Polishing Tips and Best Practices for Single Fiber Connectors

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 When polishing a fiber optic connector,
by polishing
machine, there are procedures and setting parameters designed to
leverage the machines best practices as well as previous developments and
experience.

 

Additionally, there are tips to
consider applying during daily production to improve first pass yield,
efficiency and results to avoid scrapping costs.

 

The standard polishing process includes
three steps:

 

Epoxy Removal

Geometry

Final Step: finishing the optical
surface

Below we share tips for each step of
the process:

 

Epoxy removal

Air Polish

When connectors are loaded on the jig
after cleaving, there are large, sharp edge fibers and inconsistent fiber
protrusion due to different fiber cleaves. 
This can result in fiber breaks if polishing, by machine, is started
immediately.

 

Tip: start polishing the connectors
loaded on the jig with SC Film mounted on the rubber pad and then by hand/air
delicately, with little hand pressure making few rotations (around 10).  Next the fiber protrusion has more consistent
length distribution over all ferrules resulting in less fiber breakage (fiber
into ferrule bore hole).  After this
initial operation, one can start polishing with the machine using the same film
used for air polishing.

 

LC Conical

The available surface of the 1.25 mm
connector is small and sometimes due to this limited surface, epoxy is also
going to the base of the chamfer area that you cannot remove using the
polisher.

 

Tip: After the epoxy removal step on
the polisher, if some epoxy is still present on the chamfer area, use a little
scalpel to remove residues. This will allow to move to the next step (Geometry)
avoiding any contamination on D films.

 

For other types of ferrule (2.0 or 2.5
mm) it is a good practice to check, after epoxy removal, if all the epoxy has
been polished away (checking the front face of the ferrules).

 

Jig Locking Mechanism with Individual
Ferrule

A jig where the ferrules are
independently moving from the each other is called Individual Pressure Control
(IPC) fixture and is recognized by the use of spring loaded adapters to lock
and to keep the ferrule in place.

 

Tip: after checking if there are not
any epoxy residues left, it is a good practice to verify if all the connectors
are well positioned (same height) and if the spring of each adapter is working
properly with the ferrule moving freely – not stuck due to polishing residue.
This guarantees each ferrule will be under the defined polisher pressure in the
polishing steps offering more consistent geometry results.

Geometry

 

Air Bubble Under Lapping Film

A common occurrence after positioning
on the rubber pad is air bubbles under the lapping film.

 

When this occurs, it must be removed
because during the geometry polishing process as the air cushion can modify the
ferrule geometry (radius and/or apex).

 

Tip: to avoid this effect, use a roller
to press down the lapping film on the rubber pad. It is important to have a
different roller for each type of film to avoid contamination especially from D
film to final film.  If one uses the same
roller, it is essential to clean it before moving to the smaller film grid.

 

Tip: when using just one roller, to
avoid contamination, take two films one on top of the other (one on top upside
down) and then use roller. The lapping film that will used for polishing
connector will not be effected by any cross-contamination.

 

D Film Longer Life

Diamond film is the most expensive film
we use on the polishing process and one consideration when selecting a supplier
is the number of times you can use it.  
There are D films used for 10, 15, 25 times, or even longer depending on
the process and specific customer specifications.

 

Tip: after a certain number of usage,
typically 10 times, if you clean the surface with alcohol you are able to
extend the life of this film (using alcohol removes debris from previous
polishing).

VIEW: Diamond Films Product Matrix

 

 

Rubber Pad

In a polishing process, we use rubber
pads typically 60 to 80/85 durometer. 
Keeping consistent geometry can be a challenge.

 

In principle, a rubber pad that is too
soft can help to reduce radius but effect negatively the apex.

 

Using a harder pad with higher pressure
should be better to get positive radius and apex results.

 

Tip: always try to develop a process
using pads with same durometer throughout the entire process. Changing the
hardness of the pad will effect radius and/or apex and can make it difficult to
bring both parameters within the specification. 
Usually adjusting pressure and timing, using the same pad, can achieve
desired results.  If you do need to
change to a softer pad, decrease the durometer maximum by approximately 10
durometer.

 

APC Jig Choice According to Connector
Style

In the market there are two different
types of ferrules: Stepped and Conical.

 

As soon as you select the connector
style, you need to consider the related jig.

 

Tip:

Stepped Ferrule – require a jig with an
APC angle of 8°

Conical Ferrule – require a jig with an
APC angle of 8.3°

 

FINAL STEP

 

CLEAN, CLEAN, CLEAN

Scratches are a fiber optic assembler’s
nightmare because if it occurs, they jeopardize all of the previous activities
and are costly due to the waste of time and additional material.

 

Tip: each step requires good
cleanliness to avoid contamination especially when you move from D film to
Final film.   Quite often this activity
is underestimated but if you make this a priority, you can avoid costly issues.

 

Tip: use spray water to remove all the
debris on the ferrule and mainly at the jig’s bottom surface.   Follow this by wiping the operation using
Cleaning Wipes or similar paper moving from the center of the jig to the
outside.

 

Final Film Choice

In addition to the nice smooth surface,
final film is extremely important to define the right fiber protrusion.  Based on the requested specification, you can
choose different types of film that provide various results.

 

Tip: important to know the different
specifications and what your requirement is: Fiber protrusion, Undercut,
Flatness with respect to the Ferrule.  
Basically, fibers can protrude or stay below the ferrule surface
according to the described parameter to guarantee the best fiber physical
contact terminated in a connector.

Tip: if you don’t have access to
different final films, adjusting time and pressure, can also achieve specified
results with some limitations.

 

Fiber optics requires physical contact
between the two mating parts because if you have an air gap between, it will
cause high back reflection.  The physical
contact will happen when you have fiber protrusion but considering the
compression force made by the connectors, you could have some physical
deformation of the fiber and ferrule. 
When that happens, there is physical contact with flat and undercut if
the related value are according to the specified parameters.

 

One might ask, why not only use protruding fiber
and the answer is that concern is about fiber breaks when the two fibers are
pushed against the others?   They specify
undercut or flat fiber vs. end face the ferrule to better protect the fiber but
still having physical contact.  It is
clear the parameters have to be according to the specifications (as seen on the
graphic) otherwise you will experience air gap.