Hello,
It is required that the PD gets a beam from the LD and the target simultaneously. Also, there are 2 mechanisms [1] : one depends only on phase interference (this is doable with separate PD and LD). It produces a sinewave-like output that tells the displacement but not the direction of movement. The other relies on that the back-reflected beam from the target passes trough the laser medium before reaching the PD, where it undergoes nonlinear mixing (inside the LD). Its output produces a sawtooth-like waveform, showing both displacement and direction, so it can be fed into a counter, that's we need. Therefore, we'll need an arrrangement where the LD is tapped at both ends, one facing to the target and the other towards the PD (that's what we have with LDs w integrated PD).
Regards,
Ferenc
[1] https://www.spiedigitallibrary.org/journals/optical-engineering/volume-57/is...
On 1/26/22 07:32, David Lanzendörfer wrote:
Hi What about just buying a new cheap Chinese laser diode and a photo diode and then putting a mirror onto the lense carrier, which reflects the laser diode beam back to the photo diode next to the laser diode?
Cheers -lev
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