This presentation explains the special circumstances of military (hardened) fiber optic connectors and suggests specific tools and procedures for cleaning these devices.
This presentation documents the optimal technique to use when cleaning MT connectors and ARINC 801 connectors used on many fiber optic networks. It also shows they numerous types of contamination found on these connectors and explains the sources of those contaminates.
Here are some best practices for cleaning fiber optic connectors.
With the increase in network data rates, it it is increasingly important to ensure that all fiber optic connectors are cleaned before mating. This means that both sides of a connector are inspected and cleaned before making the connection. This applies to test equipment and test jumpers as well as network components. New connectors must be inspected and cleaned as well. Cleaning and inspecting every connection every time is your best assurance of a reliable optical network.
Please note that it is important to differentiate between contamination on an end-face versus a defect embedded into the surface of the end-face. In some cleaning process specifications, it instructs installers to notice if a defect/contaminant moves on the surface of the end-face. If it moves, it’s contamination. But in some cases a mark that appears as a contaminant may actually be a defect in the surface of the glass or ferrule. In these cases (non-movable defects), you do not have to worry about a potential migration of the contamination toward the core area causing system failure in the future.
Use of Wipes and/or Cleaning Cassettes
Fabric and/or composite material wipes provide combined mechanical action and absorbency to remove contamination. Wipes should be used with a resilient pad in order to avoid potential scratching of the connector end-face. This is appropriate for cleaning connectors with exposed ferrules or termini but cannot be used to clean connector end-faces within alignment sleeves. The wipe should be constructed of material that is lint free and non-debris producing during the cleaning process.
Installers should note that dry wipes leave a static charge on the end-face of the connector which thereafter attracts particulate contamination. Therefore, it is recommended that you use a static-dissipative cleaning fluid with a dry wipe to eliminate this condition.
Techniques for Cleaning with Wipes or Cleaning Cassettes
As mentioned above, use a lint-free, non-debris generating wipe with a static dissipative cleaning fluid. Dampen a portion of the wipe with the fluid, place the connector end-face into the damp area of the wipe and draw the connector into the dry area of the wipe. A physical wipe of 2 — 5 cm is sufficient. This may be repeated in a different area of the wipe if desired, however 1 or 2 strokes is sufficient for most common contaminants.
Upon inspection, if the connector is still dirty after the first cleaning, repeat the process. Do not attempt more than three cleanings. Perhaps slightly more pressure on the connector to increase the mechanical action will enhance cleaning. If the connector is still not clean and the contamination has not moved, it is non-removable contamination. Depending on the location and size of the contamination (See Tables 1 and 2, below) the installer may have to reject the connector.
Swabs or Port Cleaning Devices
Using purpose-built swabs or mechanical port cleaning devices provides excellent mechanical action and high absorbency of any contamination. However, since a port is very confined and the mechanical motion is limited, it is recommended that the “wet/dry” cleaning process be utilized for cleaning connector end-faces within alignment sleeves. A static-dissipative cleaning fluid adds chemical action to the cleaning process and eliminates any residual static charge on the connector. Ensure that the cleaning end of the swab or the port cleaning device is lint-free, non-debris generating material.
Select a swab or port cleaning device made for the size connector you are cleaning. Do not touch or contaminate the cleaning end of the swab or the port cleaning device. Dampen the swab or port cleaning device with a static-dissipative cleaning fluid. The swab or port cleaning device should be damp, but not wet. (The process is analogous to wiping a smooth surface with a sponge. A damp sponge will pick up contaminates, whereas a wet sponge will only spread them around.) If you use a very fast-drying cleaning fluid, then follow-up the cleaning with a dry swab.
When Using Swabs
Place the dampened cleaning end of the swab into the port and rotate the swab while applying some pressure to the connector end-face. Usually pushing so that the compression spring in the connector is slightly activated is ideal for 2.5mm connectors. Rotating the swab 6 —12 times is sufficient. The swab should only be used once and then disposed.
When cleaning angled polished connectors —APC connectors are typically color coded with a green connector housing or bulkhead adaptor— a turn back and forth rotation may help the swab end-face conform to the 8 degree angle. Thereby cleaning the entire surface of the connector end-face. If you used a very fast-drying cleaning fluid, then you are now ready to inspect. If not, repeat the above process with a dry swab.
When Using Port Cleaning Devices
Insert the solvent-dampened device into the alignment sleeve and activate the cleaner by either by pushing the device or by pressing on a button on the device. To accomplish the dry portion of the cleaning process, an additional activation of the device assures that any excess solvent is removed.
