O P E R A T I O N S
Functions and Features
7/01
LDC-3700 Series
33
C H A P T E R
2
indicator is illuminated. Repeatedly pressing the (
LASER MODE
)
SELECT
switch cycles through
the current (
I
), light power (
P
), or high bandwidth current (
I
HBW
) control modes.
Set the laser controller’s current source range by selecting the 200 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 1 second) to switch between modes, and the LASER
output must be off (LASER 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
SELECT
push
button in the
PARAMETER
/
LASER
section of the front panel to select
LIM
I
. You will notice there
are two
LIM
I
selections, one in blue text and the other in black text. These limit selections
correspond to the current source range as indicated in the
RANGE
section. When the blue
LIM
I
is
indicated by the accompanying LED, the
LASER
display will be indicating the limit set point in mA
for the controller’s low range. Press the (
PARAMETER
)
SET
push button and rotate the adjust
knob, clockwise to increase the limit set point value, or counterclockwise to decrease the limit set
point value. Set the limit to 175 mA. Once the
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
LASER
output is active.
Now you are ready to modulate the laser injection current. To enable the controller output, in the
LASER
MODE
section of the front panel, press the push button labeled
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
LASER
MODE
set point . When the
LASER
output is off, an internal short is placed across the laser output.
ON
OUTPUT
I
HBW
P
I
SELECT
LASER MODE
PRESS TW ICE
2 0 0 mA
5 0 0 mA
RANGE
LIM I
TE
SAVE
CONST
GAIN
LIM T
HI
TEC
LIM I
CAL PD
LIM I
LIM P
RECALL
SET
SELECT
PARAMETER
LASER
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