EXFO IQS-12002B Calibration System - Manual (Page 75)

Calibration Methods
Calibration System 71
FTB-7000D and FTB-7000B-B OTDR Modules
The fiber section chosen for the loss measurement must be as far as
possible from the VOA to reduce errors due to recovery on the OTDR.
Usually, the fiber section is chosen to roughly emulate a 0.5-dB loss.
The initial measurement, performed at the minimum attenuation of the
VOA, is considered as the reference loss (A
ref
). Following measurements
are done at higher attenuation. The OTDR loss measurements (A
otdr
) must
meet the linearity criteria where nonlinearity (NL) is calculated this way:
The linearity specification must be met for a given attenuation range. This
range depends on the OTDR type, the pulse, and the wavelength. The
attenuation range is limited by noise on the trace or recovery after the VOA.
Note: There is no uncertainty value associated with this measurement.
1 max − ± =
ref
otdr
A
A
NL