I?m trying to find as much information as possible about the design
and use of reflective optical encoders including shaft angle encoders.
 Specifically, I need information about devices that have a light
source and a detector on the same side of a rotating disk that bounce
light off the disk to the detector.  I don?t need to know about the
kind that shines light through slits in a disk. The information
doesn?t necessarily have to be available online.  Most helpful would
be something like an identification of textbooks or maybe detailed
journal articles that explain how these things work.  Ideally, some of
the information would come from around the time these devices first
started to be used and also later stuff to help me track the
development of various features so that I can possibly figure out how
they can be improved.

They work like barcode scanners and are called absolute encoders. A
micro controller strobes a LED to transfer the image of the bar code
to a linear optical array. The micro controller then decodes the
signal from the array and finds the current position.