Upon inspection, if the connector is not clean after the first cleaning, repeat the process. If the connector is still not clean and contamination has not moved, it is a non-removable contamination. Depending on the location and size of the contamination (See Tables below) the installer should pass or reject use of the connector.
Notes about Cleaning Fluids
The fluids used to clean fiber optics should be fast-drying, static-dissipative and residue-free. Many solvents are flammable and/or considered hazardous materials, increasing the cost of shipment and storage of the solvent. However, there are cleaning fluids available that are non-flammable, non-hazardous and packaged so that shipping requires no additional fees or paperwork or costs.
Historically, 99% pure isopropyl alcohol (IPA) is used to clean. However, IPA is easily contaminated. IPA is hygroscopic and absorbs moisture from the atmosphere including any contaminants present, potentially leaving a haze on the connector end-face. This is a problem, especially with higher power laser networks. In addition, IPA is flammable and a hazardous material. Typically IPA must be repackaged for use and is therefore very subject to contamination.
Also, it is important to select a cleaning fluid that is compatible with the cleaning wipe, swab, or device. You do not want a cleaning fluid that dissolves the glue used in the wipe and leave additional contamination.
Don not clean connector end-faces with “canned air”.
Do not repackage cleaning wipes, swabs, cassettes, or port cleaning devices.
Do not repackage cleaning fluids as it leads to cross-contamination.
Use fast-drying cleaning fluids to clean (flush/rinse) inspection or test equipment adaptor caps. These adaptors are also sources of contamination in the optic network.
Table 1: Single Mode Connector Acceptance Criteria
|Zone||Description||Diameter||Allowed Defects||Allowed Scratches|
Table 2: Multi-Mode Connector Acceptance Criteria
|Zone||Description||Diameter||Allowed Defects||Allowed Scratches|
None >5 um
|5 < 3um
None > 5um
Zones are concentric circles about the center of the fiber in the connector end-face.
Defects may include non-removable contaminants.
Size of defects is defined as its widest dimension.
Size of a scratch is defined as its width, not its length
Why Clean Fiber Optic End-Faces?
Dirty connectors are the single most common reason for fiber optic network failures. Probably the most important items in a Fiber Optic Technician’s tool kit are the cleaning supplies, because nearly 50% of the failures he will encounter can be remedied with proper cleaning.
How Does Contamination Cause Network Problems?
First, if contamination blocks or partially blocks the light path then less light can pass through the connection. This decrease in light amounts to a decrease in signal strength, which may result in data errors.
The second way that contamination can cause a problem is if the contamination keeps the connector end faces from physically contacting one another. If this happens the Return Loss (RL) or “Back Reflection” increases which can have a devastating impact on the network.
How Does a Connector Become Contaminated?
In most cases, mated fiber optic connectors are not likely to become contaminated unless there is a clearly destructive event like a fire, flood or earthquake. Therefore, most connector end faces become contaminated when they are left un-mated (exposed) or handled by humans during deployment, testing or rerouting.
When Must Connectors Be Cleaned?
Every connector end-face that touches the network must be cleaned each time it is attached. Also, every port into which a connector is placed must be cleaned properly. This includes, test equipment and associated devices such as test jumpers, fiber boxes and attenuators as well as installation of new jumpers.
A Close Look at the Cleaning Process
Whether cleaning dishes, cars, windows or floors, the procedures are similar. For example, dishes. Remove any remaining food (now considered contamination) from the plate, wash the plate with detergent and a sponge, rinse the plate with hot water and then dry it with a clean dry towel. What really happens during those four steps?
Consider washing a car. Wet the car to rinse off large contaminates that might mar the surface. Take soapy water (the solvent) and apply it to the surface of the car with a “clean” sponge or soft rag. The wiping with the sponge or rag applies mechanical action to loosen the contamination from the surface.
Actually, much of the dirt is left in suspension in the soapy water on the surface of the car. That is why rinsing the soapy water off right away is important – so that contaminants, dirt, will not be re-deposited on the car. This rinse allows the loose contaminants to wash away. Then dry the car with a clean towel or chamois so that contaminants in the rinse water are not left on the surface. “Water spots” from dissolved minerals or other contaminants can spoil the appearance of the car.
What are the similarities in these cleaning processes?
- Gross cleaning to remove large contaminants.
- Use of solvents/soaps combined with mechanical action to clean the surface.
- Removal of the contaminants from the area (the rinse).
