Optical time domain reflectometer

An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber. An OTDR is the optical equivalent of an electronic time domain reflectometer. It injects a series of optical pulses into the fiber under test and extracts, from the same end of the fiber, light that is scattered (Rayleigh backscatter) or reflected back from points along the fiber. The scattered or reflected light that is gathered back is used to characterize the optical fiber. This is equivalent to the way that an electronic time-domain meter measures reflections caused by changes in the impedance of the cable under test. The strength of the return pulses is measured and integrated as a function of time, and plotted as a function of fiber length.

The reliability and quality of an OTDR is based on its accuracy, measurement range, ability to resolve and measure closely spaced events, measurement speed, and ability to perform satisfactorily under various environmental extremes and after various types of physical abuse. The instrument is also judged on the basis of its cost, features provided, size, weight, and ease of use.

Some of the terms often used in specifying the quality of an OTDR are as follows:

Industry requirements for the reliability and quality of OTDRs are specified in the Generic Requirements for Optical Time Domain Reflectometer (OTDR) Type Equipment.

The common types of OTDR-like test equipment are:

In the late 1990s, OTDR industry representatives and the OTDR user community developed a unique data format to store and analyze OTDR fiber data. This data was based on the specifications in GR-196, Generic Requirements for Optical Time Domain Reflectometer (OTDR) Type Equipment. The goal was for the data format to be truly universal, in that it was intended to be implemented by all OTDR manufacturers. OTDR suppliers developed the software to implement the data format. As they proceeded, they identified inconsistencies in the format, along with areas of misunderstanding among users.

From 1997 to 2000, a group of OTDR supplier software specialists attempted to resolve problems and inconsistencies in what was then called the “Bellcore” OTDR Data Format. This group, called the OTDR Data Format Users Group (ODFUG), made progress. Since then, many OTDR developers continued to work with other developers to solve individual interaction problems and enable cross use between manufacturers.

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