What Are the Best Tips for Testing Fiber-Optic Cable?

Jo Dunaway

The best tips for testing fiber-optic cable include knowing the testing techniques and principles. Testing requires some specialized equipment and thorough knowledge of its operation. A good knowledge of networks, their construction, maintenance and possible sites of problems are equally necessary. All equipment should be tested prior to testing fiber-optic cable, and safety goggles are recommended. In most cases, successful testing of an installation and delivery of the results to a customer is the minimum necessary to consider the networking job completed. The motto “be prepared” is an essential guide when testing fiber-optic cable, as it’s considered unprofessional to need to call the manufacturer when on a job.

Special equipment must be used to test fiber-optic cables.
Special equipment must be used to test fiber-optic cables.

Before starting, gather the tools and perform the tests of reference jumper cables in both directions to ensure all of them are in good working order. If the power meter can generate reports of data, program it ahead of time for the specific reports necessary for the job. Gather cable layouts for all types of fiber-optic cable that will be tested and prepare a spreadsheet of all cables and connectors to be used on the job, before you go out into field testing operations. The very first consideration is to test all connectors with a power meter before looking into them, as some telecommunications and cable television networks have very high power.

Specialized equipment must be used to test fiber-optic cable.
Specialized equipment must be used to test fiber-optic cable.

Check for continuity to be certain the path of fibers from end to end through any connectors is sound and no fibers broken. Use a fiber-optic tracer tool with a light emitting diode (LED) source. Attach it to a cable and look down the length of the core to see if there are any breaks in the light’s path. If a break in the light path is found, trace it back to the prior connector to see if there is an actual break, which may necessitate section replacement, or if the fiber has become kinked or bent. Higher power tracers use lasers to find faults in connectors; additionally, a fiber-optic microscope should be used to inspect connector terminations. Medium magnification is best for viewing connectors at several angles to see if they are smooth and scratch-free or if there are any chips or any fiber protruding from the ferrule.

Optical power loss is the “relative” difference between power that is coupled in a fiber-optic cable component and the power being transmitted through it. This difference can be measured in connectors, splices and cables. After an installation, use a power meter or optical time-domain reflectometer (OTDR) to check levels of power loss of both the transmitter and the receiver, of each connector, splice, and of the entire system. Manufacturers' manuals will give the optimum measurements conversion factors and a list of maximum allowable losses. When testing a splice, make sure the splice was made with a fusion splicer at the bare minimum and redo the splice entirely, if not.

If there are high losses found in a cable, reverse it and test in the opposite direction; by this method it is possible to detect a bad connector in a network. The best tips for a testing fiber-optic cable stress the necessity of having good documentation on the network as a whole. It is essential to know where all the cables are going, how they were originally tested for loss and each cable’s length to have a basis for comparison testing. Isolate if the problem is with the cable or equipment using the cable by use of a power meter to test source output and receiver input and use a laser tracer to check for continuity in all fiber-optic cable. If it is a cable problem, the OTDR is the tool to use to locate the fault and guide through restoration. Ethernet fibers require careful cleaning and inspections to work properly or they may cause cross contamination to adjacent connectors; improper cleansers can destroy an Ethernet connector, so use the fiber optics microscope to check the connector end first.

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