Fiber optics 2-4

1. CONNECTORS & SPLICES
Fiber optic connectors and splices are used to couple
two fibers together. Splices, however, are used to
connect two fibers in a permanent joint. Connectors
are also used to connect fibers to transmitters or
receivers, and, of course, connectors are designed
to be demountable. While they share some common
requirements, like low loss, high optical return loss
and repeatability, connectors have the additional
requirements of durability under repeated matings.
Splices, meanwhile, are expected to last for many
years through sometimes difficult environmental
conditions, perhaps underground, underwater or
suspended from aerial cables.

2. CONNECTORS & SPLICES
Since fiber optics began, over 80 different
styles of connectors have been used
commercially. Most have faded from use or
never became popular, so only a few
connector styles dominate today’s networks.
Multimode installations generally use the ST or
SC connector, with a growing number of SFF
(Small Form Factor) connectors.
Singlemode applications use mostly SC or
LCs, but many installations are still using
older designs.

3. CONNECTORS & SPLICES
DIFFERENT FIBERS = DIFFERENT
CONNECTORS
• Multimode
– ST or SC
– Small form factor
– Terminate in field
• Singlemode
– SC, LC, others
– Splice on factory-made pigtails

4. CONNECTOR SPECS
• Specifications
– Loss (in dbs)
– Repeatability
– Environment (temp, humidity, stress, etc.)
– Reliability
– Back reflection
– Ease of termination
– Cost

5. CONNECTOR SPECS
What’s important in the performance of a fiber optic
connector?
• Of course, the most important specification for a
connector is loss - the less light loss the better.
• But we also want the connector to be repeatable - in
two ways. If we terminate a lot of connectors, we
need to be assured that most have about the same
loss, so we can plan on that loss for calculating the
likely loss of the cable. (We’ll look at power budgets
later.) We also want it repeatable if we disconnect it
and reconnect it many times, so we know the loss
will not change when we reconnect it.

6. CONNECTOR SPECS
• Connectors must be designed to meet their specs
over the environmental changes it will see. It’s no
problem indoors, but outdoors, temperature and
humidity can change, and think about connectors on
an aircraft and the vibration they must endure!
• Reliability means maintaining low loss over its
lifetime.
• Back reflection is very important for Laser sources,
as light reflected back can disturb the performance
of the laser, plus reflected light can create optical
“background noise” which confuses receivers.
• Ease of termination and cost probably need no
further explanation.

7. CONNECTORS
Here are four generations of fiber
optic connectors, showing how
their size in particular has shrunk.
On the bottom is the Deutsch 1000,
one of the first commercial
connectors. It held the fiber by
vise-type action and connected
fibers in a plastic lens with oil in it
to assist the connection.
• Above it is a Biconic, AT&T’s first
commercial connector and the
first to work with SM fiber. The
Biconic ferrule is a glass-filled
thermoplastic. For
• The SC from NTT in Japan was
one of the first to use ceramic
ferrules and have very low loss,
even with SM fiber. It’s still widely
used today.
• The LC uses a very small ceramic
ferrule to allow the connector to
be so small, and it offers equal or
perhaps even better performance
than the SC.
LC
SC
Biconic
Deutsch

8. CONNECTOR IDENTIFIER
ST (an AT&T Trademark) is
probably still the most
popular connector for
multimode networks, like
most buildings and
campuses. It has a bayonet
mount and a long cylindrical
ferrule to hold the fiber. Most
ferrules are ceramic, but
some are metal or plastic.
And because they are spring-
loaded, you have to make
sure they are seated
properly. If you have high
loss, reconnect them to see
if it makes a difference.
ST CONNECTOR

9. CONNECTOR IDENTIFIER
SC is a snap-in connector
that is widely used in
singlemode systems
for it's excellent
performance. It's a
snap-in connector that
latches with a simple
push-pull motion. It is
also available in a
duplex configuration. SC CONNECTOR

10. CONNECTOR IDENTIFIER
The NTT FC/PC has been one of the
most popular singlemode
connectors for many years. It
screws on firmly, but make sure
you have the key aligned in the
slot properly before tightening.
It's being replaced by SCs and
LCs.
The NEC D4 was one of the first SM
connectors and is rarely used - at
least in the US - for new
installations today.
FC CONNECTOR
D4 CONNECTOR

11. CONNECTOR IDENTIFIER
The SMA was developed by Amphenol from
a microwave connector (SMA means
sub-miniature A type) with an 1/8 inch
metal ferrule. It came in two varieties -
the 905 with a straight ferrule and the
906 with a necked-down ferrule that
used a Delrin alignment bushing. The
SMA is obsolete but still commercially
available to support old systems. It’s
very rugged and still liked for harsh
environments.
The AMP Optimate was one of the first
commercial connectors. It used a
conical plastic ferrule to align fibers. It’s
also obsolete and practically impossible
to find anymore.
SMA CONNECTORS
AMP OPTIMATE
CONNECTOR

12. CONNECTOR IDENTIFIER
Besides the SC Duplex, you may
occasionally see the FDDI and
ESCON* duplex connectors which
mate to their specific networks.
They are generally used to
connect to the equipment from a
wall outlet, but the rest of the
network will have ST or SC
connectors.
*ESCON is an IBM trademark
FDDI CONNECTOR
ESCON
CONNECTOR

13. CONNECTOR IDENTIFIER
LC is a new connector that uses a
1.25 mm ferrule, half the size of
the SC. Otherwise, it's a standard
ceramic ferrule connector, easily
terminated with any adhesive.
Good performance, highly
favored for singlemode.
MT-RJ is a duplex connector with
both fibers in a single polymer
ferrule. It uses pins for alignment
and has male and female
versions. Multimode only, field
terminated only by
prepolished/splice method.
LC CONNECTOR
MT-RJ CONNECTOR

14. CONNECTOR IDENTIFIER
Opti-Jack is a neat, rugged duplex
connector cleverly designed
around two ST-type ferrules in a
package the size of a copper RJ-
45. It has male and female (plug
and jack) versions. It uses
adhesive or prepolished/splice
termination.
Volition is a slick, inexpensive
duplex connector that uses no
ferrule at all. It aligns fibers in a
V-groove like a splice. Plug and
jack versions are available, but
you can field terminate jacks only.
OPTI-JACK
VOLITION
CONNECTOR

15. CONNECTOR IDENTIFIER
• MU looks a miniature SC with a
1.25 mm ferrule. It's more popular
in Japan.
• E2000/LX-5 is like a LC but with a
shutter over the end of the fiber.
High power system users like
DWDM and CATV like it for the
safety factor of the shutter.
MU CONNECTOR
LX5 CONNECTOR

16. CONNECTOR IDENTIFIER
• MT is a 12 fiber connector for
ribbon cable. It's main use is for
preterminated cable assemblies
which can be installed as
complete systems to avoid field
terminations.
MTP CONNECTOR

17. CONNECTOR IDENTIFIER
Since so many
connectors use the
2.5 mm ceramic
ferrule, you can
cross-mate them with
adapters like these.
You can get adapters
for ST to FDDI and
ESCON also.
ST-FC >
SC-FC >
SC-ST >