An optical tracking system is presented which aligns a recording head with
a magnetic tape. The system relies on an optically detectable servo track
on the back of the tape. The servo track is formed by repeatedly
engraving, at spaced intervals, three co-linear marks perpendicular to
the length of the tape. Laser light reflects off the marks, and passes
through a ball lens that directs the reflected light on to separate light
detectors, one for each mark. By recording characteristics of the
reflected light, the detectors transmit information to the system that
permits the recording head to be properly aligned with the tape.