Lightwave Communications LDX-3232 manual Modulating the Laser Current Source

FUNCTIONS AND FEATURES

Modulating the Laser Current Source

C H A P T E R 5

Setting up the Current Source for a modulated laser injection current is easy. The (MOD) EXTERNAL connector (BNC) on the front panel is the input for the modulated signal. Connect a modulating voltage signal from a standard function generator, for example, to this connector. The modulation port input impedance is 1 kΩ. The transfer function for the low and high current ranges of the LDX-3232 are 200 mA/V and 400 mA/V.

Set the LDX-3232 in Constant Current High Bandwidth Mode by selecting IHBW in the MODE section of the front panel. Do this by toggling the (MODE) SELECT push button until the IHBW indicator is illuminated. Repeatedly pressing the (MODE) SELECT switch cycles through the current (I), optical power (P), or high bandwidth current (IHBW) control modes.

Next, set the current source range by selecting the

2000 mA range indicated by the accompanying LED. You will need to press the select push button twice to change the range. It must be pressed twice quickly (within less than one second) to switch between modes, and the current source output must be off (MODE ON indicator unlit) in order to change ranges.

The limit clamp function for DC output current applies to the modulated current as well protecting your laser in any mode. To accomplish setting the current source limit, use the (PARAMETER) SELECT push button LIM I. Press the (PARAMETER) SET push button and rotate the adjust knob. Set the limit to 1750 mA. Once the (PARAMETER) SET push button is released, the new parameter value is stored in non-volatile memory.

When the laser current limit is reached, the CURRENT LIMIT error indicator flashes. The current limit setting is independent of the voltage drop of the device connected to the laser output, and therefore, no dummy load is required for precise adjustment of the current limit. Furthermore, since the current limit circuitry is fully independent of the main current control, the current limit can be adjusted safely, even while the current source output is active.

Now you are ready to modulate the laser injection current. To enable the Current Source output, press the push button labeled (MODE) OUTPUT. The accompanying LED labeled ON will illuminate indicating that the laser current source's output is enabled. The instrument will drive the current source to the value set by the corresponding MODE setpoint. Turn on the function generator (modulation source) to inject the modulation signal.

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