Over the years we have received many pieces of damaged test equipment, tech support calls, and bad looking traces with one thing in common: contaminated connectors. Cleaning fiber optic connectors isn’t optional it’s critical!   Over 80 percent of all issues in fiber optic networks can be traced back to contaminated or damaged connectors. In this paper we will concentrate on only the most useful information and tips that you can use in the field immediately.

The amount of information available on cleaning fiber optics connectors can be overwhelming to say the least. Cleaning connectors also happens to be one of the least exciting topics in all of fiber optics. But if we examine the disastrous effects of not cleaning connectors, it’s a lot easier to pay attention to this topic. Contaminated or damaged connectors cause high insertion loss values which steal power from the network. Contaminated connectors also create strong back reflections which will reduce the ORL values and ultimately create high Bit Error Rates which equate to information not reaching the intended destination. Contaminated connectors damage test equipment and any other equipment or cable they come in contact with. Contaminated connectors also produce inaccurate test result measurements.

Before we dive right into cleaning we need to address one specific question we get asked frequently. “When should I clean fiber optic connectors?” The correct answer is any time the connector is going to be installed. This means cleaning brand new patch cables right from the factory, connectors you have previously disconnected from equipment or racks and any connector you intend to connect to something. Do not assume the connector is clean even if you just disconnected it from an active system.

The word contamination is used very frequently to sum up a wide variety of possible soils that create dirty connectors which lead to damaged connectors. Possible soils that can create contamination include dirt, dust, skin oil, icky pic, solvent residues and other particles. Typically we break down soils or contaminants into two distinct groups, Ionic and Non Ionic. Ionic soils include skin oil, residues or any other soil that does not have the ability to bond with the ferrule. Ionic soils are easier to remove.   Non Ionic soils such as dirt, icky pic and oily soil or hand lotions can create a bond to ferrules through charged particles or molecular adhesion.   Non Ionic soils typically require some type of cleaning solution to be completely removed.

Now that we have defined our possible contamination sources it is important to discuss the microscopic scale we are working with. First be aware that the core of a Singlemode fiber is 9 microns. Nine microns is a difficult value to visualize but we like to compare it to a single red blood cell which is around 5-8 microns. Note that a human hair is approximate 80 microns in diameter and the naked human eye is only capable of seeing particles as small as 40 microns. These facts clearly indicate that a human is incapable of determining a clean connector without magnification of at least 200x.

Particle comparison can be taken one step further by investigating three categories of particles and their impact of connector mating. Different particle sizes will “react” differently when connectors are mated together.   First a 10 micron particle is quite large and will hold connector end faces apart or be crushed into smaller particle sizes. Either option is going to create poor connector performance as true physical contact can be inhibited.   Five micron particles tend to be crushed down to smaller particle sizes which can be worse than expected.   Particles smaller than five microns tend to get embedded in the end face of the connector which can create pits and scratches. These pits and scratches can cause damage to other connectors and produce inconsistent transmission performance especially when testing. Pits and scratches are permanent issues which typically require replacing connectors.

Several years ago the industry began to see an increase in disputes between customer and contractor regarding the condition of the connector end face. At that time the standards for cleaning were loose at best and required attention from standards organizations. Today the industry has a cleaning standard which contractors and customers can reference to resolve such disputes. The new standard IEC 61300-3-35 put forth a concept of inspection zones with each zone having specific criteria. The standard created four zones: the core, the cladding, the adhesive and the contact zone. Each zone has specific criteria which must be evaluated in order to meet the pass threshold.   This standard took much of the guesswork out of inspection and now many test equipment companies sell video microscopes with software packages which can perform an automated test and generate reports. Below is a more in-depth look at the zones and inspection criteria.

