ILX Lightwave LDC-3908, User Manual

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FU N C T I O N S A N D FE A T U R E S
Modulating the Controller Laser Current Sources
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LDC-3908
C H A P T E R
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Modulating the Controller Laser Current Sources
The LDC-3908 Laser Diode Controller allows a modulated signal to be superimposed on the Laser
current of any or all current source modules. The Modulation connector (BNC) on the back panel is
the input for the modulated signal. This input is terminated into 50
Ω .
Each module uses an instrumentation amplifier to buffer the modulation signal. This signal may be
applied to more than one module (channel) at a time. The transfer function (mA/V) varies by model
and laser drive current output range. Typically it is mA (full scale) / 10 V.
Laser protection is assured, even while modulating, via the limit current parameter set on each
individual module. Refer to the appropriate module manual for details on limit current settings and
laser diode protection.
The allowable bandwidth of the modulated signal, defined as the 3 dB roll-off point, is dependent
on the current source module used, the Laser current range, and the Laser mode (constant current,
low/high bandwidth). See the section, Laser Current Source Specifications, in Chapter 1 of the
appropriate module's instruction manual for external analog modulation bandwidth specifications.
Modulation Setup Example
For example, assume you are using an LED that must be operated in constant current of 50 mA
with a modulated injection current from 3 to 30 kHz. The experiment requires an LDC-3916372 laser
controller module to be configured for high bandwidth mode with a limit of 175 mA.
Set the LDC-3916372 module in Constant Current High Bandwidth Mode by selecting IHBW in the
LAS
menu on the front panel. Set the current to 50 mA and set the current limit for the LDC-3916372
as desired. Enable modulation by selecting On for the Modulation selection in the LAS p.3 (laser
page 3) menu. Now you are ready to modulate the laser current.
From the LAS menu, press the Off key to toggle the laser current output on. The soft key indicator
will change to On. To turn the output off, press the On key to toggle it Off again.
Note: If the modulation signal attempts to drive the output above the LAS ILIM (laser
current limit) setting, the output will be clipped at the ILIM value.
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