What is an OTDR?

An Optical Time Domain Reflectometer (OTDR) is used in fiber optics to measure the time and intensity of the light reflected on an optical fiber. More to the point, it is used as a troubleshooting device to find faults, splices, and bends in fiber optic cables, with an eye toward identifying light loss. Light loss is especially important in fiber optic cables because it can interfere with the transmission of data. An OTDR can detect such light loss and pinpoint trouble areas, making repairs easy. The more quickly trouble areas are identified and addressed, the less your fiber optic network will suffer from data transfer problems.

The physical description of an OTDR most closely resembles a sort of handheld price scanner with cables attached. The user connects the cables to an optical fiber, in the same way that two drivers will connect vehicle batteries with jumper cables, and then reset the OTDR settings for whatever parameters are being used in the specific test. A typical OTDR test can take anywhere from ten seconds to three minutes.

An OTDR takes advantage of the scattering of light in the optic fiber to make its measurements. The OTDR emits a high-power pulse that hits the fiber and bounces back. What comes back is measured, factoring in time and distance, and the result is "trouble spots," which radiate and can be targeted for repair. In general, the data take the form of a wave, with trouble spots clearly visible as aberrations in the wave.

Some OTDR systems are equipped with PC-linking capabilities, so that the data recorded during testing can be downloaded to a computer for analysis and storage. Naturally, specific software applications are available for such analysis.

The OTDR is not perfect, of course. Critics charge that it can produce inaccurate results if two trouble spots are very close together or if the pulse has a long travel length. Experts also urge training in order to interpret the data correctly. Another factor is the relatively high price for a device that might be used only sparingly. Proponents, however, counter that being able to pinpoint and address light loss points is well worth the price, both for the OTDR device and for the training needed to operate and properly understand the data that that OTDR records.