- Purity of the rinse and the ability of materials to absorb solvents and contaminants (chamois or towels).
A Quick Look at Familiar Cleaning Processes:
|Car||Dishes||Windows||Floors||Spill on floor|
|1||Gross contamination removal||Wet with water from hose||wet/rinse with water||Usually N/A except to remove cobwebs.||Sweep||Remove glass|
|2||Loosen contamination||Wash with soap and sponge||Wash with soap and water with sponge||Spray on solvent, wash with paper towel||Wash with mop and soapy water.||Use towel to absorb|
with water from hose
|Rinse with clean water||Wipe with solvent damp paper towel||Rinse with mop and clean water||Use towel to absorb|
|4||Assure no contamination left on surface||Dry with chamois||Dry with clean towel||Wipe with clean dry paper towel||Wipe with damp mop and leave to dry||Use clean towel to wipe dry|
What Happens During the Cleaning Processes:
|1||Gross contamination removal||Usually some form of mechanical action (moving air, moving water, brushing or wiping)|
|2||Loosen contamination||Chemical action of solvent combined with mechanical action of a wipe used together, or just the mechanical action of a wipe|
|3||Remove loosened contamination||Flush contamination with pure solvent rinse or use an absorbent wipe to remove contamination|
|4||Assure no contamination left on surface||Use a clean absorbent wipe to remove any remaining contamination on the surface|
Essentially, ideal cleaning results are dependent on mechanical action and chemical action to loosen the contamination. It also depends on the availability of a pure rinsing fluid to flush the contaminant away and a clean highly absorbent material to remove the contaminants from the surface to be cleaned.
Cleaning Fiber Optic Connectors
Now apply the above to cleaning fiber optic connectors. Remember, the end-face of the connector is typically ceramic and glass, which have been highly polished. Therefore, it is not likely that contaminants would penetrate the surface. However, ceramic and glass are excellent electrical insulators and can therefore hold an electric charge that can attract and hold very small particulate. And since there is concern about micron-sized contaminants, take the ionic bonds into consideration.
Also, consider the constraints under which the connector end-face is cleaned. It is certainly easier to clean an exposed connector end-face on the end of a patch cord than to clean an end-face hidden within an alignment sleeve. Wipe the connector end-face of a jumper with a lint free wipe repeatedly and if it does not become clean, dampen the wipe with solvent and continue the process.
However, when cleaning an end-face within an alignment sleeve, the ability to wipe is severely limited. Typically it is limited to the surface area at the end of a swab (which becomes very small with a small form factor connectors such as LC’s or MU’s). Therefore it is important to maximize the mechanical action and absorbency of the swab end-face.
The Optimal Cleaning Process for Fiber Optic Connectors
Let’s first look at cleaning exposed connector end-faces. Experience shows that wiping the connector end-face with a “lint free” absorbent material typically removes most surface contaminants. The material should be backed with a resilient pad (much like the palm of your hand) so that the material conforms to the end-face geometry and the end-face will not be damaged by any harsh contaminate on a hard surface. In cases where the wiping alone does not sufficiently clean, add solvent to the wipe. In this way both chemical and mechanical action is applied to the cleaning. However, the solvent used must be pure, and not leave a residue. The solvent should also be electrically conductive so that it can dissipate any electrical charge that may be ”holding” particulate on the end-face surface.
Cleaning Inside an Alignment Sleeve
Now consider a connector end-face or lens within an alignment sleeve. The ability to wipe is very limited. It is virtually impossible to provide the absorption and mechanical action applied to an exposed connector. One would have to use numerable swabs to achieve the surface area of one wipe of an exposed connector on a lint free wipe. Therefore, the careful choice of a clean lint free, highly absorbent cleaning tip that provides good mechanical action and conforms to the end-face geometry is necessary.
Also, the addition of chemical action (solvents) is advised. With the proper solvent, less mechanical action is required. However, the purity, absorbency and cleaning properties of the cleaning stick as well as the purity, volatility and cleaning properties of the solvent become key factors in selecting a cleaning process. To clean a connector end-face within an alignment sleeve, the solvent must be very pure and highly volatile and the cleaning tip must be clean lint-free, highly absorbent, provide excellent mechanical action and conform to the end-face.
