Using The Laser Compliance Voltage Adjustment - ILX Lightwave LDX-3200 Series User Manual

USING THE LASER COMPLIANCE VOLTAGE ADJUSTMENT

For applications where you need to have critical protection of the laser we recommend the following. Using a one
ohm resistor or other non-critical load, set the LASER voltage limit as described in Chapter 2.
Then with the LASER output on, slowly increase the LASER current and watch the LASER voltage measurement.
Press the (DISPLAY) SELECT push button to see the voltage. At about 0.25 volts below the LASER voltage limit
value, the VOLTAGE LIMIT warning indicator will become lit on the display. Continue to adjust the current up until
the voltage limit is reached and the output is shut off. Record the voltage at which the LASER output shuts off. It
should be within the specification of the LASER voltage limit accuracy. However, there is typically some offset error.
For example, if the LASER voltage limit is set to 5.0 volts, the actual voltage where it shuts off may be 4.9 volts. This
error term of 0.1 volts should be considered when setting the LASER compliance voltage limit.
The closer the LASER voltage limit shut off point is to the operating voltage of your laser, the faster the circuit will
work in the event of an open circuit. Some experimentation may be necessary for optimum results.
USING THE LDX-3200 CURRENT SOURCE'S TRIGGER FUNCTION
For applications where you need to synchronously initiate a measurement task from a remote instrument with the
LDX-3200 Current Source, the Current Source offers a trigger output signal. The TTL pulse is initiated with any
remote change in set point of the laser current source. A typical application for utilization of this feature is laser
characterization tasks where an L-I curve is generated. For a programmed step in laser current, a light measurement
can be triggered for each step in laser current. The trigger output is enabled only in remote mode via the IEEE 488.2
GPIB Interface.
The trigger output is available via a standard BNC connector on the rear panel of the LDX-3200 Current Source. See
Figure 5.1. The TTL pulse is approximately 13 µsec wide and has a delay time of about 10 – 12 msec after the current
set point is changed via GPIB. This delay does not include the GPIB transmission time. The time for any command to
be sent via GPIB depends on the interface hardware and software control. The current set point may be changed by
the LAS:LDI, LAS:INC, or LAS:DEC commands.
The minimum step change time required for a corresponding trigger pulse is 20 msec. Care should
be used with respect to the timing of any set point commands in relation to the actual hardware
function. The INC and DEC commands have a minimum step time of about 20 msec which allows
for the hardware initiation of a set point change and the settling of the output. The LAS:LDI
command does not have any fixed delay for settling. With this command, some trigger pulses may
be missed if the program step time is less than the 20 msec minimum.
A one shot trigger pulse will occur on power up of the instrument due to the states of the processor I/O.
FUNCTIONS AND FEATURES
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