Rotary Pulse Generators ?

Hello to all;
These where advertised as 2 channel RPG's, with IR emitter and
photo logic detectors which output 5v logic level.
My question is what are they, and can they be used like encoders?
they have what looks like an encoder wheel inside. if i look close
through the two holes in the case i can see the slots in the disk,
one set seems to be coarse and the other set seems to be fine, theirs
a small circuit board with the transmitters and receivers with a
resister and capacitor and looks like maybe a couple of trimmer pots,
(assume for adjusting the sensitivity), and four wires red, black,
orange and brown, assume red and black power and ground, and brown
and orange the two channels.
Thanks to all the people on this site for sharing all there valuable
info.