Lab-Grade LD & TEC Drivers

If you don’t feel confident enough to make the custom LD & TEC drivers circuit yourself, you can rely on Thorlabs LD & TEC drivers.

All the following instructions refer to the Thorlabs drivers LDC205C and TED200C that I was formerly using in the breadboard version. These drivers can be purchased either as part of the LTC56A/M kit or separately. When purchasing the drivers separately, you will also need a CAB400 cable and a CAB420-15.

The cables CAB400 and CAB420-15 are however too rigid to be set in place directly in the setup. You will have to make an extension to those cables like in the picture on top of this page.

Soldering the cables is not difficult but you will need a soldering iron, some lead-free solder, cables, and two pairs of SUB-D9 connectors (2 males and 2 females). You may also want to use some flux and heat-shrinkable tubing to achieve top-quality.

Thorlabs provide drawings of the pinout of their LDM21 part. The pins on your SUB-D9 connectors should be labeled accordingly. Double-check your connections if you don’t want to damage either your LD, LDM21, or drivers!

The overall concept is to connect the pin 1 or the male SUB-D9 connector to the pin 1 of the female SUB-D9 connector and so on. The male/female pinouts should be mirror images of each other. Use colored cables to avoid mistakes when connecting the cables and keep the cable length to 20 cm maximum.

I recommend twisting the pairs 3-7 for the LD controller and the pairs 2-3, 4-5 and 7-9 for the TEC controller. Twisting will help in having more stable signals, especially on high impedance inputs such as the thermistor.

Use 0.7 mm wires at the very least and 1.0 mm wires for the pairs 4-5 of the TEC driver as it may have high currents flowing through. When using Thorlabs drivers, I recommend connecting all cables except those marked as N.C. in the pinout drawings of the LDM21.

When operating the laser, always start the TEC driver first with a temperature set point to around 22.50°C. Once the temperature is stable, turn on the laser and gradually increase the current. If you don’t have a power meter to control the actual output of the laser, I recommend not exceeding 300 mA for the LD.

Note that the LD output is strongly influenced by the temperature so it is mandatory to keep the TEC driver steady when performing your recording. In my experience, the LDM21 should regulate your LD at 300 mA to 22.50°C as long as the ambient temperature does not exceed 5°C from the set point. I have had some issues in the summer with that so be sure to install your setup in a room with a controlled temperature.