EXFO IQS-1600 High-Speed Power Meter for IQS-500/600 - Manual (Page 110)

Typical Applications
102 IQS-1600
Characterizing an Optical Switch
7. Set the switch to the first position and take a reference measurement
on the channel receiving the signal.
8. Set the switch to the second position and take a reference
measurement on the second channel, now receiving the signal.
9. Change the switch position from one channel to the other. For each
channel, take note of the relative power measurement when the
channel is active.
10. Repeat step 9 as many times as required.
11. For each channel, the total deviation will be the highest positive
deviation minus the highest negative deviation relative to the original
reference (taken at step 4). The repeatability of the switch insertion
loss may be expressed as ± (total deviation in dB)/2.