Laser diode current source

A project log for Michelson interferometer

A Michelson interferometer made (mostly) by 3d printing and repurposing components from disassembled optical drives.

andrew-fergusonAndrew Ferguson 10/11/2015 at 18:510 Comments

So far I just implemented the simplest controllable current source circuit that I could find in Horowitz and Hill. I use the Teensy 3.1 DAC output in order to set the voltage on the base of a generic npn transistor. Then Ic = (Vb-0.6)/R, where R is the collector resistor. A better current source will use an op-amp in order to remove the 0.6 V offset and linearise the response. But here is the simple transistor circuit.

By measuring the voltage, with the Teensy 3.1 ADC, across the 10 Ohm resistor it was possible to check if this circuit was behaving as expected. Here is the result which I was pleasantly surprised by. While this circuit lacks many of the sophisticated features (ESD protection, slow start, etc) of a proper laser diode controller, it did allow me to start controllably driving the laser.