EXFO T100S-HP Essential, User Manual, Page: 44 / 70

Using the Auxiliary Inputs and Outputs
44 T100S-HP User Guide
• Make sure to use a 50 Ω BNC cord to connect the T100S-HP and the waveform
generator.
Figure 8: Low frequency modulation setup
2. Set the operating current I
bias
of the T100S-HP in constant-current mode.
The relationship between the diode output current I
diode
and the input voltage V
in
is
then given by:
Formula:
Where:
• V
in
is the input voltage applied to the LF Mod. BNC input connector ( V
in
must
always be positive and less than 5 V)
• I
diode
is the total diode current
• I
bias
is the polarization current of your T100S-HP
• R is the 50 Ω resistor of the LF modulation circuit
With a maximum allowed voltage input of 5 volts, the maximum input current you
can add to the T100S-HP laser diode is 100 mA.
Resulting LF-
Modulated Diode
Current The laser diode of your T100S-HP is characterized by its saturation current ( I
max
) and the
cutoff current ( I
cutoff
).
To perform a diode intensity modulation under optimum conditions, you must ensure at
all times that the resulting modulated diode current obeys the following condition:
I
cutoff
≤ I
diode
≤ I
max
The following figure shows a behavioral representation the resulting modulated diode
current.
T100S-HP Laser Diode Source
LF Modulation
Circuit
Waveform Generator
I
bias
Polarization Current
I
in
I
diode
V
in
BNC Cord
50
Ω
LF Mod.
BNC Connector
50
Ω
Idiode Ibias 2
Vin
R
--------

– =