Overview of Fiber Optic Testing
There are mandatory tests for every stage of the design, manufacture, and installation of the fiber optic components, link, cable plant, and network.
Most fiber optic test procedures have been thoroughly tested and codified as industry standards. These standards are part of EIA/TIA RS455 and are being adapted into IEC standards.
Most of these standards refer to tests of individual components under a variety of environmental conditions; therefore, only a few related to testing the performance of the installed cable plant.
With data communication networks, we are primarily concerned with three fiber optic test procedures: FOTP-95 for measurements of optical power, FOTP-171 for testing patch cables and OFSTP-14 for testing the loss of the installed cable plant.
Optical Fiber Testing
A great many tests must be performed on optical fibers. A fiber manufacturer must test a fiber to determine the characteristics by which the fiber will be specified. As a quality control measure during manufacture of fibers, the manufacturer must constantly test the fibers to ensure that they meet the specifications. Among the tests are the following: core diameter, cladding diameter, numerical aperture (NA), attenuation, refractive index profile and tensile strength.
Other tests performed on fibers or on fiber optic cables concern their mechanical and environment characteristics. Mechanical tests such as impact resistance, tensile loading, and crush resistance test the cable's ability to withstand physical and mechanical stresses. Environmental tests evaluate the changes in attenuation under extremes of temperature, repeated changes of temperature, and humidity.
Fiber Optic Cable Plant Testing
There are some testing concerns in a premises-cabling application based on the recommendations found in TIA/EIA-568A for generic cabling systems and TSB-67 on testing.
An important concept in testing is distinguishing between the link and the channel. The channel is the end-to-end system, including any patch cables at the equipment or work area. The link is the "behind-the-walls" cabling from the equipment-side patch panel to the work-area-side outlet.
Testing can be done on either a link level or a channel level. Installers of a building cabling system are usually concerned with the link. The link forms the basic infrastructure for the building cabling.
Fiber Optic Component Testing
Fiber optic data links are composed of three components: a transmitter, a receiver and the interconnection cable plant. These components must be compatible with the parameters of the intended application.
The loss budget must be adequate for the expected loss in the cable plant and the dynamic characteristics must meet the bandwidth requirements set by the network data transmission rate.
The loss budget is set by the output power of the transmitter and the sensitivity of the receiver. On a static basis, this is determined by the difference in optical power levels, but in reality the issue is a dynamic one, determined by the performance of the components at the data transmission rate of interest.
Continuity Testing
Simple continuity testing can be achieved by a flashlight: Does the light come through the fiber? Fancy flashlights - called visual continuity testers - are available specifically for fiber optic testing. A read light is easiest to see.