Cleaning Fiber Optic Connector End-Faces:
|Exposed connector end- faces||Connector end-faces within alignment sleeves|
|1||Gross contamination removal||Usually some mechanical action (blowing air, spraying water, etc)||N/A||Canned air|
|2||Loosen contamination||Mechanical and/or chemical action: Wiping or solvent or both||Wipe with an
|Wipe with an absorbent lint free cleaning tip with solvent|
|3||Remove loosened contamination||Absorption of contamination with a material||Wipe with an
|Wipe with an absorbent lint free cleaning tip with solvent|
|4||Assure no contamination left on surface||Wipe with lint free absorbent material, rinse with ultra pure solvent||Wipe with an
|Wipe with an absorbent lint free cleaning tip with solvent|
Choice of Cleaning Materials
The first rule of cleaning materials is to do no harm. Wipes or swabs should be clean and non-abrasive so that they cannot damage the end-face of connectors. Likewise, solvents must be materials compatible so that surrounding components will not be damaged. Now let’s take a closer look at wipes swabs and solvents.
Choice of Wipes:
Carefully consider what material to choose for wiping the exposed connector end-faces. The material should be clean and lint free. A tee shirt does not fill this requirement. Remember, these are micron-sized contaminants requiring 200x magnification to view. Therefore, the wipe must be really clean, lint free and absorbent. The wipe provides mechanical action to loosen the contamination and also allows absorption to remove the contaminants from the surface.
Also be careful about the wipe location. Wipe on a resilient surface so that the wipe conforms to the end-face geometry of the connector and so that any hard contaminate that may be lodged behind the wipe will not protrude through the wipe and scratch the end-face permanently damaging it.
Choice of Swabs:
Swabs are typically used to clean connector end-faces within alignment sleeves. Like wipes, the cleaning tips must be clean, lint free, and highly absorbent in order to absorb as much contamination as possible. Also, since swabs are frequently used with solvents, the construction materials of the cleaning stick must be compatible with the solvent. One would not want the glue used to attach material to a swab dissolved by the solvent and left on the end-face of the connector.
Choice of Solvents:
When cleaning fiber optic connector end-faces with a solvent there are several issues that must be in mind. First, the solvent should not contain any water, detergents or surfactants. These materials leave residues on the surface. The ideal solvent is fast drying, leaves no residue, dissolves oils and water-soluble oils, and is conductive to dissipate ionic bonds. It should also have excellent materials compatibility so that it will not attack surrounding components. The drying speed (volatility) of the solvent is particularly important. A slow-drying solvent wicks within the slit of the alignment sleeve and other mating surfaces only to weep back out later (up to several minutes later) and wet the connector end-face.
IPA – Why Use It?
There are many disadvantages to using IPA to clean fiber optic connectors. Many older specifications recommend reagent grade IPA. Reagent IPA is 99% pure IPA. This grade of alcohol is not readily available. Most drug stores sell rubbing alcohol which is only about 60% IPA. Some higher grades range up to 91% IPA. The real problem with IPA as a cleaner is that it is infinitely hygroscopic. That is, IPA infinitely absorbs water from the surrounding air until it completely dilutes itself.
Therefore, it is next to impossible to keep IPA pure. As soon as the technician opens the bottle, the IPA begins to dilute. The issue with this dilution process is that the water it absorbs from the air has contaminants dissolved in it. These contaminants end up on the connector end face after cleaning. IPA leaves a “haze” on the end-face of a connector that can become literally “baked” onto the glass by high-powered lasers in long-haul systems if not wiped away immediately. Each subsequent cleaning adds to the “haze” and increases insertion loss for the system. This haze is only removed by re-polishing the connector end-face. Also, when cleaning within alignment sleeves, IPA does not dry fast and will likely re-contaminate a cleaned connector.
Consider Cleaning Fluid Safety
Another problem with IPA is that it is flammable and considered hazardous material. It cannot legally be transported without special manifests and HAZMAT markings. Therefore, in many cases the technician cannot take the cleaner with them to the job site. Also there are increased liabilities carrying flammable liquids for any employee; something every employer must consider.
Furthermore, IPA is a 100% Volatile Organic Compound (VOC). Most environmental groups are attempting to reduce the emissions of VOCs into the atmosphere. VOCs contribute in the formation of low-level (ground level) ozone and smog, which contributes to human health risks.
There are fiber optic cleaning fluids which address these issues for cleaning connector end-faces. Chemically, they are HFCs (Hydroflourocarbons) and HFEs (Hydroflouroethers). These fluids are fast drying, non-flammable, and not highly hygroscopic, like IPA.
Sticklers Products Get the Job Done
MicroCare Corporation has developed a line of cleaning products for fiber optics industry. These Sticklers™ products address the cleaning problems of both exposed connector end-faces and those within alignment sleeves.
