Fiber Coupled Laser Source
Chapter 5: Operation
Page 8
2288-D02
5.6. Modulating the Laser Output
The MOD IN input can be used to modulate the laser output, or set the laser output remotely using a +5 V power
source. The 5 V maximum input corresponds to the maximum calibrated power of the S3 Series DFB Laser
Sources, which operate using a constant current drive technique and causes the actual output power to be
dependent on the set operating temperature. That is, for a modulation input of 5 V the output power will vary
depending on the operating temperature. In addition, in order to eliminate a dead zone in the power control knob,
the output of the unit is offset to the threshold current of the coupled laser diode. Therefore, when the PWR ADJ
knob is full counter clockwise, the drive current is not zero but actually at the threshold current. This should be
kept in mind when using the modulation input.
1.
Connect a signal generator or 0 to 5 V power source to the unit using a BNC type connector.
2.
Set the PWR ADJ knot on the front panel to its full counter clockwise setting.
3.
Press the ENABLE switch to turn on the laser, wait for the safety delay to time out.
4.
Apply the appropriate signal to the MOD IN input. Signals above approximately 5.5 V will be clamped by
internal circuits.
5.
Adjusting the PWR ADJ knob will allow for a DC offset on the modulated output. Adjust the input signal
accordingly to avoid clipping the output waveform, which will occur if the unit is driven to its current or
power limits.
CAUTION
DO NOT apply TTL or square wave modulation to the MOD IN input. Due to response delays of the
constant power control loop, damage to the integrated fiber coupled laser may occur!
