Fiber Optics Make Repair Techs Lonely
How often have you discussed new and better technology applications with your customers only to have them cringe at the thought of new performance problems? One technology area that you can promise just the opposite is fiber-optic cabling. In fact, I would go as far as to tell them they might even find this technology boring.
Do you remember the Maytag commercial about that famous washing machine repairman who hardly ever had a repair call and sat around the service office waiting for the phone to ring? Well this could very well be the life of someone who has to service a fiber optic-based system. Typical security and CCTV system troubles caused by lightning, induced noise and ground loops are now a thing of the past.
However, to get a fiber optics-connected system up and running one has to have a good understanding of the types of fiber-optic cabling and connectivity. Once this is mastered, you too can have a virtually trouble-free system. This should be a major selling point with your customers and prospects.
Get Your Hands on Training, Tools
First, we should all have a good basic understanding of fiber-optic fundamentals.
There are a couple of sources I can recommend. One is the Corning Cable Systems Web site (www.corningcablesystems.com). Corning is the primary manufacturer of the glass fiber used in fiber-optic systems. Make sure to check out the industry and organization links at this company’s site for more fiber-optic tech info.
Another good read is the Fiber Optic Design Guide from International Fiber Systems Inc. (www.ifs.com). Make sure to contact the company for a copy.
Fiber installation and test equipment is now more user-friendly and cost-effective than ever. In the past, it took a small fortune for a contractor to get into installing, testing and servicing fiber optics. While any initial equipment outlay can still cost around $1,000, the investment will be returned in the integrator’s new high-tech specialty and services to customers.
With fiber connection inspection tools now running less than $200 and electronic fiber inspection camera scopes less than $400, basic reliable “starter” equipment is within the reach of even the smallest contractor.
Additionally, it is very important for the serious fiber-optics installer to get some good training. This should include hands-on, classroom training in order to get the feel for how to make a professional fiber connection. I would not only check fiber equipment manufacturers, but organizations such as the Building Industry Consulting Service Int’l (BICSI) and National Burglar and Fire Alarm Association (NBFAA) for regional training sessions. Some of the links above in this article can offer good sources for training as well.
Figuring Path Loss, Power Budget
If you are going to be responsible for planning and/or proposing a system that will communicate over fiber, you will need to do some basic calculations such as optical path loss and power budget calculations.
Since you are dealing with light transmission, optical path loss can be from optical connectors, splices/connectors, patch panels and fiber attenuation at a particular wavelength (see diagram on page 24 of May issue). Loss is measured in decibels (dBs) and is additive with respect to any of the above components.
Fiber cable loss is measured in dB per kilometer (dB/Km) at the wavelength of the transmitter. For example, a fiber cable path that has a 3dB cable attenuation loss, a 0.6dB splice attenuation loss and a 3dB patch panel attenuation loss would have an optical path loss of 6.6dB.
Now that you have calculated your optical power loss, you should check your optical power budget. Why? This will tell you if you have picked fiber transmission equipment that has enough power and fiber receivers that have enough sensitivity to comfortably overcome your already calculated optical path loss. This, of course, assumes you have made good optical connections and picked the right fiber cable.
Again, since we are dealing with dB calculations, we will subtract the receiver sensitivity from the transmitter output power. So if we had a transmitter with -14dBm and a receiver with -28dBm, our optical power budget would be 14dB.
I think by now you are catching on. Does our optical budget exceed our optical losses and by how much? This positive amount is our safety margin and will vary depending on equipment cost and performance tradeoffs. In our example we have 7.4dB safety margin.
Fiber design professionals recommend a minimal safety margin of 50 percent or 3dB attenuation for unexpected losses. Also, you may want to add an additional 3dB to cover any future splicing work.
Fine Tuning Your Fiber Technique
Now that you can do these calculations, you can mix and match fiber cable, connectors and other equipment in order to find the most economical system for the particular application. Many security applications will work well with more economical multimode fiber cable, while an extremely long-distance application may need more expensive single-mode optical fiber to compensate for optical path losses.
Fiber-optic cable is physically handled differently than copper cable. We must remember that even though it appears very thin and flexible, it is a fine glass wave-guide for light — even the slightest alteration of this internal core can cause severe attenuation.
Care should be given when pulling fiber. A swivel-pulling eye should be used to minimize twisting of the cable. It is highly recommended to use an inner-duct pathway, even within EMT conduit for fiber-cable protection. Many come specially coated for fiber or with preinstalled pull strings.
To minimize cable twisting, roll the fiber cable off the side of the spool and do not pull it off the top of the spool. If you need to temporarily hold pulled fiber cable at a junction box, lay the cable out in a figure-eight pattern rather than a large coil. Fiber cable comes with a strong Kevlar fiber; make sure to use that fiber for pulling. Since fiber cable is so light, one popular method of getting it through inner-duct and conduit is by using compressed air to blow the fiber cable. One special blowing method is done through what is called “micro-duct” with systems such as Blolite™.
These types of systems can have miniature multi-duct configurations. Each duct can have up to 12 fibers. A fiber can be blown through in minutes in runs up to 3,000 feet, and with up to 300 right angle turns. This type of planned fiber network installation can open ducts for future expansion. Fiber can be blown back out and removed for higher bandwidth upgrades.
Precautions for Working With Fiber
Safety is a big concern when working with fiber-optic systems. Make sure to use either a nondirect camera-type inspection scope or microscopes with laser safety optical filters when examining the quality of a splice. Work on a dark surface when making fiber splices so you can see all cut fiber pieces, as a broken glass splinter can get easily lost under the skin. Use some double-stick tape to help collect and inventory loose fiber scraps when splicing.
Here are some last-minute tips on making connections: Make sure your work area is clean and avoid working near vents that could blow dust. Use lint-free pads and a nonresidue cleaner such as isopropyl alcohol to clean connectors. Keep dust caps on any connection device. Be careful about getting the ferrules on the testing connector cables dirty. Use only metal or ceramic alignment sleeve bulkheads for testing.
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