Sticklers™ Fiber Optic Splice & Connector Cleaner is a very fast drying fluid that dries without a residue. This speeds up cleaning time. It is perfect for cleaning within alignment sleeves. It is an excellent cleaner and has exceptional material compatibility. This product is non-flammable, non-hazardous, non-regulated.
CleanStixx™ Connector Cleaning Sticks feature a high purity, sintered polymer material providing a clean fibrous, lint free, highly absorbent cleaning surface. These products come in various sizes for virtually any fiber optic connector. There are no binders or glues used in these cleaning sticks. When dampened with a cleaning fluid, the cleaning tip’s capillary action draws the contamination from the end-face into the stick tip.
Sticklers CleanWipes are highly absorbent lint free wipes ideal for cleaning exposed connector end-faces. The small, 2″ x 4″ wipes come in a box to keep them clean and ready for use.
Some Things to Remember:
- Every connector end-face that touches the network must be cleaned each time it is attached.
- Every port into which a connector is placed must be cleaned. This includes, test equipment, and associated devices such as test jumpers and fiber boxes.
- Ideal cleaning results depend on mechanical action and chemical action to loosen the contamination. In addition, the availability of a pure rinsing fluid to flush the contaminant away and a clean highly absorbent material to remove the contaminants from the surface to be cleaned is important.
- Cleaning materials must do no harm.
- Fiber optic cleaning materials must be clean, lint free and highly absorbent.
- IPA is not the best cleaner.
- Very fast drying cleaning fluids are necessary for cleaning connector end-faces within alignment sleeves.
- Always check the material compatibility of fiber optic cleaning fluids.
When clean fiber optic termini are undisturbed the optical path is preserved for years. However, during installation, maintenance, reconfiguration and equipment upgrades, those pristine connector end-faces risk exposure to the environment. The fiber optic termini may become contaminated. It’s estimated that connection points are the source of about 70% of the optical network failures. And 70% of those failures are a result of simple contamination of the end-face. The author explores better ways to clean and inspect fiber optic termini, saving time and money in the process.
Fiber Optic is Growing
Over the past decades, the use of fiber optics throughout industry and our daily lives has seen a remarkable increase. High power laser energy routinely travels through fiber for precision cutting, marking and etching of surfaces in conditions and places previously not possible. High definition TV, internet gaming,
medical data imaging, financial services, cloud computing, smartphones, general commerce and social networking all have dramatically increased the
demand for bandwidth. All the elements of optical networking are experiencing increased demand for bandwidth and the utility it provides. Be it long haul, back haul, FTTX, WAN or LAN. But, while the technology and reliability of optical components has improved over the past decades, there still remains predictable system vulnerability at the points of interconnect.
An interconnect is the point of mating two fiber optic connectors, or the mating of a fiber optic connector with an optical device. It’s estimated that connection points are the source of about 70% of the optical network failures. And more than 70% of those failures are a result of connector end-face contamination. This is because the interconnect is the only point in the network where the core of the glass fiber carrying the optical signal comes in contact with contamination from the external environment.
Keep Connectors Clean
When in service, connectors mate and make physical contact at their end-face within an alignment sleeve. They hold in place with springs contained within the connectors. This ensures continued physical contact and preservation of the optical path. However, during installation, maintenance, rerouting, and equipment upgrades, disconnected connector end-faces face exposure to the environment. It’s at this time the end-face risks contamination. Either by accidental human contact, by contact with an unclean connector such as a test jumper, or by coming in contact with airborne contaminants.
Maintenance of the connector end-face is imperative for the fiber optic network to work correctly. It is an exacting job. The termini that create a connection must meet at an exact place. And the microscopic glass cores need to be perfectly aligned in order to have signal transmitted through the interconnect. In addition, the termini end-faces must be perfectly cleaned of all contaminants to ensure minimal signal loss. Thus, one of the most basic and important procedures for the maintenance of fiber optic networks is to clean the fiber optic termini.
Importance of Cleaning
Any contamination on the termini end-face can cause failure of an optical device or the network as a whole. Even microscopic particles on the end-faces can cause a variety of problems for optical connections. One of the biggest challenges of contamination is that it cannot be seen with the naked eye. One must use a specialized 200x or 400x inspection scope to determine the cleanliness of the end-face. It is critical to closely inspect the connector to confirm the particles and residue are completely eliminated. Thereby ensuring the interconnects perform to their full potential.
