Control Modes - Newport 6100 User Manual

Principles of Operation
6.4.2

Control Modes

The Model 6100's Laser Diode Driver subsystem operates in one of two
control modes – Constant Current Control Mode or Constant Power Control
Mode. Following power-up, the unit always will be in Constant Current
Control Mode. The user may then change to Constant Power Control Mode
using the LAS:MODE command via the USB interface. See Section 5.5 for
more information on this command. It is not possible to change the operating
mode from the front panel of the unit.
Operating mode is not retained in the unit at power down. This means that
the unit will always power up in Constant Current Control Mode.
6.4.2.1 Constant Current Control Mode
In Constant Current Control Mode the Laser Diode Driver subsystem will
servo its output current based on output current measurements it makes.
6.4.2.2 Constant Power Control Mode
In Constant Power Control Mode the Laser Diode Driver subsystem will
servo its output current based on the current through the attached laser
diode's back-facet diode.
6.4.2.3 MODULATION Input
The Modulation Input allows the modulation of the laser diode by an external
signal source through the BNC input, which is a differential input. The
output current level to the laser diode can be set using an external voltage
source, or it can be modulated with a function generator signal. Any input
modulation signal is added to the DC drive current level set by the front panel
control knob. A bandwidth selection switch on the back panel introduces a
dampening filter in the output control loop to reduce the output noise when
external modulation is not required. If the output drive current does not
respond to a modulation frequency above 10kHz, check the switch to make
sure it is not in the LOW bandwidth position.
When using the current modulation feature, ensure that the
modulation signal source is disabled before enabling the 6100
laser current output. Turning on the laser current output when
the modulation is enabled can cause current transients that can
damage laser diodes.
WARNING
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