Particle Comparison

Inspection Zones

Inspection Zone Criteria

One of the most important aspects of cleaning connectors is to use the proper cleaning techniques. There are two basic cleaning techniques available which are very effective, dry cleaning and wet to dry cleaning.   Dry cleaning can be used for Ionic soils such as skin oil and certain Non-Ionic soils such as dust. However we should not consider dry cleaning to be the superior cleaning practice; it is simply the easiest.   Wet-to-dry cleaning is the superior option, which involves using a cleaning solution to loosen all types of contaminants then removing the solution and contaminants with a dry cleaning product. This technique is by far the best option for any technician, especially when a dry cleaning process leaves dust or pits. By using the wet-to-dry technique a technician can differentiate between pits and dust easily. Note any locations on the ferrule end face where a questionable pit exists. Clean the connector using the wet to dry technique and inspect the connector again. If the questionable pits are gone it was dust. If the pits remain repeat the process one more time to confirm pits actual exist. Document or replace any connectors that display pits and never plug that connector into test equipment. The pit will be transferred to the equipment ferrule during the first test sequence.

Connector cleaning products have become an industry all by themselves. With so many different options available today it can be difficult to pick the best option for your company. But let’s not try to determine the best right away; instead we can identify what not to use first. Paper towels, tissues, T-shirts or any other fabrics are typically not a good idea as they will leave behind lint. 99% Isopropyl alcohol has long been the solvent of choice for cleaning connectors, however it has one major flaw. 99% Isopropyl Alcohol does not like to stay at the 99% purity level. Isopropyl Alcohol likes to be around 70-80% purity level which means 20% of the product you are using is water or other contaminants. Water and other contaminants will not evaporate as quickly as alcohol and will leave a haze over the end face of the connector. This haze will increase insertion loss values with only minimal impact on reflectance. What results from this is a connector which fails an OTDR test as the insertion loss is high yet the reflectance is normal. This combination can be confusing for many technicians who have not experienced this before. Technicians should inspect this connector for rings of residue or discolored hazes around the fiber’s core and cladding area.

Now that we have established what not to use we will address what should be used. Please note that this list is not an-end-all-be-all list. The information presented is based on our experience with various products and we are suggesting the items which we find most effective for everyday use.

Wipes can be used for both wet and dry cleaning of ferrules or fiber preparation for splicing. While many options exist for wipes the most important criteria is that the wipe be low lint. This will reduce the likelihood of particles being introduced to the connector from the wipe. Common low lint wipe available almost anywhere in the market are Kim Wipes.

Another option for dry cleaning are cartridge cleaners. Cartridge cleaners are typically used for the dry clean portion of both dry and wet-to-dry cleaning techniques. An important aspect of the cartridge cleaners is the material which the cleaning cloth is made from. Polyester weaves have become very popular today as they are low lint and can be woven with other materials to produce a consistent cleaning media.

One final dry cleaning option that is very useful is One Click Cleaners. These units use a small wand style tip with a cleaning tape to clean through bulk head adapters. A specialized boot on the wand tip can also be used to clean patch cables.   These One Click Cleaners are very useful for cleaning test equipment as well.

As for cleaning solutions available in the market the options are plenty. Each manufacturer will have their own proprietary formula which they will market as superior to others brands based on a multitude of reasons including packaging, purity levels and price. The real concerns to any technician should be as follows:

How fast does the product evaporate while cleaning?

Products that evaporate slowly tend to leave residue behind, while extremely fast evaporation means you will use more of the product to complete the project.

What is the shelf life of this solution?

Certain products can diminish in purity over time as infrequent use causes air to be trapped inside container reducing the purity and solutions can react and absorb contaminants from the packaging such as low quality metal containers.

Finally, does this product have shipping restrictions?

Products with shipping restrictions can have slower delivery times along with higher deliver charges associated with Hazardous Material shipping restrictions.

Regardless of which cleaning products you choose, be sure to use them sparingly.   Over application of cleaning solutions is something that every technician is guilty of at least once in their life.   The issue with over application is not only incomplete evaporation but also cleaners applied to the side of the ferrule can actually wick towards the connection point after inspection and connection. A common example of over application can be seen below. Note the ring of solution around the fiber. This ring is actually an outline of the contact zone.

We have covered a lot material today, but remember that we have touched on only the most important points. If one desired to learn all there is to learn about cleaning, the road would definitely be long and full of different perspectives. Our final thought for this article is the simplest principle we teach all of our technicians before they head into the field to perform Fiber Characterization or other testing services. “You can clean connectors but if you don’t inspect the connector with a microscope how do you know it is actually clean? You don’t! Always inspect after cleaning.”

Over-application of solvent cleaner dried