EXFO T100S-HP Essential, User Manual, Page: 45 / 70

Using the Auxiliary Inputs and Outputs
T100S-HP User Guide 45
Figure 9: Resulting LF-modulated diode current
In the APC mode, the output power is controlled in order to remain constant. In principle
this is not compatible with a modulation of the output power.
However, if the frequency of the modulation signal is well above the intrinsic frequency
(
≈
1 kHz) of the APC loop, the average power is monitored, and remains constant.
Modulation is possible in the APC mode at frequencies above 30 kHz. If a lower
frequency is used, interaction between modulation signal and APC circuit will cause
unpredictable modifications of the output power waveform.
I
bias
t
I
bias
t
V
in
t
I
diode
I
diode

I
bias
Diode modulated current
Current set on T100S-HP
without modulation
Input modulated
current