Lightwave Communications LDX-3232 - Manual (Page 103)

FU N C T I O N S A N D FE A T U R E S
Modulating the Laser Current Source
04_06 LDX-3232 87
C H A P T E R
5
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 1 k
Ω. The transfer function for the low and high current ranges
of the LDX-3232 are 200 mA/V and 400 mA/V.
Set the LDX-3232 in Constant Current High Bandwidth
Mode by selecting I
HBW
in the MODE section of the front
panel. Do this by toggling the (MODE) SELECT push
button until the I
HBW
indicator is illuminated. Repeatedly
pressing the (MODE) SELECT switch cycles through the
current (I), optical power (P), or high bandwidth current
(I
HBW
) control modes.
Next, set the current source range by selecting the
2000 mA range indicated by the accompanying LED. You
will need to press the select push button twice to change
the range. It must be pressed twice quickly (within less than
one second) to switch between modes, and the current
source output must be off (MODE ON indicator unlit) in
order to change ranges.
The limit clamp function for DC output current applies to the modulated current as
well protecting your laser in any mode. To accomplish setting the current source
limit, use the (PARAMETER) SELECT push button LIM I. Press the
(PARAMETER) SET push button and rotate the adjust knob. Set the limit to
1750 mA. Once the (PARAMETER) SET push button is released, the new
parameter value is stored in non-volatile memory.
When the laser current limit is reached, the CURRENT LIMIT error indicator
flashes. The current limit setting is independent of the voltage drop of the device
connected to the laser output, and therefore, no dummy load is required for
precise adjustment of the current limit. Furthermore, since the current limit
circuitry is fully independent of the main current control, the current limit can be
adjusted safely, even while the current source output is active.
Now you are ready to modulate the laser injection current. To enable the Current
Source output, press the push button labeled (MODE) OUTPUT. The
accompanying LED labeled ON will illuminate indicating that the laser current
source's output is enabled. The instrument will drive the current source to the
value set by the corresponding MODE setpoint. Turn on the function generator
(modulation source) to inject the modulation signal.