Exfo FTB-7000 OTDR for FTB-200 v2 Uživatelský manuál stáhnout pdf (Strana 208)

Analyzing Traces with the Bidirectional Analysis Application

194 FTB-7000 Series

³ Bidirectional analysis is the recommended method for splice loss

measurements on singlemode fibers by the Telecommunications

Industry Association (test procedure EIA/TIA FOTP-61 Measurement of

Fiber or Cable Attenuation Using an OTDR).

This method removes the so-called “gainers” (increase in the optical

power) and exaggerated losses and provides accurate measurements.

This analysis is particularly useful to test the quality of a link, especially

if it comprises several sections with different types of fibers or fibers

from different manufacturers.

Gainers and exaggerated losses result from the joining of two fibers of

different mode-field diameters (MFD). The mode-field diameter of a

fiber corresponds to the size of the area where light is dispersed across

its core and cladding.

Mismatch of MFDs will contribute to differences in back-reflected

signal that are not related to the loss at the splice point, that is to the

true loss seen in transmission. In this case, a unidirectional OTDR trace

will show an apparent increase (gainer) or decrease (exaggerated

loss) in signal, depending on the direction of measurement.

Bidirectional averaging of OTDR splice loss measurements provides

the most accurate splice loss results.

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Exfo FTB-7000 OTDR for FTB-200 v2 Uživatelský manuál Strana 208