Optical head with provision for tracking and focussing control

摘要

An optical head for reading a signal recorded along spiral or concentric tracks on an optical disc including a semiconductor laser for emitting a linearly polarized light beam, a polarization prism for transmitting the light beam, an objective lens for projecting the light beam upon the optical disc and for collecting a light beam reflected by the optical disc, a critical angle prism for totally reflecting the light beam reflected by the polarization prism and a light detector for receiving the light beam totally reflected by an optical surface of the critical angle prism. The polarization prism and critical angle prism are integrally coupled with each other to form an assembly of prisms which is rotated to adjust an incident angle of the light beam impinging upon the optical surface of critical angle prism substantially at a critical angle of total reflection.