Modulating The Laser Current Source - ILX Lightwave LDX-3200 Series User Manual

MODULATING THE LASER CURRENT SOURCE

The LDX-3200 Series Current Source allows a modulated signal to be superimposed on the source output current. For
example, assume you are using an LED for your experiment where you need to operate the LED in constant current at
P = 1 mW, with a modulated signal from 3 to 30 kHz. The experiment requires the LDX-3220's laser Current Source
OP
to be configured for the 200 mA range, high bandwidth mode with a limit of 175 mA. The allowable bandwidth of the
modulated analog signal, defined as the 3 dB roll off point, is dependent on the LDX-3200 Series family member, the
output current range, and the mode (constant current low/high bandwidth). See the section, LASER CURRENT
SOURCE SPECIFICATIONS, in Chapter 1 for external analog modulation bandwidth specifications.
Setting up the Current Source for a modulated laser injection current is easy. The (MOD)
EXTERNAL connector (BNC), on the front panel, is the input for the modulated signal. Connect
a modulating voltage signal from a standard function generator, for example, to this connector.
The modulation port input impedance is 10 kΩ. The transfer function (mA/V) shown is for the
LDX-3220. This transfer function varies by model and laser drive current output range. The
transfer function for the low and high current ranges of the LDX-3210 are 5 mA/V and 10 mA/V.
FUNCTIONS AND FEATURES
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TRIGGER OUTPUT BNC
FIGURE 5.1 LDX-3200 Series Rear Panel
Set the LDX-3200 in Constant Current High Bandwidth Mode by selecting I
MODE section of the front panel. Do this by toggling the (MODE) SELECT push button
until the I indicator is illuminated. Repeatedly pressing the (MODE) SELECT switch
HBW
cycles through the current (I), light power (P), or high bandwidth current (I
modes.
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in the
HBW
) control
HBW
CHPT 5