By Carlos Mora
The Importance of Connector End-Face Cleaning
The Importance of Connector End-Face Cleaning
Some years ago, NTT Advanced Technology performed a study to review what were the causes for which networks failed. The result, 98 percent of installers and 80 percent of network owners reported that fiber connector contamination was the greatest cause of network failure.
On the other hand we have Cisco, where in their “Inspection and Cleaning Procedures for Fiber-Optic Connections” mentions that “any contamination in the fiber connection can cause failure of the component or failure of the whole system” (1) and that “even microscopic dust particles can cause a variety of problems for optical connections” (1)
Additionally, in the SIGCOMM (Association for Computing Machinery's Special Interest Group) conferences in 2017, published a white paper regarding the “Root Causes for Packet Corruption” reporting that the connector contamination contributes from 17 percent to 57 percent for the packet corruption.
The previous information is more than a confirmation of what any installer is already aware of, the importance of cleaning the connector end face, but also at the same time validates the struggle the everyone knows, the desire to reach clean connectivity.
When the connector end face is clean, we will have no issues transmitting the light from one point to another. However when we have dirt, or any particle that can cause contamination present in the end face of our connectors, we will see an impact of the amount of light being transmitted, meaning a degradation of the signal or even a full link failure, that will be recognizable by the presence of strong levels of back reflection and insertion loss.
According to Cisco, “a 1 micrometer particle can block up to 1 percent of the light, generating 0.05 db loss” (1), imagine now what would happen to a single-mode fiber if a 9 micrometer particle is present, it could block the entire fiber core.
Among the different sources of contamination we can find:
- Dirt and dust. Where the air or the environment in which we are working can bring those particles to contaminate the end face.
- Dirty tools and test equipment. Imagine you are working on the field and you are cleaning your connector with a scope that hasn’t received the right maintenance, you will be bringing more contaminants to the connector.
- Residual contamination like skin oil and hand lotion that may occur during product handling.
- Ferrule cleaners, when adding liquids to clean the ferrule, but not properly removing the residues.
- Dust caps. Even when the name gives the idea that they can prevent dust getting in contact with the connector end face, this actually may work in the opposite way depending on the handling and the dust cap manufacturing process, where even some small plastic particles can get stuck inside of the cap. Dust caps are only effective to prevent scratches but not to keep particles away from the end face. Another type of contamination related to the dust caps is off gassing. Due to the quality of the plastics used for the dust cap manufacture, after the exposure to temperature and time during transportation or stock, gases can be released and “condensate” and dry in the end face of the ferrule, generating residues that will impact the performance of the connector. Finally, we also have an additional source of contamination due to the dust cap, called skiving. This is nothing more than the friction originated by the contact of the ceramic of the ferrule and the plastic of the dust cap; some plastic will be removed from the inside of the dust cap, generating debris that will get attached to the end face.
Light scattering can be identified by the presence of strong back reflections and attenuation, while the permanent damage can be related to pits and scratches in the connector end face.
The root causes for both light scattering and permanent damage have their origin during the connector mating:
- Particle migration. This root cause will affect the transmission of light. According to Fluke Networks “When the connector is unplugged and replugged, particles can move from a spot where they’re not a problem to one where they are” (3), in addition, JDSU (VIAVI) mentions that “Each time the connectors are mated, particles around the core are displaced, causing them to migrate and spread across the fiber surface.” (4)
- Air gaps or misalignment. JDSU (VIAVI) also mentions that large particles can create barriers or air gaps that prevent physical contact between the ferrules (5)
- Particle multiplication. JDSU (VIAVI) mentions that particles larger than 5 microns tend to explode and multiply upon mating, which will generate the creation of smaller particles that may cause further issues, not only light blockage but also permanent damage of the end face. (5)
Now that we have understood what are the sources of contamination and the impact of the contaminants on the connector end face, let‘s give a look to the most representative standard used every time we talk about the inspection of the end face, I am referring to IEC 61300-3-35.
The current version of the standard is the second edition from June 2015, and the standard defines itself as the “Methods for assessing the end-face quality of a polished fiber optic connector” (6). However, it is important to mention that the standard, in it’s procedure, highlights that “Inspection for cleanliness should take place prior to the inspection of the polished end faces” (6). Here it is important to mention that IEC is a good reference for analysing the end face, however, it is not a standard for cleaning end faces.
IEC defines four different areas to focus on for the end-face assessment: the core, cladding, epoxy ring, and contact. Important to mention, the size of those areas will vary depending on the fiber type, SMF or MMF:
However, the zones A to D represent only a small percentage of the total ferrule area.
Let’s take as an example an LC connector with a diameter of 1.25 mm, the zones A to D specified by IEC represent only 4 percent of the total ferrule diameter, this means that there is 96 percent of the area that is not covered by the standard, let‘s call this new area “zone X.”
In addition, for future revisions, IEC is looking to eliminate zones C and D from the standard, this means that now, in the same LC example, we will be only looking into a 1 percent of the total ferrule area, while the “zone X” will represent now 99 percent of the area, meaning 99 percent of the ferrule will be unattended.
This change will happen because currently for the multifiber products within a rectangular ferrule, this is referring to an MPO connector, the standard just refers to zone A and B for testing.
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”.
From all of this we can agree on the importance of having clean connectors when performing any installation in the data center.
When cleaning in the field, we can usually refer to two different methods:
- Dry cleaning. Cleaning pens or clickers are cleaning devices where the end face of a connector is wiped against a dry cleaning cloth. Clickers will be mostly used to clean patch panels and ports, but certainly dry cleaning will not be effective in the presence of grease/oil contaminants.
- Wet/Wet-to-dry cleaning. This occurs when the connector end face is wiped against a wet area (using a solvent) and then onto a dry area to remove the excess of solvent. However, this method, if not performed correctly or not using the right materials, may create static charges that will contribute to contamination of the connector ferrule.
These methods are extremely useful when cleaning in the field, and will assess the zones defined by IEC. However, we will still see poor-to-no cleaning in “zone X”, that may lead to debris migration into other zones, particle multiplication, and performance issues.
The truth is that there is no feasible way of getting to a completely pristine connector in the field. As mentioned previously, when looking into the different sources of contamination, even scopes can introduce and move microscopic dirt and debris on the connector end face making your connection fail to meet the link-loss standards.
In summary, cleaning is extremely important, the contamination of the connector end face is the main cause for network failures associated with connectivity. The presence of contaminants in the connector end face will have a direct impact in the performance of the link, causing signal degradation, that will be identifiable due to the presence of strong insertion loss and back reflection, plus the risk of causing also permanent damage in the end face.
IEC 61300-3-35 – Edition 2.0, 2015-06.