Long ago in days of yore, like the 1970s, Bell Labs was busy perfecting the technologies to commercialise fiber optic communications. Peering into their crystal ball in the nascent years of the digital age, they could see a time in the not-to-distant future when all the copper wire in the world could not handle the volume of data that people would want to send over phone lines.
One of the issues with which they struggled was finding suitable ways to quickly, conveniently and consistently clean the delicate fiber optic connectors. They found very early on that even the slightest contamination on the end-faces significantly degraded the performance of their networks. The scientists at Bell Labs recommended using only 99% reagent grade isopropyl alcohol (also known as “IPA” and “rubbing alcohol”) for cleaning their fiber optic connectors.
They made this recommendation for two reasons: it was readily available on their workbenches, and it worked. It worked because the solvent provided additional chemical action to enhance the mechanical action provided by the cleaning device (the wipe or swab). Alcohol and other solvents also are very effective at softening, loosening and/or dissolving dried-on contaminants and particulate. In short, those clever engineers at Bell Labs proved what everybody intuitively understands: a well-engineered cleaning fluid will enhance the removal of contaminants from the optical end-face.
Since that time much has changed. Fiber optics technologies are no longer the exclusive, exotic technology of the monolithic phone company but an enabling capability of almost every company (and soon, every home). Mobile video on demand has created skyrocketing demand for greater bandwidth. Computing technology has plummeted in cost and expanded in capability. All of this means networks have become larger, commonplace and faster. Good news, all of it.
Except for one odd little quirk: fiber networks, as they have become ubiquitous also have become more fragile.
We don’t expect this from our electronics, do we? Today’s cell phone is far better than the model from a few years ago. Today’s laptop vastly outperforms the first Compaq “luggable” computer, and today’s flat-screen TV… well, don’t even try to compare a WIFI-enabled, 80-inch screen to the color TVs of the 1970s.
But today’s fiber, while more capable, is positively delicate. The first fiber link that Bell Labs built under the streets of Atlanta in 1976 operated at 44.7 mhz. The lasers generated a pulse of light that was enormously long by today’s standard: literally hundreds of meters in length. But as fast as it seemed at the time, in today’s world 44.7 mhz is not just a lethargic, it’s comatose. Modern networks work at gigahertz speeds which means (since the speed of light is constant) the pulse of light is just inches long. Such an ephemeral signal is easily “knocked off the rails” by the slightest contamination on the end-faces.
Everything has changed, except that technicians around the globe still are trying to clean their fiber with IPA. This is no longer a good idea.
First, reagent-grade IPA is not readily available to fiber optic technicians, and ordinary alcohol is completely unsuitable for cleaning fiber optics. For example, drug store IPA is not an optical-grade cleaner because it always is diluted with water to lower the cost; it is often 30% water. The mixture is packaged in a (relatively) dirty plastic container from which all sorts of plasticizers and contaminates may leach. The container may be re-used, and it certainly will become contaminated as it rides around in the back of an installer’s truck for months or even years.
Next, alcohol actually isn’t a very good cleaner. In terms of solvent technology, it’s pretty far down on the list of “old technologies.” It has a very low density so it cannot easily clean particulate. It has a high boiling point so it is relatively slow to dry. It is easily saturated, so it will no longer be effective. Modern cleaning chemistries usually try to avoid, or at least minimize, the presence of alcohols in the fluid because of these problems.
Thirdly, IPA is easily contaminated. Alcohol has a property of being “infinitely hygroscopic” which means it likes water; it wants to absorb water. This property means that IPA in loosely sealed bottles in the back of a truck will absorb moisture from the air along with any contamination that resides in the air. This is why IPA often leaves a “water-mark” residue on the connector end-face. These residues can “burn” into the surface of the glass and increase the signal loss of the connector permanently, requiring time-consuming re-termination.
Lastly, alcohol is flammable. It cannot be carried on to an airplane nor easily shipped without hazmat paperwork and fees. This means that technicians, installing and repairing fiber links in remote locations, often have to leave their cleaning fluid at home: not a good plan if you wish to have a happy, reliable, fast fiber network.
Becoming aware of the problems of alcohol, many folks discontinued the use of solvents and went with dry cleaning only. However, that has been proven to be less than desirable. As it turns out, wiping dry on a fiber end-face will generate a static charge (technically known as a “triboelectric charge”) on that end-face that is extremely difficult to dissipate. (These charges are like the ones you generated in school when you rubbed silk on a glass rod, fur on a hard rubber rod, or a rubber balloon on your hair.) This static charge turns the end-face into a microscopic magnet, attracting dust out of the air right on to the heart of the end-face.
Triboeclectric charging will occur when rubbing any nonconductive surface with any dry wipe, such as a “Cletop” or a fabric wipe. The build-up of this “static” charge on a connector end-face will attract unwanted airborne particulate and dust to the connector end-face. The condition will be exacerbated in dry conditions (low humidity) such as winter cold or desert heat. (See: Accumulation of Particles Near the Core During Repetitive Fiber Connector Matings and De-matings by Tatiana Berdinskikh, Jeno Chen Celestica International Inc, John M Culbert Megladon Manufacturing Group Ltd., David Fisher Tyco Electronics, Sun-Yuan Huang Intel Corp, Brian J. Roche Cisco Systems, Inc, Heather Tkalec Alcatel Corp, Douglas H. Wilson, Steven B. Ainley PVI Systems Inc. presented at NFOEC 2007). Therefore the use of static dissipative solvents during the wet/dry cleaning of connector end-faces is now the recommended practice.
