and Splice Loss Testing
fiber optics, a single connector has no loss. The
"loss of a connector"
is defined as a "connection loss" caused by a mated
pair of connectors.
The lab method used to establish the average loss
value of a connector
design is shown below. The loss of connectors on a
patchcord or short
cable is given by FOTP-171 and the loss of an
plant is measured by OFSTP-14 (MM) or OFSTP-7 (SM.)
order to establish a typical loss for connectors, it is
necessary to test all connectors in a standardized
connector or splice losses are performed by measuring
power of a short length of cable and then inserting a
pair or splice into the fiber and measuring the change
of loss as a
result of adding a connection. This test ( designated
by the TIA) can be used for both multimode and
but the results for multimode fiber are very dependent
has three options in modal distribution: 1)EMD
modal distribution or steady state) , 2) fully filled,
and 3) any
other conditions as long as they are specified. Besides
distribution factors, the uncertainty of the measured
a combination of , inherent fiber geometry variations,
connector or splice characteristics, and the effects of
the splice bushing
used to align the two connectors.
test is repeated hundreds or thousands of times by each
connector or splice manufacturer, to produce data that
shows the repeatability
of their connector design, a critical factor in figuring
for installations using many connectors. Thus loss is
only criteria for a good connector, it must be
its average loss can be used for these margin
some degree of confidence.
and Splice Durability
factor important to a connector is the durability of
the design, shown by its ability to withstand many
degradation in loss. Testing connector durability is
matter of repeated mating and demating of a connector
measuring loss. Since the loss is a function of both
and alignment sleeve, it is helpful to determine which
contributors to degradation. Plastic alignment sleeves,
with ceramic connectors, for example,will usually wear
faster, shaving plastic off onto the connector ferrules
increased loss and return loss. When testing durability,
inspection of the connector end faces and ferrules with
to determine wear or contamination is very important.
durability is one of withstanding many cycles of
stress, since splices are often used in splice
enclosures in pedestals
or mounted on poles where they are exposed to the
climatic changes. Manufacturers usually test a number of
through many environmental cycles and accelerated aging
their durability. Such tests may take years.
you have ever looked at a fiber optic connector on an
you are familiar with the characteristic spike that
the connector is. That spike is a measure of the
(sometimes also called optical return loss) of the
connector, the names used for the amount of light
that is reflected back up the fiber by light reflections
interface of the polished end surface of the connector
It is also called fresnel reflection and is caused by
the light going
through the change in index of refraction at the
the fiber (n=1.5) and air (n=1).
return spike is one component of
the connector's loss, representing about 0.3 dB loss for
a non-contact or air-gap connector (two air/glass
interfaces at 4% reflection each), the minimum loss for
connectors without an index-matching fluid. But in
singlemode systems, that reflection can be a major
source of bit-error
rate problems. In some singlemode systems, the reflected
light interferes with the laser diode transmitter,
causes mode-hopping and can be a source of noise.
the light reflected back into the laser is necessary to
performance out of high bit rate laser systems,
AM modulated CATV systems. In multimode systems,
reflections can add to background noise in the
this is more a problem with singlemode systems,
have concentrated on solving the problem for their
components but multimode connectors benefit also.
Several schemes have
been used to reduce reflectance, mainly reducing the gap
connectors to a few wavelengths
of light using a physical contact (PC) polish on the end
connector ferrule, which reduces the fresnel reflection.
involves polishing the end surface of the fiber to a
or at a slight angle to prevent direct back reflections.
Another, even more effective solution, is to
polish the end of the singlemode
connector ferrule at a small angle (about 8 degrees) to
reflected light to be absorbed in the fiber cladding.
called angle-polish connectors (APC) and are widely used
for CATV and
high big rate digital systems.
on different methods of reflectance testing.