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Polishing film and pads – choosing the right combination for your application

Nov. 2, 2022, 7:39 p.m.

Dialing in a process for fiber optic polishing machines can be an intensive task, especially if your knowledge regarding polishing films is limited. There is no getting around it, polishing films are required for polishing. Being able to choose the right film to get optimal polish quality takes experience and extensive knowledge regarding polishing film types. The objective of this blog post will be to educate you on polishing films: the varieties and types, along with their unique characteristics.

Polishing film types are selected to carefully remove fiber material at a controlled rate and degree of aggressiveness.  Each unique polishing application generally requires experimentation to figure out which polishing films yield the optimal fiber or connector finish. For instance, silicon carbide and aluminum oxide are film types best used for epoxy and material stock removal or when a pristine finish is not required. These film types are low cost for this reason. Typical abrasive particle sizes range from 0.3 microns to 30 microns. For extensive material removal and/or large surface areas, abrasives with >400 grit are also available.

The first step in understanding polishing films is knowing the importance of silicon carbide polishing film and aluminum oxide polishing film. These two different types of film are important because they are extremely useful for polishing glass fibers terminated in metal ferrules and connectors. Silicon carbide typically cuts faster than aluminum oxide. For the same particle size, aluminum oxide typically yields a better surface finish than silicon carbide. Silicon carbide is good for polishing glass fibers and plastic optical fibers (POF) with either flat or angled endfaces.  While silicon carbide and aluminum oxide film types can be used for ceramic ferrule terminated fibers, its use will tend to result in a fiber “undercut.” This is due to the particle material type embedded in the film.  They are simply not aggressive enough to significantly remove the ceramic material. Hence the fiber becomes undercut, resulting in its surface being slightly lower than the ceramic. Depending on application, this may result in unwanted back reflections and greater attenuation due to the gap between the fiber surfaces of the two mated connectors. When it comes to this issue, there is a solution.

That brings us to our second step in understanding films and their use with fiber optic polishing machines. This is the importance of polishing films containing diamond particles. Diamond films differ from the first two film types we learned about in many ways. The two most important differentiations I want you to know about are its cost (more costly) and aggressiveness (more aggressive). Diamond film types are aggressive enough to polish hard materials such as ceramic, sapphire, and tungsten carbide. Hence if polishing a fiber terminated on a ceramic ferrule, the diamond film will cut both the ceramic and fiber at approximately the same rate, resulting in a planar fiber/ferrule endface. This eliminates the possibility of the undercut problem I mentioned earlier. Additionally, diamond films can shape ceramic ferrule endfaces while aluminum oxide and silicon carbide would not be aggressive enough to do so (also mentioned earlier). APC connectors require an angled endface (typically 8 deg). Diamond films are aggressive enough to cut this angle. Diamond film also has a longer polish life and a technician can get more cycles per set of connectors being polished.

Finally, our third and final step in understanding polishing films could be argued as the most important. This major factor of polishing is the surface upon which the film is placed on. This is critical when trying to create a sharp angle or radius on the fiber. Depending upon the hardness of the surface which the film is placed, polishing films can shape fibers and ferrule endfaces to desired geometries. For instance, if a flat endface is needed, we at KrellTech would suggest using a glass plate as the polishing surface. Softer rubber pads (such as KrellTech’s hybrid pads) can achieve a radius and generate industry accepted ferrule endface geometries such as Telcordia GR326.

Most film is available with PSA (pressure sensitive adhesive) and non-PSA configurations. PSA films have a sticky backing which makes it easy to apply to a glass plate or hybrid disk. A light spray of water on the polishing plate/pad allows the non-PSA film versions to adhere.

Being a polishing equipment manufacturer, KrellTech offers an extensive line of fiber optic polishing films and precision rubber pads/glass disks. Contact a KrellTech representative to identify the best film/pad for your application. We at KrellTech promise to continue to strive to assist technicians, engineers and our customers using fiber optic polishing film.

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