performance
in the Outside Plant (OSP)
Enhancing Angle-Polished Connector (APC) Performance in the Outside Plant (OSP)
Page 3
OSP Connector Concerns
Until the relatively recent interest in FTTP architectures, no
significant reasons dictated a need for APCs to push
performance limits. However, the trend toward pushing
fiber all the way to the customer premise has resulted in a
need for high-performance APCs that can withstand the
rigors associated with OSP implementation.
The sheer volume of OSP connectorization driven by FTTP
presents a challenge to APC connector manufacturers. For

(0.1 dB per connection for three connections).
In the outside plant, connectors with 0.1 dB initial loss that
can meet insertion loss change of 0.2 dB over
environmental extremes are available that could save 1 dB
(0.2 dB per connection for five connections). Connectors
are available in many styles and with either angled physical
contact or non-angled physical contact. Losses are not
significantly different between the two types, but costs for
the angled physical contact connector can be significantly
higher. The chief advantage over the non-angled physical
contact connector is the improved return loss performance
that results from the angled polish.
A tuning process improves insertion loss by improving the
alignment of the fiber cores in mated pairs. The accuracy
of the tuning process has a direct affect on randomly inter-
mated connector performance and is improved through
automated processes. Combined with consistent and
precise endface geometry, a higher level of optical
performance over time in an OSP environment can be
achieved.
Return loss, caused by changes in the index of refraction,
is also associated with each mated connector pair and
must be figured into the total loss budget. Higher
manufacturing standards can greatly reduce loss budgets
and, as a result, enable better performance over longer
distances in FTTP networks.
APC-Specific Issues for OSP
Deployment
There are a few specific concerns for achieving high
performance for APCs in the OSP portion of an FTTP

for connector reliability is ADC’s anti-rotational features
contained in its APC connectors. Changing and
inconsistent interfaces that allow ferrule rotation about
the ferrule axis have the potential to create air gaps
between the mated pair fiber cores, resulting in
significantly degraded, if not interrupted, service.
A small ferrule rotation can change the apex offset of an
APC connector by an unacceptable amount. Therefore, it
is critical that the connector be designed to minimize this
rotation while the connector is in service. Any air gap
created by a large apex offset will increase insertion loss
and reflectance, so keeping apex offsets as low as possible
is a critical issue for high-performance connectors.
The apex offset position is set during the polishing process.
Generally speaking, ferrules have a chamfer around the
endface that is symmetric with the axis of the ferrule.
However, when polished at 8 degrees, the apex of the
polished area changes with respect to the fiber core. As
more material is removed during polishing, the surface of
the endface becomes relatively larger on one side, moving
the center of the ferrule endface to one side and away
from the ferrule axis.
The peak, or apex, of this radius will generally be at the
center of the surface being polished, and the distance
between the center of the fiber and the center of the
spherical surface being polished is the apex offset. As this
peak drifts away from the ferrule axis as more material is
removed, the apex offset increases.
All APC SC connectors are designed to enable the ferrule
to float within the connector housing. This float is

and physical contact because the ferrule cannot remain in
a rotated state.
Several industry standards address acceptable
specifications for apex offset in APC connector endface
geometry. The predominant standard is IEC-60874-14-10
which defines apex offset to be less than 50 microns in
APC connectors. Likewise, the Telcordia GR-326, Issue 3,
also specifies a 50-micron maximum apex offset. A 50-
micron apex offset, when combined with the radius and
undercut requirements of these two documents, will
achieve the required glass-to-glass physical contact in
austere environmental conditions.
Temperature Variation
Temperature, particularly cold temperatures and wide
temperature variations, are directly related to insertion loss
failures due to cable and cable assembly component
shrinkage. ADC has designed its connector components to
overcome this challenge to prevent shrinkage, and even
fiber breakage, as a result of temperature in the OSP.
The environmental operating requirements for cable
assemblies in the North American market are defined by
industry standards. Telcordia GR-326, Issue 3, requires
cable assemblies to be subjected to two one-week thermal
cycle tests from -40 degrees C to +75 degrees C 21 times.
Each temperature extreme is held for a minimum one-hour
period, at which time the insertion loss and return loss are
measured. To meet the GR-326 requirement, insertion loss
cannot change more than 0.3dB at any time during the
test. ADC’s optical connectors meet the requirements of
GR-326, Issue 3.

temperature cycling, humidity exposure, and water
immersion.
Finally, a factory process audit ensures consistency of
product and performance across manufacturing facilities.
Through extensive testing processes, ADC ensures its
customers are deploying APCs specifically designed for the
OSP portion of the FTTP network – providing long service
life, reliability, durability, and the highest performance
available.