OTDR stands for optical time domain reflectometer, and is an optoelectronic instrument that is used to characterize specific optical fibers. This tool injects optical pulses in series into fibers for testing as well as extracting light form that fiber that is reflected back from points in that specific fiber where the refraction changes. The strength of return pulses are then measured in time and then plotted under a function of the fiber length.
OTDR tools are used for helping to estimate the length of fiber’s attenuation such as splice and connector losses. This tool can also be used to help find faults or breaks and to measure the optical return loss. These tools are also used for their graphical display, as they can offer additional test automation, and requires special training and experience to use properly even though the information provided on screen is self explanatory.
OTDR tools are used to find the loss or length of a fiber from the point of manufacture to cabling and warehousing in a drum, then through installing and splicing. OTDR tests are stored for later use of fiber failures or warranty problems, as these failures can be very expensive. These tools are commonly used for finding faults in systems that are already installed. Reference in these cases helps to find where the problem lies. Using an OTDR for finding faults requires a professional operator who can determine the settings required for such a job, especially in cases over longer distances or splices and connectors that are closely situated with other PONs.
An OTDR can be available with different fiber types or wavelengths, so that common applications can be matched. Testing at longer wavelengths like 1550 mm or 1625 mm can be utilized to find attenuation issues rather than splice and connector issues. The optical dynamic range of OTDR tools are limited by the optical pulse width, input sensitivity as well as signal integration time and output powers. The optical pulse signal and integration time can be adjusted on these tools. Longer laser pulses improve the range and attenuation measurement resolutions, but take away from the distance resolutions. Short pulse lengths will help the distance resolution of optical events and can reduce the range of measurement or attenuation measurement.
The most commonly used OTDR tools available offer leading technology with power meter functions in one unit. These tools are optimized for PON point to point testing inside of FTTx architectures due to the fact that many different wavelength configurations and options are available.
Many of these tools are designed for PON troubleshooting with an optional port for testing at a regular 1625 mm incorporating a filter that gets rid of unwanted 1310, 1490 and 1550 mm signals that can affect the measurement. The in service tool troubleshooting features of optical fiber is not interfering with normal operations, and are not seen to interfere with CO’s laser transmitters. These use out of band wavelengths as is stated for recommendation in the ITU-T L.41, which is the Maintenance Wavelength on Fibers Carrying Signals.