Analog Modulation Input - THORLABS ITC502 Operation Manual

2.16 Analog modulation input

2.16 Analog modulation input
The laser diode controller ITC5xx has an input to modulate the laser diode current in
constant current mode.
As the internal set value for the laser diode current is modulated all laser protections
remain active (!).
The modulation input is designed for input voltages between -10V ... 10V and
specified for small signal operation. In large signal operation the 3 dB bandwidth is
reduced. (See datasheet for version dependent bandwidth)
Commonly you will select a DC current with the main dial knob and modulate this
current with the modulation input. Please note that this DC current and the
modulation current are added, so you will use a modulation voltage without a DC
share!
The modulation coefficient is version dependent.
(See chapter 1.5, "Technical Data" starting on page 7)
As modulation source you can use any commercially available function generator or
any signal source with output voltage in the specific range.
NOTE
Over-modulation is defined as producing a set value for the laser diode
current of below 0 mA, above the limit value or above the maximum
current your ITC5xx can deliver.
To guarantee a proper operation of the ITC5xx please avoid over-
modulation because it can lead to overshoots in the laser current.
If you are uncertain please try with a high current rectifier instead of the
laser diode and watch the analog output. You should never see
overshoots!
ITC500 / page 48