| 摘要 |
PURPOSE:To miniaturize a pick-up, by condensing a part of laser beam by the parabolic surface reflective mirror shaped part of an iris lens holder and detecting the difference signal of a quadrant light receiving element positioned in the vicinity of the focus thereof to measure surface deviation and core deviation. CONSTITUTION:The end surface (a) of an iris lens holder 8' in a laser beam source side is processed to a parabolic surface reflective mirror shape so that the axis of reflected light as an angle to the axis of incident light and a part of laser beam is reflected from the end surface (a) and condensed to the focus (b) of reflected light. When pick-up is allowed to follow the recording groove of a disc 7, the holder 8' performs parallel motion in a focus direction (e) and a tracking direction (f) along the recording groove and the difference signal (Valpha+ Vbeta)-(Vgamma+Vdelta) of voltages Valpha, Bbeta, Vgamma, Vdelta detected from the split regions alpha, beta, gamma, delta of the light receiving element 13 is depended only on the displace amount in the focus direction and the difference signal (Valpha+Vdelta)-(Vbeta+Vgamma) is dependent only on the displacement amount in the tracking direction. |
