Optical
fiber is utilized for high-speed and error-free data transmission
across connector assemblies. So the connector end faces need to be
polished to optimize performance. And also the connectors must follow
acceptance criteria related to insertion and back reflection loss as
well as end-face geometry specifications. This article will talk about
the fiber optic connectors polishing.
Polishing Process
Early
physical contact connectors required spherical forming of their flat
end faces as part of the polishing procedure. It involved a four-step
process: epoxy removal, ferrule forming, and preliminary and final
polishing. These steps utilized aggressive materials for epoxy removal
and ferrule forming, generally accomplished with diamond polishing
films. Now the polishing process has developed into a sequence of epoxy
removal, followed by rough, intermediate and final polishing cycles
because almost all connectors are manufactured with a pre-radiused end
face. One goal is to avoid excessive disruption of the spherical
surface, while still producing a good mating surface.
Polishing Specifications
Polishing
specifications for fiber connectors fall into two categories related to
performance and end-face geometry. Back reflection and insertion loss
specifications are the most critical measures of polished end
functionality. The insertion loss is the amount of optical power lost at
the interface between the connectors caused by fiber misalignment,
separation between connections (the air gap) and the finish quality of
each connector end. The current standard loss specification is less than
0.5 dB, but less than 0.3 dB is increasingly specified. Back reflection
is the light reflected back through the fiber toward the source. High
back reflection can translate to signal distortion and, therefore, bit
errors in systems with high data transfer rates.
Polishing Material
Today
several types of connectorized fibers are available, the most common of
which are 2.5 mm, 1.25 mm and multifiber. Connector end faces must
first be air-polished to ensure a proper mating surface. This will be
followed by a sequence of polishing steps depending on the type of
connector, the back reflection and the insertion loss specifications.
Regardless of the connector type, most polishing sequences begin with
aggressive materials, including silicon carbide to remove epoxy and
diamond lapping films for beginning and intermediate polishing. These
remove both surrounding material and fiber at the same rate. But the
last polishing step needs a less aggressive material to attack only the
fiber, such as silicon dioxide. Using a material for final polishing
that is too aggressive could result in excessive undercut. The wrong
final-polish material can cause excessive protrusion, leading to fiber
chipping and cracking during the connector mating process.
Impact Factor
Issues
to be examined include the polishing films used, the type of epoxy and
lubrication. Films are the most significant impact because the
gradations and quality vary from supplier to supplier. End users should
pay attention on selecting film type. Excessively aggressive films can
destroy a 125-μm fiber and the end-face radius. Epoxy removal is also
essential to contamination-free polishing. Some types of epoxies can be
removed more easily with specific grades of silicon-carbide polishing
films. The films to use in this step depend on the size of the epoxy
bead mounted on the connector end face and the epoxy type. Epoxies have
different varieties. Some will be tacky, some firm. In all, a
contamination-free environment is essential to optimizing connector
polishing.
Polishing
may be an old art form, but for the immediate future, it’s here to
stay. Undoubtedly inspection criteria will increase. Polishing
procedures will be driven to change, and new connector style will also
make us continuously strive to reinvent our approach to polishing.
Fiberstore has various products about fiber optic polishing. For more
details, please visit FS.COM.
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