With data rates over fiber only increasing, the need to clean properly has never been more important. A modern, water-free, high-purity fluid engineered for cleaning fiber optic connectors will both dissipate, and at least temporarily prevent, this build-up of triboelectric charges in the connector end-face. Therefore solvents should play an import role in cleaning.
During the wet/dry cleaning process, a section of the cleaning wipe is dampened with the cleaning fluid. The connector end-face is wiped, usually moving from the damp area towards the dry area of the cleaning material. (In the case of port cleaning sticks or automated devices, a cleaning stick or device is dampened with a solvent and used to clean the end-face.) When a fast-drying, static-dissipative fluid is used with a wipe or highly absorbent cleaning stick, no drying step is necessary. This saves time, money and cleaning supplies.
When a user (or corporate buyer) is selecting a fiber optic cleaning fluid, there are several factors that should be considered. The first consideration is whether the solvent readily removes a wide variety of soils and unwanted contaminates. This is easily tested in the field with sample product. Also, the user should make sure that the fluid is compatible with the wiping material or cleaning swabs. For example, one would not want to pair a solvent with a swab or wipe which was constructed of a material that the liquid would dissolve (perhaps a glue used in construction of the swab).
The second consideration is the safety of the solvent. Is the cleaning fluid flammable? Is the cleaning fluid safe for technicians to handle? Can it be shipped as a non-hazardour material? Will it freeze? Is it safe for the environment? The answers will be found on the product spec sheet and the MSDS sheet for the cleaning fluid. If the answers are not instantly available on the published documents, this usually is a sign of a vendor not fully disclosing the contents and properties of the material. Chose another vendor.
Another consideration is the speed of drying of the solvent: faster is better. Slower drying solvents require more time or more wiping to dry (which can delay progress, and also contribute to static charge build-up). But more importantly, slower drying solvents can “hang” in the split of the alignment sleeve of an adaptor or optical port of device. The trapped liquid, which cannot be seen with an inspection scope, then can then weep back onto the connector end-face spreading contamination. Very fast drying solvents will not remain in the liquid state long enough to become trapped within an alignment sleeve. (This has been demonstrated for IPA when compared to a faster-drying fluid). An water-based cleaner would certainly require very special attention to drying. (In the manufacture of precision optics, many aqueous cleaners have been replaced with fast-drying fluids to eliminate spotting and drying issues.)
Another consideration is the packaging of the fluid. The ideal packaging will prevent spillage, prevent re-contamination of the fluid during storage and normal use, and only dispense in quantities that are well-suited for a single cleaning. The fluid should be safe to use over a wide temperature range and should not freeze in field applications. Spilling is another worry; it can be costly and dangerous, particularly in the case of flammable liquids. Open containers (bottles) or pump-type dispensers easily can be contaminated from wipes, airborne contaminates or by refilling with unapproved fluids. Metered pumps are the ideal dispenser since the user cannot “over apply” a solvent (which can also be costly and dangerous). Excessive use of solvents is very easy with uncontrolled aerosol sprays.
Consider also materials compatibility. A well-engineered fluid will be compatible and safe to use with a wide range of materials including optics, plastics, metals, elastomers, electronic assemblies and adhesives. A proper cleaning fluid will dry without residue, and will not create unwanted corrosion, surface crazing, or otherwise damage /alter the connector end-face, its housing, or surrounding associated equipment.
The environmental impact of the fluid is important as well. The U.S. Government has four classifications of chemicals effecting air quality and the environment. The classifications are VOCs (Volatile Organic Compounds, which contribute to ground level ozone and smog), ODPs (Ozone Depleting Pollutants, which breakdown the protective ozone layer of the atmosphere), HAPs (Hazardous Air Pollutants, which consists of a list of chemicals whose use must be measured and monitored), and lastly GWP (Global Warming Potential, a measure of the potential damage to the environment over 100 years). In general, most fluids cannot be positive in all four categories. For example, if a material is not a VOC then it probably has a higher Global Warming material. Trade-offs must be made. The best recommendation is to select the safest solvent that will satisfactorily perform the cleaning task and select the best packaging to utilise as little fluid as possible.
Lastly, one must consider the cost, which must include the cost of the solvent, the safe storage and transport of the solvent (shipping), and the packaging of the solvent (the likely amount of solvent used per clean). Engineers should search for the “lowest cost per connector cleaned” to make bona-fide comparisons among competing products.
In conclusion, users will need new cleaning fluids in data centers, telco central offices, cable TV head-ends, and out in the field to clean today’s fiber optic connectors. There are many considerations that must be taken into account to provide the best product for the user. Price per can or bottle alone does not reflect the real cost. We all have responsibilities to provide for user with a fluid and a package that is safe, convenient, reliable and environmentally responsible.