Proper fiber optic cleaning yields impressive results
by Rick Racinskas
Editor’s Note: This article is the second half of a two-part series. The first part appeared in April 2007 on page 15. The opinions expressed in this article regarding the attributes of specific products represent those of the author and do not represent an endorsement by Lightwave.
Being “connected” has changed our world in ways that our parents never could have imagined. It was stated recently that in three years, 20 homes alone will equal the bandwidth of the Internet circa 1995. One thing is for sure: We will be pumping more bits into neverending demand for data.
As we move into gigabit-plus rates, I feel compelled to wave a flag regarding fiber cleaning and inspection. I know it is about as exciting and technical as mud, but it is the single greatest cause of network failures, increased field returns, and even homes being rewired with heavier coax. The costs are unknown and maybe hidden, but I would estimate them to be hundreds of millions of dollars per year. In talking with Westover Scientific, I was amazed at their numbers: Some of the major telco/data vendors have 40% to 90% field return rates from dirty fiber. What is more amazing is how nobody seems outraged.
With singlemode fiber less than one-thousandth of an inch across, almost any type of particle will cause problems unless you thoroughly clean both ends before mating. We are all concerned about excess insertion loss caused by dirt or misalignment reducing our optical margins. A more interesting issue is that a small particle may add a marginal amount of loss but cause large increases in backreflection, which can wreak havoc with RF overlay systems or single-wavelength data links. Even worse, faster data pulses are more sensitive to path contamination. Upgrading your transceiver speeds can downgrade your network reliability. If you want your products or services to excel, become a fiber nut when it comes to training, cleaning, inspection, and enforcement. You’ll get a great return on a small investment. A good place to start is the free “Inspect before You Connect” training video from Westover Scientific (available at http://westoverfiber.com/Support/downloads.php).
There are many methods for cleaning and a variety of products are available. There is not one universal solution but great ones for different scenarios.
Cleaners for ferrules or pins: If you’re using alcohol (IPA),make sure you get optical grade (99%) and keep it capped because it will absorb moisture. If left moist, it makes a mess (see Photo 1). Avoid using for sockets unless very lightly applied. Excess solvent can be bad for lenses, etc. It must be “dry” cleaned immediately. It has MSDS, storage, handling, fire, and disposal issues.
Alternatively, specialized fiber-optic liquid sprays generally work well. Be aware of possible fire hazards and do “dry” clean as well. Avoid these sprays for sockets unless very lightly applied. They have MSDS, possible fire (some are very hazardous), and, of course, disposal issues (see Photo 2). Don’t ever use other liquids or solvents such as Windex or acetone. You need a mild, fast-drying cleaner that leaves no residue.
KimWipes and specialty cloths must be lint free. If you keep them clean, they work well with very low cost. They require more expertise and optical inspection for consistency. They’re great for a general “dry” clean.
Cletop/Optipop reel-style cleanersoverall are great products for general-purpose use with ease of use, consistent cleans, and a portable design. But don’t rewind the tapes.
Cleaners for pins and sockets: The HUXCleaner from The Fibers and the Seikoh Giken Ferrule Mate are great pen-type products for sockets and pins. Both do a nice job.
Automated cleaners, such as the products from Westover Scientific and Lightel, are great for low-cost production line cleaning once you get over the high capital cost. They are especially useful on socket contacts and transceivers.
Many companies make sticks or swabs and claim theirs are the best. It is very difficult to absorb all the contaminants, leaving the optical contact area pristine. So your results will vary. Just use fiber-grade (no cotton swabs, please) and toss after use.
Canned air is a favorite in lots of procedures because it is cheap and available. I don’t ever recommend it. The residue in some sprays is nasty and will cause more problems than it solves. Most contaminants require direct contact for removal. No-residue optical-grade spray is very expensive. Never allow “shop” air to be used, even if well filtered. It is near impossible to make the air clean to the micron level.
I don’t recommend most other products, either. If you do find something, do a thorough evaluation.
A proper cleaning method is dependent on your environment. Manufacturing, lab, and field/service applications should have differing methods.
In a manufacturing environment, the goals are speed, low cost, and ease of use. If it is not easy, it won’t get done or done well. Most contamination is simple dust and easy to deal with. Connecting cables seeing constant matings should be simply wiped with a Cletop (preferably white film) or a cloth wipe. Transceivers should get an automated or stick clean due to complexity. Product fiber test systems I design always include automated fiber inspection with daily calibrations.
For lab applications,I would recommend a Cletop for pins (ferrules) and a HUX or Ferrule Mate cleaner for sockets, preferably on a chain. Otherwise, they seem to walk away. Make refills easy to find or cleaning won’t get done. A video scope is a critical accessory to have nearby.
Field/service applications arethe most difficult of all. You may need a liquid to remove the oils, grease, and glue from labels. Then follow up with a good dry clean. In a service situation, you may want to do a fiber inspection and document contamination before doing any other tests, upgrades, or repairs. Several cleanings may be required. Make sure your procedure (you have one, don’t you?) covers how many loops you allow.
The importance of inspection is critical. For example, your cleaning process may have left residues or even added them. For inspection, I prefer the Fiberchek2 system from Westover Scientific. There is nothing like a quick objective pass/fail test. No need to refer to a 30-µm blob in Zone B in a procedure.
A microscope/video system is better than nothing, but you cannot calibrate, correlate, or store readings. The quality of the monitor and its settings make a huge difference. I recommend a 400X magnification for singlemode and 200X for multimode fiber. Handheld scopes are my least favorite and may be dangerous in some applications where EDFAs are involved. Remember the famous “Caution! Do not look into laser with remaining eye.”
It is important for your customers, installers, service folks, and anyone who uses your fiber-optic products or services to know how critical fiber cleanliness is. We have electrostatic discharge stickers on products to maintain awareness of that potential problem. I am of the belief that fiber cleaning is a more critical issue. Should we have a “Clean Me” sticker on optical boards, patch cords, panels, and test equipment? Why not? While I hope you have fiber handling/cleaning procedures, you need a group or individual in your company to maintain vigilance across the board.
It is most difficult to write an all-encompassing article where a book may be more appropriate. There seems to be precious little quality information on this issue. In general, if you want to avoid strange field issues, long weekends, and even longer customer conference calls, a strict program of fiber cleaning and inspection will make your life easier and your bottom line a little fatter. As the data rates climb skyward and the costs per hour go downward, you and your company will do well to take heed and keep your fiber connections clean.
Rick Racinskas is a senior engineer at Tellabs (www.tellabs.com), where he supports global manufacturing for the company’s access products. He has more than 20 years of experience in fiber-optic design, test, and manufacturing. Racinskas holds five patents and a bachelor’s degree in engineering technology from the University of South Florida. He recently taught fiber cleaning and inspection at OFC/NFOEC 2007 short form classes in conjunction with Dennis Horwitz. He can be contacted at firstname.lastname@example.org.