Analog Modulation - THORLABS EK2000 User Manual

OEM Laser Diode Driver Evaluation Kit
5. Short P10 on the Eval Board to set analog modulation to FULL ON
(factory default setting).
6. Short P9 on Eval Board to set ON/*OFF to off position (factory default
setting).
7. Turn both the PD Current Trim pot and the Current Limit Trim pot
counter-clockwise 20 turns each to set these at their minimum operating
points.
8. Turn the DC power supply on and use a voltmeter to monitor the LIMIT
OUT (P8 on Eval Board).
9. Adjust the Current Limit Trim pot clockwise slowly while observing the
LIMIT OUT to set the maximum operating current for your laser (refer to
laser manufacturer's data sheets). Note: this output is 40mA/V.
10. Remove the shorting jumper across P9. Using a calibrated power meter
to monitor the diode laser output, slowly adjust the PD Current Setpoint
trim pot clockwise to obtain the desired operating power level. The laser
will begin to emit upon reaching the drive current threshold.
3.1.3.

Analog Modulation

To operate the EK2000 analog modulation feature, follow the setup procedures
for CW Operation to establish the laser operating conditions. Once the EK2000
has been setup for your laser, remove the shorting jumper from P10 and apply a
positive voltage from P10-VMOD to P10-GND to modulate the laser.
1. The analog modulation voltage has a negative transfer function
characteristic. That is, at 0 volts, the laser is fully on, at 2.5 volts the
laser should be fully off.
2. The linear operating range of the analog modulation is determined by
the transimpedance gain of the PD Amplifier, R F . The appropriate
transimpedance gain for your laser can be calculated as follows:
Where I
manufacturer for the maximum operating output power. Note: the
LD2000R includes an internal 20K resistor. R F is the net resistance of
the internal 20K resistor with any external resistance added in parallel
on pins 8 and 12. To calculate the external resistance (R
operate at a particular monitor current (I
Page 7
is the photo diode current specified by the laser
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Chapter 3: Description
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Rev F, May 21, 2018