Lightwave Communications LDX-3232 manual Modulating the Laser Current Source

C H A P T E R 5

FUNCTIONS AND FEATURES

Using the LDX-3232 Current Sources’s BNC Interlock Connection

Using the LDX-3232 Current Sources’s BNC Interlock Connection

The LDX-3232 BNC interlock connection is designed to allow an external emergency input signal to turn the current output off. The BNC interlock is TTL compatible and configured to be normally closed (as opposed to the DB-9 interlock connection, that is normally open). The BNC interlock connection, when left unconnected, is pulled to a logic high with a 100 kΩ resistor. High values

(+5 V) will keep the interlock closed (current source in the operational state), while low values (0 V) will open the BNC interlock (forces the output off). Once the BNC interlock is opened, the output will stay off until the interlock is closed again, and you re-enable the output.

BNC Interlock Usage Example

When using the LDX-3232 Current Source to drive a temperature controlled laser diode, the BNC interlock can be used to accept an error signal from the laser diode temperature controller unit. Linking the LDX-3232 Current Source to a temperature controller* with the ability to signal when its temperature control has gone outside of some tolerance window will allow the LDX-3232 to safely shutoff its output before thermal damage occurs to the laser diode.

*The ILX Lightwave LDT-5900 series of temperature controllers include an output BNC connector that is compatible with the BNC interlock feature of the LDX-3232. The output BNC connector of the LDT-5900 has a TTL compatible output signal that will signal when the temperature control has gone outside of a programmable temperature window. For more information about the LDT-5900 series of temperature controllers, please call 1-800-459-9459 (USA or Canada only), 1-406-556-2481 (International), or go to www.ilxlightwave.com.

Modulating the Laser Current Source

The LDX-3232 Current Source allows a modulated signal to be superimposed on the source output current. For example, assume you are using an LED for your experiment where you need to operate the LED in constant current at POP =

100 mW, with a modulated signal from 3 to 30 kHz. The experiment requires the LDX-3232's laser Current Source to be configured for the 2000 mA range, high bandwidth mode with a limit of 1750 mA. The allowable bandwidth of the modulated analog signal, defined as the 3 dB roll off point, is dependent on the output current range and the mode (constant current low/high bandwidth). See the section, LASER CURRENT SOURCE SPECIFICATIONS, in Chapter 1 for external analog modulation bandwidth specifications.

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