Tracking error signal detecting device with a two-beam system for use in an optical information memory

Claim 1

A tracking error signal detecting device for use in an optical information memory comprising: means for applying a first light beam spot on a substantially central position of a track formed on an information carrying member and applying a second light beam spot on a position of said track which is spaced from the incidence position of the first light beam spot at least in a direction orthogonal to a direction of tracing of the track; means for independently photoelectrically converting light beams obtained from said first and second light beam spots respectively and modulated by said track; means for effecting envelope-detection with respect to outputs of said photoelectrically converting means to produce first and second detection signals; means for obtaining a difference between said first detection signal and a pre-set first reference value signal to produce an error signal; means for comparing said second detection signal with a pre-set second reference value signal to produce a polarity signal; and means for changing over the polarity of the error signal in accordance with the polarity signal to derive a tracking error signal.