A dirty fiber optic end-face significantly degrades signal transmission and can even block the optical signal all together. Even if a stray particle is only on the ferrule edge of the end-face, it causes an air gap or misalignment in the termini between the glass cores. This can result in back reflections, instability in the network, signal attenuation or even a system shutdown. Another potential issue is a scratched surface as a result of dust particles trapped between two termini end-faces. What’s more, some fiber optic instruments such as those using high power Class IV lasers, generate a significant amount of heat, which, when in contact with contaminants can spark a surprisingly violent reaction or fire.
One of the biggest challenges in cleaning fiber optic termini is establishing a process that works consistently. Improvising a cleaning process will almost certainly lead to failure, as outlined above. The best advice is to inspect, clean, and inspect again. Repeat this process until you are absolutely sure both ends of the interconnect are completely clear of all contaminants. Spending time to clean it right the first time will save you time and money in the end.
Materials used to clean the end-faces must be perfectly-clean, otherwise you can easily make the end-face worse by adding contamination. It may be intuitive to wipe the end-face on your coveralls or a spare cloth. But under a fiber optic inspection scope, those items carry a surprising variety of contaminants that will soil the connector. Even briefly touching the termini with your finger will cause it to be significantly dirtied with skin oil. To clean properly and avoid
further contamination, make sure to always use a cleaning product that has been specifically engineered for cleaning fiber optics. It’s also a good practice to always wash your hands prior to using fiber optic cleaning materials. This avoids the transfer of skin oil onto otherwise pristine cleaning products.
There are two basic methods properly clean fiber optic termini. A high purity wipe for male connectors, and a specialty swab for female connectors. It’s important to note that while wipes work on almost all configurations of male connector termini, swabs are sized specifically for the type of connector being cleaned. Beware, a swab sized to clean an SC connector will not fit in a LC connector alignment sleeve. To achieve your goal of a perfectly clean termini end-face, swabs and wipes should always be used with a high purity fluid.
Three types of Contamination
In very general terms, contamination found on termini end-faces falls into three basic categories: particulates, oils and salts. Each requires specialized methods for proper removal. Particulates are solids, usually held on the end-face by electrostatic attraction. Even experienced technicians are surprised to learn that static attraction, increased by the mechanical action of a cleaning product, creates a triboelectric charge on the non-conductive termini end-face.
That triboelectric charge will actually attract dust particles like a magnet.
The best way to clean particulates is by dissipating the static charge that both attracts and holds them in place. Use a specialty cleaning fluid that actively dissipates static charges. A well-engineered cleaning fluid selectively dissolves oils found on the fiber end-face without damaging materials used to make the connector, its housing, or surrounding components. Salts, on the other hand, are not necessarily fully removed by cleaning fluids alone. While cleaning fluids may quickly dissolve oils and rinse away particulate, they frequently dry and leave a white residue that is very difficult to remove. The absorbency and mechanical action of a wipe or swab improves with the addition of a cleaning fluid. It helps to fully eliminate oils, particulates and salts that otherwise stay on the termini end-face.
Buyer beware, some cleaning products on the market leave the end-face dirtier than when you started. To avoid this situation, look for products that combine wipes and fluids engineered to work together to rid the termini end-face of particulates, oils and salts.
Avoid using aqueous (water based) cleaners or isopropyl alcohol (IPA), as both present significant limitations. Aqueous products dry slowly and, when used improperly, leave moisture on the end-face. In cold ambient temperatures, the moisture may actually freeze on the end-face or in the alignment sleeve. In extreme cases such as with high power lasers, if the moisture is not completely removed before the connectors mate in the sleeve, the laser-energized fiber instantly transforms the remaining liquid into vapor. This causes a small explosion through sudden expansion of the vapors.
IPA is typically comes in low purity grades and packaging simply not suitable for cleaning fiber. As a result IPA frequently leaves a hazy film behind when it dries. As with water-based cleaners, in extreme situations IPA may cause sudden vapor expansion problems or possibly ignite if left on a highly energized fiber end-face. Look for a fast drying, high-purity fluid formulated, packaged and labeled specifically for cleaning fiber optics.
Beware of Presaturated Wipes
High-purity cleaning fluids should always be used with both wipe and swab applications. But, beware of pre-saturated cleaning materials. Pre-saturated wipes and swabs often contain microscopic oily residues extracted from the plastic packaging. This then transfers to the end-face during the cleaning process. Instead, carefully apply a small amount of high purity cleaning fluid on a corner of a dry wipe or the tip of the swab. Then clean the fiber optic termini. A well-engineered cleaning fluid dissolves oils found on the end-face. It also helps eliminate the electrostatic charge generated as the applicator pulls out of its packaging or draws across the fiber end-face when cleaning.
