Fiber optics 2-6

1. FIBER OPTIC SPLICES
• While connectors are demountable, splices are
permanent connections.
• Splicing is only needed if the cable runs are too long
for one straight pull or you need to mix a number of
different types of cables (like bringing a 48 fiber
cable in and splicing it to six 8 fiber cables - could
you have used a breakout cable instead?)
• And of course, we use splices for restoration, after
the number one problem of outside plant cables, a
dig-up and cut of a buried cable, usually referred to
as “backhoe fade” for obvious reasons!
• They may have different uses, but the basic
specifications for splices are the same as for
connectors.

2. FIBER OPTIC SPLICES
• Permanent terminations
for fiber
• Specifications
– Loss
– Repeatability
– Environment
– Reliability
– Back reflection
– Ease of termination
– Cost

3. FIBER OPTIC SPLICES
• There are two types of
splices, fusion and
mechanical.
• Fusion splicing is done
by welding the two fibers
together, usually with an
electrical arc with an
automated splicer which
aligns the fibers exactly.
It has the advantages of
low loss, high strength,
low back reflection
(optical return loss) and
long term reliability.

4. FIBER OPTIC
SPLICES
• Mechanical splices use an
alignment fixture to mate
the fibers and either a
matching gel or epoxy to
minimize back reflection.
Some mechanical splices
use bare fibers in an
alignment bushing, while
others closely resemble
connector ferrules without
all the mounting hardware.
• While fusion splicing
normally uses active
alignment to minimize
splice loss, mechanical
splicing relies on tight
dimensional tolerances in
the fibers to minimize loss.

5. FIBER OPTIC SPLICES - FUSION
Fusion splicers are expensive,
fully automated machines
that do most of the work.
The operator uses a high
quality clever to prepare the
fibers and inserts them into
the jaws of the splicer. The
machine automatically
aligns the ends, makes the
splice and even gives an
estimate of the loss. The
operator then places the
splice in a holder which also
seals it and inserts it in a
splice tray.

6. FIBER OPTIC SPLICES - FUSION
While fusion splicers are
expensive($5000+), but
each splice is cheap. So
if you are doing lots of
splices, fusion is more
cost effective.

7. FIBER OPTIC SPLICES -
MECHANICAL
Mechanical splices, like this Ultrasplice, use some
mechanical alignment fixture, a glass capillary in
this case, and some means of securing the fibers
in the splice. Mechanical splices are more common
with multimode fiber.
Mechanical splices are more expensive, but the
equipment necessary is relatively inexpensive. So
if you are only making a few splices, mechanical is
the less expensive choice.

8. FIBER OPTIC SPLICES -
CLEAVING
In order to get good fiber
optic splices or
terminations, especially
when using the pre-
polished connectors with
internal splices, it is
extremely important to
cleave the fiber properly.
The term “cleave” is
somewhat confusing, as is
the terminology for the
tool that does the job, so
lets define our terms and
look at how the process is
done properly.

9. FIBER OPTIC SPLICES -
CLEAVING
• Cleaving is the process by which
an optical fiber is “cut” or
precisely broken for termination
or splicing. Just like cutting
glass plate, fiber is cut by
scoring or scratching the surface
and applying stress so the glass
breaks in a smooth manner along
the stress lines created by the
scratch. Properly done, the fiber
will cleave with a clean surface
perpendicular to the length of the
fiber with no protruding glass on
either end (called a lip) and no
surface roughness (hackle or
mist.)

10. FIBER OPTIC SPLICES -
CLEAVING
A cleaver is a tool that holds the fiber
under low tension, scores the surface
at the proper location, then applies
greater tension until the fiber breaks.
Good cleavers are automatic and
produce consistent results,
irrespective of the operator. The user
need only clamp the fiber into the
cleaver and operate its controls.
Some cleavers are less automated,
for example requiring operators to
exert force manually for breaking the
fiber, making them more dependent
on operator technique and therefore
less predictable.

11. CONNECTOR & SPLICE LOSS
• Connector loss is
minimized when the
two fiber cores are
identical and perfectly
aligned, the connectors
or splices are properly
finished and no dirt is
present. Only the light
that is coupled into the
receiving fiber's core
will propagate, so all
the rest of the light
becomes the connector
or splice loss.

12. CONNECTOR & SPLICE LOSS
End gaps cause two
problems, insertion
loss and return loss.
The emerging cone of
light from the connector
will spill over the core
of the receiving fiber
and be lost. In addition,
the air gap between the
fibers causes a
reflection when the light
encounters the change
in refractive index from
the glass fiber to the air
in the gap.

13. CONNECTOR &
SPLICE LOSS
The end finish of the fiber must be properly polished to
minimize loss. A rough surface will scatter light and dirt
can also scatter and absorb light.
Since the optical fiber is so small, typical airborne dirt can be
a major source of loss. Whenever connectors are not
terminated, they should be covered to protect the end of
the ferrule from dirt. One should never touch the end of
the ferrule, since the oils on one's skin causes the fiber to
attract dirt. Before connection and testing, it is advisable to
clean connectors with lint-free wipes moistened with
isopropyl alcohol.

14. CONNECTOR &
SPLICE LOSS
Two sources of loss are directional; mismatches in numerical
aperture (NA) and core diameter. Differences in these two
will create connections that have different losses
depending on the direction of light propagation.
Light from a fiber with a larger NA will be more sensitive to
angularity and end gap, so trans-mission from a fiber of
larger NA to one of smaller NA will be higher loss than the
reverse.
Likewise, light from a larger fiber will have high loss coupled
to a fiber of smaller diameter, while one can couple a
small diameter fiber to a large diameter fiber with minimal
loss, since it is much less sensitive to end gap or lateral
offset.