End-Face Cleaning is Crucial to Network Performance

NTT conducted a study a few years ago to examine the reasons why networks failed. As a result, 80% of network owners and 98% of installers said that fiber connector contamination was the main reason for network failure.

Cisco states that "even microscopic dust particles can cause a variety of problems for optical connections" and that "any contamination in the fiber connection can cause the failure of the component or failure of the whole system"

Similarly, a white paper on the "Root Reasons for Packet Corruption" said that connection contamination contributes between 17% and 57% to packet corruption.

The information shown above more than just confirms what every installer already knows—namely, the necessity of cleaning the connector end face—but it also serves as validation of the fight that everyone is aware of—the desire to achieve clean connectivity.

We won't experience any problems transferring the light from one location to another when the connector end face is spotless. The amount of light being transmitted will be affected by the presence of dirt or any other particle that can cause contamination on the end face of our connectors, leading to a deterioration of the signal or even a complete link failure, which will be discernible by the presence of high levels of back reflection and insertion loss.

Imagine what would happen to a single-mode fiber if a 9-micrometer particle was present; it could block the entire fiber core. A 1-micrometer particle can block up to 1 percent of the light, creating 0.05 dB loss".

We can identify a variety of causes of contamination, including:

Dust and dirt. Where such particles may be carried by air or the environment in which we are operating and contaminate the end face.

Dirty test instruments and devices. Assume you are cleaning your connector while working on the field with a scope that hasn't been properly maintained; you will be adding extra impurities to the connector. 

Residual contamination may happen when handling a product, such as skin oil and hand lotion. When adding solutions to clean the ferrule, ferrule cleaners often fail to completely remove any residues.

Dust cap. Although the name suggests that they can keep dust from coming into touch with the connector end face, depending on how they are handled and how the dust caps are made, even tiny plastic particles can become lodged within the cap, making them operate in the opposite manner. Dust caps are only useful at preventing scratches; they do not effectively block the end face from being polluted. Off-gassing from the dust caps is a different kind of pollution. Because of the polymers' high quality, gases may be released and "condensate" and dry on the end face of the ferrule during transportation or storage after exposure to temperature and time, leaving behind residues that will impact the performance of the connector.

Lastly, skiving, a different source of pollution brought on by the dust cap, is also present. A little amount of plastic will be taken from the interior of the dust cap as a result of friction between the ceramic of the ferrule and the plastic of the dust cap, creating debris that will become stuck to the end face.

Both light scattering and irreversible ferrule damage are potential effects of such impurities on the connector end face. Strong back reflections and attenuation are signs of light dispersion, whereas pits and scratches on the connector end face are indicators of irreversible damage.

Light scattering and lasting damage have their origins in the connection mating process.

Migration of particles. The transmission of light will be impacted by this primary cause. When the connection is disconnected and replugged, Particles might travel from a position where they're not a concern to one where they are." JDSU further states that "Each time the connectors are mated, particles surrounding the core are dislodged, causing them to migrate and disseminate throughout the fiber surface."

Air gaps or alignment. Large particles may form barriers or air gaps that inhibit direct contact between the ferrules, according to JDSU.

Multiplexing of particles. According to JDSU, particles large than 5 microns have a tendency to burst and multiply upon mating. This will result in the development of smaller particles that may create further problems, such as irreversible damage to the end face in addition to light obstruction. Now that we are aware of the sources of contamination and how they affect the connector end face, let's examine the most prevalent standard that is mentioned whenever we discuss the inspection of the end face—IEC 61300-3-35.

The current standard, which dates from June 2015 and describes itself as "Methods for measuring the end-face quality of a polished fiber optic connection," is the second edition. It is crucial to note that the process for the standard emphasizes that "Cleanliness inspection should be conducted prior to the examination of the polished end faces". However, it's critical to note that while IEC is a useful resource for end-face analysis, it is not a standard for end-face cleaning.

The core, cladding, epoxy ring, and contact are the four regions that the IEC specifies should be examined for the end-face examination. Important to note: According to the fiber type, SMF, and MMF, the size of the sections may change.

Yet, only a small portion of the overall ferrule area is included within zones A through D.

Consider an LC connection with a 1.25 mm diameter. The zones A through D described by IEC account for just 4% of the total ferrule diameter, leaving 96% of the region unaddressed by the standard, which we will refer to as "zone X."

In addition, IEC intends to remove zones C and D from the standard in the next versions. As a result, in the same LC example, we will no longer be examining more than 1% of the entire ferrule area, but rather 99% of it, which means that 99% of the ferrule will remain unattended.

This will change since the existing standard only mentions zone A and B for testing for multifiber goods contained in rectangular ferrules, which relates to MPO connectors.

With this change, there will be an increased risk of particle migration and spreading, which, as we have seen, is one of the root causes for light scattering; and unfortunately, even when scopes still will be able to show how clean our end face is within the zones defined by IEC, they will not show us what happens in the "zone X".

We can all conclude from all of this that while executing any installation in the data center, clean connections are essential.

Drying Cleaning. Cleaning pens or clickers are tools used to clean connector end faces by wiping them on dry cleaning cloths. Patch panels and ports will mostly be cleaned using clickers, however dry cleaning will undoubtedly fail if there are impurities like grease or oil present.

Wet/Wet-to-dry cleaning. This happens when the connector end face is wiped against a wet surface while using a solvent, and then the excess solvent is wiped off onto a dry location. The connection ferrule may get contaminated by static charges if this process is not carried out properly or the wrong materials are used.

These techniques will evaluate the zones specified by IEC and are very helpful while cleaning in the field. In "zone X," there will still be little to no cleaning, which might cause debris to move into other zones, particles to multiply, and performance problems. The reality is that there is no practical way to reach a perfectly clean connection in the field. As was already indicated, even scopes can introduce and transport tiny grit and particles onto the connector end face, causing your connection to fail to satisfy link-loss criteria.

In conclusion, cleaning is crucial since contamination of the connection end face is the major reason for connectivity-related network problems. Contaminants on the connector end face will directly affect how well the connection performs, resulting in signal deterioration that will be noticeable owing to the presence of high insertion loss and back reflection, as well as the possibility of inflicting irreversible damage to the end face.