Some build progress. The alignment stage. The semitransparent mirror was taken from a CDROM optical head. Its thickness is about 2 mm, which I find being way too thick for the purpose, but I have not found anything else yet.

And I've found a good source of tiny optoendstops - a digital camera. There are 4 in there. Brilliant!

This version of the sensor looks too large to be embedded, so I'm making it for the mere purpose of getting a working sensor. Once I get it, I'll build another one as small as I possibly can.