Telecommunications
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Ceramic materials are used
in a wide range of applications in this industry. The
main use of zirconia is for ferrules and sleeves for connecting
fibre optic cables.
The excellent surface finishes and strengths which are
attainable with TZP"s has led to their use in optical
fibre technologies where they are used as split coupling
devices for optical fibres.
In parallel with the injection moulding technology which
has been developed to produce such components, diamond
finishing techniques have also been improved to allow
tolerances of 1 micron to be achieved on a repeatable
basis.
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Typical telecommunications components |
Ferrule
Singlemode connectors have ferrules which align the fibre cladding
to the centre axis of the ferrule to within 1 - 2 micron. To
achieve this, the connector hole diameter is carefully matched
to the actual fibre diameter ( e.g. hole size 124, 125, 126
micron ). Alternatively a larger hole with some form of active
alignment procedure is used.
Singlemode connectors tend to be expensive to manufacture,
and time consuming to assemble.
Multimode connectors have ferrules with e.g. a 128 micron hole
for nominally 125 micron fibre, so they are relatively easy
to make and assemble.
Some multimode ferrules are made of plastic or stainless steel,
which can provide adequate tolerances for multimode application.
However neither of these are suitable for test leads, due to
increased wear and generally worse tolerances.
The manner in which the ferrule is polished is critical to
return loss performance of singlemode connectors.
A "flat polish" connector will cause around -14.7
dB return loss unmated, and up to -11.7 dB mated. ( e.g. two
reflections ). A "PC" or "physical contact"
connector will cause around -14.7 dB return loss unmated, and
between -30 and -60 dB mated.
The mated performance is very variable between polishing procedures
(and operator experience), and also very sensitive to dirt and
wear. Therefore, the so-called "super PC" or "ultra
PC" polish connectors need constant measurement to verify
their achieved performance. Also, their poor unmated performance
limits their effectiveness in many applications.
Improvements can be achieved by using "APC" or "angled
physical contact" polish connectors, which offer better
than 60 dB return loss in all circumstances ( unless the fibre
tip is dirty ).
Alignment Sleeve
The alignment sleeve is located in the through connector, and
is used to align the ends of 2 ferrules so that the cores of
the 2 fibres are aligned.
Alignment sleeves for singlemode fibre are generally made from
beryllium copper or ceramic.
Whereas under ideal conditions ceramic provides lower loss
performance, the beryllium copper sleeves tend to be more forgiving
of tolerance variations when mating connectors between different
manufacturers. Metal alignment sleeves can bend, and then cause
poor performance.
Why Zirconia?
Zirconia ceramic ferrules offer distinct advantages:
• chip and crack free
• smaller grain sizes achieve smoother finishes
• thermal expansion coefficient closer to that of the fibre
• a higher modulus of elasticity and
• greater impact resistance.
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