Operating a laser in constant power (p) mode – Lightwave Communications LDX-3232 User Manual
Page 33
O P E R A T I O N
Operating a Laser in Constant Power (P) Mode
04_06
LDX-3232
17
C H A P T E R
2
Conditions That Will Automatically Shut Off the LASER OUTPUT
The following conditions will automatically cause the instrument to disable the
current source output:
• LASER High Power Limit
• LASER Interlock / Key Lock Turned Off
• LASER Open Circuit or Voltage Limit
Operating a Laser in Constant Power (P) Mode
Suppose you want to operate a 3 mW laser at constant 1mW level. The LDX-3232
allows you to operate the laser current source driver in a Constant Power mode.
In this mode, the LDX-3232 drives current to the laser to reach a setpoint power
value (in mW). The control loop feedback parameter is photodiode current that the
LDX-3232 converts to optical power via a user-defined photodiode responsivity
number. If laser power changes due to internal or environmental conditions, the
LDX-3232 will increase/decrease the current to the laser to maintain the power
setpoint. The following paragraphs detail the instrument configuration in Constant
Power Mode.
To set the LDX-3232 in Constant Power mode, select P in the MODE section of
the front panel by toggling the SELECT push button. Repeatedly pressing the
(MODE) SELECT switch cycles through the current (I), light power (P), or high
bandwidth current (I
HBW
) control modes. The LED indicator shows the selected
mode.
Entering Photodiode Responsivity Values
The photodiode responsivity, CAL photodiode, is
used to convert between photodiode current and
optical power of the laser diode. To enter the CAL
photodiode parameter, select CAL PD with the
(PARAMETER) SELECT push button by toggling
down past LIM P. The indicator becomes lit when
CAL PD is selected and the display indicates the
responsivity parameter in µA/mW (not an-
nunciated). Rotate the adjust knob while holding the
(PARAMETER) SET push button to enter a new
value for responsivity. When the correct value is
displayed, store the number by releasing the
(PARAMETER) SET pushbutton.