EXFO T100S-HP Essential, Руководство пользователя, Страница: 47 / 70

Using the Auxiliary Inputs and Outputs
T100S-HP User Guide 47
The relationship between the voltage at the HF Mod input and the current added to
the diode is given by:
I
in
= V
in
/R
internal
where:
• I
in
is the added current
• V
in
is the voltage applied to the HF Mod input
• R
internal
is the50 Ω internal resistor of your T100S-HP
By modulating this extra current, the optical power output can be modulated within a
frequency range from 30 kHz to 200 MHz. The low-frequency cutoff is 30 kHz. The
modulation bandwidth is greater than 200 MHz, and this
HF Mod input can also be
used for mode-locked operation.
The best way to fulfill the above conditions is to measure the system bias current (I
b
)
through the voltage on the current monitor output, and to compute the total current
using the following formula:
Where:
• I
diode
is the total current through the diode
• I
bias
is the bias current
• V
in
is the voltage applied to the HF Mod input
• R
internal
is the 50 Ω T100S-HP internal resistor
Resulting HF-
Modulated Diode
Current You must monitor V
in
to ensure that the total current remains positive and lower than the
maximum admissible current, as shown in the following figure:
0 < I
diode
< I
max
Figure 11: Resulting HF-modulated diode current
Idiode Ibias
Vin
Rinternal
-------------------------
+ =
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
I
max
I
A
I
B
0
I
A

I
max
I
B

0