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Last Updated: August 17, 2022

Marcel BuijsMarcel Buijs, EMEA Business Development, Technical Sales, Fiber Optic Center, Inc. with over twenty five years in the photonics industry, brings this latest information on making the ultimate fiber optic product and improving process yield.

The cleaning activities for fiber optic connectors can be divided into two different “fields”:

  1. During the manufacturing stages in the fiber optic cable assembly process
  2. During installation for fiber optic applications such as data communications, laser processing, sensors, etc.

In both activities, the cleanliness of the connector is paramount to guarantee end face quality as well as the quality of the optical signal. To this end, there are specific cleaning techniques that production teams and installation technicians should follow. Therefore, this article is a helpful resource whether you run a fiber optic cable assembly operation OR install patch cords, cassettes, cabinets, sensors at datacenters, telecom companies, measurement networks, high power laser applications etc.

Even if you and your team follow a good cleaning regimen, take a few minutes to review this article to ensure you’re properly cleaning the fiber optic connector at every step. A connector with a scratch through the core of an optical fiber can be so damaged that it will need to be replaced in the field, which can be time-consuming and expensive.

The art of cleaning during the assembly process

In many stages during the fiber optic cable assembly process a connector is cleaned to prevent damages (such as scratches) and prevent faulty measurements.

Cleaning takes place in the following production steps:

  1. Between polishing steps and after final polish
  2. Before and during the visual inspection (after polishing the connector)
  3. Before end face geometry measurement
  4. Before optical testing
  5. During final inspection before capping and packaging

Specific cleaning techniques to use between polishing steps and after the final polishing step

The objective of each cleaning action during the polishing process is to remove residue from the connectors’ end face as well as the fixture surface. (Polishing residue can include diamond or aluminum oxide grit, ceramic or silica material from the ferrule, and glass residue from the optical fiber.) Removing residue throughout the polishing process prevents cross-contamination, which can scratch the fiber during subsequent polishing steps.

Note that cleaning is performed without using an inspection microscope. Therefore, you must take time to carefully view the appearance of the fixture and connectors. Look for a clean surface on the connectors, without any polishing debris. And look for a white mist on the fixture surface.

Follow these tips between polishing steps:

  • Spray DI water with a spray bottle on the fixture surface and gently remove any debris with a Kimwipe. Be sure to wipe all the connectors as well as the polishing fixture, since the entire fixture gets contaminated with polishing grit.
  • If you use the Domaille cleaning wand, the spraying can be done with this water/air gun. Afterward, carefully wipe the connectors and fixture surface with a Kimwipe.
  • After the final polishing step, thoroughly clean the connectors and complete fixture surface (as in the previous in-between steps), then dry the surface using an air gun. Next, drench a Kimwipe with special cleaning fluid and clean all connectors in a circular motion. Use of IPA is common, and can have good results, but does have the potential of creating static charge on the ferrule end-face which will have the effect of turning the end-face into a dust-magnet.

Specific cleaning techniques to use during all production steps after polishing

The main objective with cleaning action after the polishing process is to ensure there is no contamination while the connector is verified during geometry or optical measurement. During visual inspection, any contamination should be located and identified while the visual aspects of the connector are verified and the passing connector is subjected to subsequent process steps such as geometry and optical measurement. The end face is inspected using the appropriate magnification. In many cases, the magnification and inspection criteria are described in documents provided by one of the standardization bodies.

Depending on the type of contamination detected, thoroughly clean the connector using one of the techniques below:

  • Use dry cleaning for light debris, dust, or black spots – Use a dry wipe with a cleaning cloth or reel cleaner. If the contaminant can’t be removed by dry cleaning, use the wet cleaning method.
  • Use wet cleaning for oily or grease-like contamination – Use a cleaning cloth or reel cleaner that is slightly wetted by a special cleaning liquid (no IPA)—why no IPA? Using 99+% IPA is by far the most common method used.  If it is not suitable, we should explain why.  What “special cleaning liquid” would be recommended. The liquid will dissolve the contaminant and prevent static charging of the connector end face, which results in a cleaner end face over time because fewer dust particles will be attracted. Also, the cleaning liquid won’t leave any residue when it evaporates.

