EXFO IQS-12002B Calibration System - Manual (Page 77)

Calibration Methods
Calibration System 73
FTB-7000D and FTB-7000B-B OTDR Modules
Distance Calibration Method
Distance is calibrated with the use of a reference fiber that is traceable to a
national metrology institute (e.g. METAS, NPL, NIST, NRC).
The following diagram shows the setup used by EXFO for distance
calibration.
For multimode OTDRs, calibration is performed on the same fiber for both
50/125 and 62/125 OTDRs (the difference in dispersion in the fiber has a
negligible impact). A 3-meter test Jumper is connected at the far end of the
reference fiber in order to have a similar reflection at both ends.
For singlemode calibration, since the OTDR could be equipped with an
output APC connector, the setup requires a short fiber spool (about
50 m ±1 m) to be installed before the reference fiber. This is done so that
you can set markers at each end of a known reflection of similar level (as
that given by FC UPC to FC UPC connectors: about 55 dB). This also has the
great advantage of allowing the use of an uncalibrated test jumper to
connect an OTDR, equipped with an APC connector at the output, to the
short fiber spool of 50 m.
Fiber spool (50 m) Singlemode fiber (2300 m)
reference standard
FC UPC/FC UPC
OTDR
FC UPC/FC UPC FC APC
Fiber (3 m)
Multimode fiber (100 m)
reference standard
OTDR
FC UPC/FC UPC FC APC