How to Repair a Cut Underground Fiber-Optic Cable

Sine Wave

According to the Electronic Technicians Association, one of the chief causes of failure in fiber-optic cable is "backhoe fade," a technical term meaning that someone using a backhoe has cut your cable. If this happened on property that you own, finding the break is easy: Look for the backhoe. Other causes, though, might not have easy solutions. Moles love to chew on fiber-optic cables, and unfortunately, they're a little harder to see than a piece of heavy equipment. This means that finding the break becomes an expensive process because of the equipment involved.

Things You'll Need

• Optical time-domain reflectometer Quick-connect fiber-optic connectors Cable gel remover Cable rip cord Fiber-coating stripper tool High-precision fiber cleaver Buffer tube stripper Fusion splice protector sleeve Fiber-optic fusion splicer Heat shrink oven Fiber-optic cable splice enclosure Optical fusion splicer Shovel Screwdriver (standard flat blade, to close splice enclosure) Work gloves Safety glasses

Instructions

1. Find the break in your cable. Fiber-optic technicians use a device called an optical time-domain reflectometer( OTDR). When connected to fiber-optic cable, the OTDR works much like radar, sending a light pulse down the cable, which is reflected back to the device when a break is encountered. This tells the technician how far down the line of cable the break is located.

2. Dig up the cable at the location the OTDR has pinpointed as being the site of the break in the fiber-optic cable.

3. Prepare the fiber by stripping about 9 feet of the cable with the cable rip cord, and gently peel back the jacket to expose the fiber-optic tubes inside and remove the excess jacket. Clean the cable gel with cable gel remover, cutting away any yarn or sheath, and separate the fiber tubes. Try not to damage the strength member, as it's needed to hold the cable in the splice enclosure.

4. Use the fiber-coating stripper tool to expose 2 inches of fiber cladding, and clean all fibers in the tube with cable gel remover. Using the high-precision fiber cleaver, trim any damaged ends of the fibers. If you plan to do a fusion splice, put a fusion splice protector sleeve onto the fiber, then clean the stripped fiber with lint-free wipes soaked in household alcohol. If you plan to make a mechanical connection, put the quick-connect fiber-optic connectors on the fiber, and wipe the stripped fiber using lint-free wipes and alcohol. Don't let the fiber touch anything. Repeat this process, inserting the fibers into the corresponding fusion splice protector sleeve or the quick-connect fiber-optic connectors. If you are using quick-connect connectors, this completes the splicing process.

5. Put the fibers to be spliced in the fusion splicer if you're making a fusion splice, and fire the fusion splicer according to its manual. Then, move the fusion connector (with its associated fibers) into the heat shrink oven, and press the button to heat shrink the fusion connector in place on the fused fibers. The fusion splice is somewhat superior to the mechanical splice, because its signal (insertion) loss is less than 0.1 decibels (dB); the mechanical connection has an insertion loss of less than 0.5 dB. Check the fiber-optic connection with the OTDR. Put the splices into the splice enclosure, close the enclosure, and rebury the cable.

Tips & Warnings

• The mechanical connectors--the quick-connect fiber-optic connectors--are simpler and safer. The loss of quality as the result of using mechanical connectors is negligible.

• The optical fusion splicer generates a minor electrical explosion to fuse the ends of the fibers together; the heat shrink generates sufficient heat to burn a hand. While handling fiber-optic cable, do not allow the cable to exceed its bending radius.

Resources

• Casimer DeCusatis; Handbook of Fiber Optic Data Communication: A Practical Guide to Optical Networking, Academic Press, 2008