After every cleaning step, check the connector by using a microscope with identical conditions: magnification, light settings, etc. If you still see a contaminant on the end face, repeat the cleaning step. If you started with dry cleaning, now use cleaning fluid to remove the contamination.

As you repeat the cleaning action, you can gradually increase the pressure you apply. Always start with gentle pressure to remove small debris such as loose polishing particles without scratching the surface. If necessary, other “sticky” contaminants can be removed using cleaning fluid and moderate pressure.

The art of cleaning during the installation process

When a fiber-optic network is installed, a specific installation routine must be followed in order to have a quick and error-free operational network. It’s helping to keep this phrase in mind: “First time right.”

Before a connector is patched, use a microscope to inspect the complete ferrule end face. You may expect that this connector passed all tests, had a clean end face, and was capped with a dust cap before the fiber optic cable assembly was packaged and shipped. In addition, after removing the cap in the field, you should expect to see some particles that came loose during transportation and handling.

It’s critical to apply the following cleaning techniques during installation:

  1. Unpack the patch cord, uncap it, and inspect the tip of the connector with a microscope. If the connector is not clean, carefully clean it with a dry cloth or reel cleaner. Check again and repeat until clean, eventually using the wet method, if necessary.
  2. Before patching, you must check all adapter ports for contaminants. If you see contamination, use a 1.25mm or 2.5mm dry swab to clean the end face. You can use the dry or wet method to clean the end face, depending on the contaminant. Inspect again. If BOTH connectors are clean – the connector in your hand and the mated connector – then you can install the connector. If the connector in the rack is contaminated, it can transfer debris, oil, or another contaminant to the pristine connector in your hand. This could result in a faulty connection in the field, which can be difficult and expensive to repair. For mated pairs of connectors, follow the rule to clean in pairs and do not clean one end insert and then take out the other end and clean. The rule is for situations when the other end that is mounted cannot be inspected (example: test equipment connector interface).  A final note: Be sure to read the cleaning instructions when a transceiver port needs to be cleaned.

Cleaning tips and tricks

The following tips apply to both “fields”: the fiber optic cable assembly manufacturing process and the installation process.

  • Start by washing your hands with a mild soap. Thoroughly rinse off the soap and dry your hands. Don’t apply any type of moisturizer or hand lotion, since this will contaminate the connector end face.
  • Don’t use latex gloves. They contain more oil and dirt contaminants than your clean hands.
  • Always inspect the connector first! Then determine the cleaning action. Inspect the connector after cleaning and repeat cleaning steps, as necessary.
  • Be careful when handling the cloth, wipe, or swab. Mishandling can lead to cross-contamination.
  • Don’t reuse cleaning materials. Any contaminants on the material can be transferred to the next connector, which can catastrophically damage that connector’s optical fiber. Don’t try to save a penny and, as a result, destroy a $10 patch cord or $500 patch cord!
  • When applying a wet cleaning action, use a special cleaning fluid. This specially designed fluid leaves no residue, evaporates quickly, does not statically charge the connector during cleaning, dissolves grease and oil-based contamination, and is not flammable.
  • Never use isopropyl alcohol (IPA)! It doesn’t offer the specific properties noted above, and it can turn your connector into a dust magnet. Should explain more, as this is by far the most common method. I believe some people use air de-ionizers, or something like that, at the cleaning stations, specifically to discharge any built-up static charge on the end-face.
  • When cleaning the end of a connector, be sure to also check the mated adapter or patch cord. When a clean connector is patched into a contaminated adapter, the contaminant is transferred. Carefully inspect both ends, clean as necessary, and check again. After everything is clean, you can make the patch. Now you can be sure the optical signal isn’t influenced by any contamination because both end faces are pristine.

In conclusion: Think “First time right”

When it comes to cleaning fiber optic connectors, it’s critical to take time to get it right. Carefully follow the specific cleaning techniques explained in this article during cable assembly production and installation. Good cleaning techniques will help to ensure your pristine connectors will make a good optical connection.





Additional resources from the FOC team include:

Do you have a specific issue regarding contamination or cleaning?

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