Are you interested in the Moviola particularly, or optical audio in general? If the latter, then http://en.wikipedia.org/wiki/Movie_projector#Optical has a good basic intro to how traditional optical-encoded amplitude modulation works, as well as more modern Dolby Digital / SDDS / DTS digital-optical audio encoding. You may find more luck searching using terms such as "sound-on-film".
Sound Recording Practice (ed. John Borwick) (http://www.amazon.co.uk/Sound-Recording-Practice-John-Borwick/dp/0198166087/ref=sr_1_1?ie=UTF8&qid=1293560292&sr=8-1) has a section on the technology used in audio reproduction for film as well, might be worth looking in your library for.
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