Remember, microscopic amounts of contamination causes big problems on a termini end-face. Use care to not touch the area of the wipe or swab you will be using to clean with your finger or your clothing. Should you touch the area of the wipe or the tip of the swab with your finger or drop it on the ground, discard the wipe or swab and start over. Avoid reusing cleaning swabs and wipes because they transfer contamination onto the next connector. Once the cleaning process is complete, discard the wipe or swab. Then inspect the end-face to ensure they are contaminant-free.
Bottom Line: Performance Critical Cleaning
Our reliance on fiber optics continues to grow. It is imperative to clean interconnect end-faces perfectly the first time around with the right products, the right way. Fiber optic service professionals can’t afford to leave behind end-face contamination which results in poor network performance and costly callbacks. Use the correct cleaning products and closely inspect the end-face to avoid these costly mistakes. Investing the time, energy and money into
the cleaning process at the beginning ends up saving you in the end.
Improperly cleaned fiber end faces have operational and financial implications, but can be avoided.
Every cable assembly manufacturer strives to produce pristine ferrule end faces with zero defects. In the real world, this lofty goal is impossible to achieve. Even the best cable assembly manufacturers have an occasional scratch or pit on the ferrule end face. The purpose of this article is to review the current operational and financial implications of improper cleaning of end faces, and to suggest improved techniques that will reduce operating costs and improve network reliability.
The Industry Standard
As a matter of background, the International Electrotechnical Commission (IEC) published the fiber end face specification 61300-3-35. This standard was developed to guide the fiber-optic industry in determining what kind of defects could be on the ferrule end face with no negative performance impact.
Digital ferrule scopes are commonly used in production and by field installers to inspect ferrule surface quality and comply with this specification. Most digital scopes employ automated, software-driven algorithms to accurately compute the size, area, and location of end face defects. This is an important advancement for the industry; every installer should have this type of gear available to them in the field.
The reason for this concern is that the location of defects relative to the center of the fiber core—the contact zone—is the critical measurement. A 1-pm or 2-pm length can be the difference between having an end face that meets or fails the 61300-3-35 specifications. Even the most experienced operator cannot visually determine if a scratch is 5 pm or 6 pm in length. The use of a digital ferrule scope with automated analysis software set to the IEC 61300-3-35 standard eliminates human error in determining if a defect will negatively impact network performance.
Field installers have limited options for addressing permanent defects like pits and scratches on the ferrule end face. The vast majority of cable assembly manufacturers perform 100-percent optical testing, so it would be a rare occurrence to get a fiber cable assembly shipped from the factory out of spec.
The more common end face defect that field installers encounter is generally termed “debris.” Debris is dust, lint, plastic or ceramic particulate, fingerprint oils or a host of other contamination. The industry’s best practice is to remove all debris from both connector end faces using optical-grade cleaning materials before mating the connectors.
Inspect, Clean, Inspect
It is vitally important to inspect each end face after cleaning and before mating to ensure the debris is removed. At a minimum, failure to remove the debris will cause cross-contamination of the two ferrule end faces, disrupting the optical signal path. Particulate debris in the contact zone frequently causes scratches and pits on both connector end faces. This is the reason Section 5.3 of IEC 61300-3-35 advises installers to inspect the connector end face, clean the end face if necessary to remove contamination, and re-inspect the ferrule. The total inspection process, using a digital ferrule scope, takes less than five seconds for an accurate analysis. Importantly, most modern digital scopes also capture an image of the ferrule end face. This helps to document the condition of the end face and ensures the performance of the network.
Static Charge Problems
Dry particulate has a very sly manner of moving onto fiber end faces and causing network problems. The symptoms of the problem are perplexing. For example, an operator cleans and inspects an end face, and sees a pristine result. Then, the operator returns at a later date and finds troublesome dust particles on the end face. How can this happen?
The problem is the process, not the particulate. Dry-wiping cleaning is a common process used by well-intentioned installers. However, anytime two different materials rub together there is a transfer of surface electrons that creates a static charge. The technical term for this event is “triboelectric charging.” The contact friction from the wiping process creates a static charge on surfaces of both the connector and the wipe itself.
Dielectric materials like ceramic ferrules and composite MT ferrules are insulators, not conductors, and they will store the static charge. The voltage remains trapped indefinitely until a conductive path is created. Any debris residing inside the connector housing quickly becomes attracted to the ferrule end face and tightly bonds to that surface by what is known as electrostatic attraction (ESA).
