Lightwave Communications LDX-3232 manual Photodiode Connections, Setting the PD Bias

O P E R A T I O N

Connecting to the Laser

Photodiode Connections

C H A P T E R 2

Many laser diode modules contain an internal photodiode that monitors the back- facet emission of the laser. Usually, this photodiode is internally connected to either the laser anode or cathode.

The photodiode and laser connections to the LDX-3232 are electrically isolated from ground and each other. So, if a 4 pin connection is made (no common connections), no additional jumpers are required. Figures 2.1 - 2.4 show the recommended connections and shielding for 3-pin lasers (where the common connection is internal to the device). A 4-pin laser should be connected with the same shielding as shown in Figure 2.1, but the common connection (between the photodiode and the laser) is optional.

Setting the PD Bias

The LDX-3232 provides an adjustable reverse bias of 0-5 VDC for the photodiode. To set the photodiode bias to 5 V reverse bias, turn the back panel PD BIAS ADJUST fully clockwise. To set the photodiode bias to 0 V reverse bias, turn the back panel PD BIAS ADJUST fully counter-clockwise.

Grounding Considerations

The LASER outputs of the LDX-3232 High Compliance Current Source are isolated from chassis ground, allowing either output terminal to be grounded at the user's option. Figures 2.1 - 2.4 show the proper earth-ground shielding for laser diode/photodiode connections.

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