What Is OTDR?
OTDR stands for an optical time-domain reflectometer. It is an instrument used to test an optical fiber. This equipment works by injecting a series of optical pulses into the fiber and extracts, from the same end, the light that is scattered (Rayleigh backscatter) or reflected back (Fresnel reflections) from points along the fiber. This technology uses the scattered or reflected light that is gathered to portray the optical fiber.
Optical Time-Domain Reflectometer (OTDR)
The Benefits of an OTDR:
This equipment can locate defects and faults, and can also determine the amount of signal loss at any point in a fiber optic run.
An OTDR machine only needs to have access to one end of a fiber to make their measurements.
This technology allows the machine to take thousands of measurements along a fiber. Using this it shows a snapshot of the cable run that is displayed on the screen as a line sloping down from left to right, showing distance on the horizontal line and signal level on the vertical line.
OTDR machines are widely used in all phases of a fiber system’s life from installation, maintenance, fault locating to restoration. If you are installing an outside plant network you will want an OTDR to check that the slices along the run and that the fiber itself is good. OTDR machines locate splices after they are made and confirm the performance of the joint.
An OTDR can also find any stress fractures in the cables caused by improper handlings, such as exceeding the bend radius, during installation. If you are doing any restoration because a cable has been cut, an OTDR will help find where it has been cut and assist to confirm the quality of the splice after restoration. On single-mode fibers where connector reflections are of a concern, an OTDR will pinpoint any issue very easily.
OTDR Symbol Meanings
An OTDR contains a laser diode source, a photodiode detector and a highly accurate timing circuit (or time base). The laser emits a pulse of light at a specific wavelength, this pulse of light travels along the fiber being tested, as the pulse moves down the fiber portions of the transmitted light are reflected/refracted or scattered back down the fiber to the photo detector in the OTDR. The intensity of this returning light and the time taken for it to arrive back at the detector tells us the loss value (insertion and reflection), type and location of an event in the fiber link.