Sources of Static
Static, as all forms of electricity, follows the path of lowest resistance. Static charge on an end face builds up to the highest levels to the apex of the end face. A common cause of static charge is using a dry wipe or swab to clean connectors in low-humidity environments. This causes particles attracted to the static to migrate toward the contact region of the ferule, where it causes the most problems. Common sources of static charge caused by contact friction in optical networks include the following.
- Dry-wipe cleaning
- Insertion of inspection scopes and test gear into adapters
- Connector mating
- Equipment cooling fans and fans in the HVAC system
Solving the Static Problem
Static charges on the end face attracts and holds particulate debris for days and even months. The debris remains bonded to the end face until the static charge finds a conductive path for it to dissipate. The introduction of a cleaning fluid creates that conductive path, making it easy to physically wipe the debris away. The most effective cleaning process to solve this problem is using an optical grade cleaning fluid. The liquid temporarily creates the conductive medium for the static to dissipate.
Cleaning at What Cost?
Cost implications of not cleaning contaminated end faces such as those described above can be very costly. Dirty connectors will slow data speeds and, in the worst case, bring a fiber network down. What will this cost?
The average cost of network downtime is approximately $8,000 per minute. Industries suffering the highest downtime cost included hospitality, public sector, transportation, and media organizations. Installation companies are investing large amounts of capital in the latest network testing gear and personnel training to meet project requirements and customer expectations. But for the networks to operate at their designed reliability, companies must use the proper cleaning tools.
Here’s another way to look at it: Labor costs account for 60 to 80 percent of fiber deployment expenses. The cost to roll a truck and crew back to a worksite to repair a network failure is typically around $250 to $500 per incident. Unfortunately, after spending huge sums on test equipment and training, many companies suddenly become overly frugal and choose the cheapest options instead of the most effective options when selecting the connector cleaning consumables to be used on the work site.
Invest in a Quality Cleaning Fluid
Isopropyl alcohol (IPA) and paper-based tissues are the lowest-cost options and most common cleaning consumables. Both are poor choices.
As a cleaning fluid, IPA has a major deficiency. It is hygroscopic. Meaning it attracts water molecules from the air even at low relative humidity. IPA packaged in containers that are not hermetically sealed can easily become contaminated by atmospheric moisture as well as the dust particles that float in the air. Dust particles floating in the air bond with water molecules and then absorbed into the IPA. After two or three days, the 99-percent IPA that was poured into the container is diluted with floater particles.
Alcohol is also highly flammable and has a high vapor pressure that makes it dangerous to use in areas where there are flames or sparks. Most alcohol-based cleaning solvents also are regulated hazardous materials and cannot easily be shipped by air.
Replacing IPA with a precision cleaning fluid engineered for optical device cleaning is a better option for cleaning fibers and connector end faces. Unlike IPA, high-quality fiber-optic cleaning fluids clean better, dry quickly, and do not leave a residue on the end face. To further minimize the risk of contamination, use a cleaning fluids packaged in a hermetically sealed, nonrefillable container. Cleaning fluids and packaging developed and tested specifically for cleaning fiber optics produce the best results.
Replace the Paper Wipes
Paper-based tissue wipes are cheap, but cause more problems than they solve. They have a low shearing strength, causing the fibers to separate easily as the operator wipes the ferrule end face. This deposits debris on the end face.
Some installers use pre-saturated alcohol wipes to clean fiber end faces and fibers for splicing. Pre-saturated wipes frequently become cross-contaminated. Plus, the cleaning fluid causes the packaging to break down over time. Temperature cycling accelerates degradation of the packaging material, which begins to leech into the cleaning fluid and contaminate the wipe.
Make sure to only use optical-grade, lint-free wipes that have high absorbency and high shearing strength. Reusing wipes and cleaning sticks will eventually cause problems related to cross-contamination.
Avoid using aqueous (water-based) cleaners. Aqueous cleaners are weak cleaners, slow to dry, and can leave moisture and streaks on the end face. Aqueous-based solutions are also susceptible to freezing in cold climates.
Make Better Cleaning Choices
Famed basketball coach John Wooden used to ask his players at the University of California Los Angeles, “If you don’t have time to do it right the first time, when are you going to have time to do it right?” Therefore, my final recommendation to installers is this. Pick the right cleaning materials made for cleaning optical connectors, and do it right the first time. Failure to heed this advice will cost you long term in callbacks, network downtime, and frustrated customers.