Fiber Cleaning and Inspection Best Practices

Fiber Cleaning & Inspection
Best Practices

The ability of a test setup to measure fiber optic cables and components accurately is highly dependent on the quality and condition of the cables used. Connectors especially are susceptible to dirt or scratches on the fiber end face. These imperfections can cause excessive loss and prevent proper mating of connectors, all of which compromise the performance and results of the test. There are steps that operators can take for the prevention, detection, and correction of these issues.

Prevention: Dust Caps and SAVer Cables

The most effective way to protect connectors and equipment interfaces from dirt or damage is to keep them covered when not in use. OptoTest equipment ships with dust caps on all ports and it is strongly advised that you keep the dust caps and use them to cover any open ports. Cables also ship with dust caps and should be covered when they are not connected in a bulkhead.

An OP940 with dust caps on the source and detector ports

Besides covering ports when not in use, another prevention step for the front panel is to avoid excessive connections to it. SAVer cables are a great tool because launch cables mate to them rather than to the front panel directly. This is especially useful for test environments when the same equipment is used to test different connector types that require different launch cables in the setup. Should damage occur at the connector interface, the SAVer cable is more accessible for cleaning and repair than the internal connector.

image of Saver Cables
Sumix Manta microscope view

Detection: Inspecting

Prior to mating connectors to the test equipment or to each other, all end faces should be inspected to identify impurities or imperfections. Typically, the naked eye is not enough to detect these impurities so there are a number of handheld and benchtop tools available to help inspect connectors. Through our partnership with Sumix we are able to offer some of the best inspection and interferometer devices in the industry, including the very same ones that we use in house for our production needs.

Correction: Cleaning Tools

When dirt or damage is found on the end face of a connector, it is important to address the problem before that cable can be used as it could compromise other elements of the setup. The types of imperfections can range from surface dirt to deep scratches and must be dealt with accordingly.

Note that in addition to the connector surface, dirt can also enter the guide pin holes of MPO/MTP connectors and prevent proper mating. A brush cleaning tool can be used to dislodge dirt from these connectors.

For surface dirt, dry cleaning using a cleaning tool is sufficient. Alternatively, nonwowen dry cleanroom wipers like the TX604 from Texwipe® can be used. If the impurities do not come off by dry cleaning, like in the case of water spots or oily residue, deeper cleaning with alcohol and TX604 wipers is recommended.

Once a connector end face is cleaned of impurities, one of two things will happen: the connector will be deemed ready for use or the cleaning will expose deeper imperfections that must be addressed. Polishing is the next step to do away with pits or scratches on the connector surface. Polishing by hand is best for individual or small quantities of connectors. If multiple connectors require polishing there are machines that can do so at higher volumes, such as the Domaille polishers that we use in-house.

Any deeper scratches that are not fixed by polishing may require that the connector be re-terminated or the entire cable be replaced. These should be the last resort for addressing issues as they will likely require some level of re-calibration of the device in the case of internal connectors on test equipment.

FREQUENTLY ASKED QUESTIONS

Poor Insertion Loss or Return Loss Results?

Dirt or scratches on the connector end face, particularly on the core of the fiber, will impact insertion loss (IL) and return loss (RL). The imperfections will obstruct light from reaching the detector and will affect how and how much light is reflected back towards the source from the end of the fiber. 

Getting gainers?

Gainers occur when the detector reads more light during the measurement step than during the reference step. Conceptually speaking, mating a DUT to a launch cable results in loss as the light travels from one fiber core into the next, so detecting more light after the connectors are mated should not be possible. However, what if a spec of dirt obstructed the core of the launch cable end face during the reference step? And what if this spec of dirt was removed or dislodged before mating the launch cable and the DUT? This is precisely what can cause gainers. Inspect (and clean as needed) all connectors before every step of the test process to ensure optimal performance and consistency. 

Large reflection at the front panel?

If your test equipment is giving an error indicating that there is a large reflection at the front panel, it is likely that either the launch cable mated to the front panel, the internal connector, or both are dirty or damaged. Inspecting these connectors and performing any needed cleaning or repair should take care of the issue. 

I inspected and cleaned my connectors and I still have issues! What else could it be?

Sometimes connections have excessive loss without cleanliness of the end faces being the cause. Other setup details to look at include:

  • Cracked ceramic sleeves within the bulkhead (FC connectors). 
  • Misalignment within the mating adapter. This is especially true for APC connectors. Always be sure to confirm proper key alignment when mating. 
  • Dirt within guide pin holes (MPO/MTP connectors). 
  • Dirt or damage to the detector. Using a dust cap to protect the detector interface when not in use can help prevent this.