Lightwave Communications LDX-3232 manual Operating a Laser in Constant Power P Mode

O P E R A T I O N

Operating a Laser in Constant Power (P) Mode

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 (IHBW) 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.

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