Optical focus detecting system and optical recorder-reader including such a system.

摘要

1. Optical detector of the focusing error between the convergence point of a light radiation and a reflecting surface, comprising a semiconductor laser source (1) transmitting this light radiation and illuminating this surface (4) through an objective (8) ; this objective (8) ensuring the focusing of the radiation received from this source (1) ; optical separator means being positioned between this source (1) and this objective (8) for reflecting towards photodetector means (11) the radiation received through this objective (8) from this reflecting surface (4), these photodetector means comprising four elements the sensitive surfaces of which occupy four quadrants, characterized in that this source (1) has a longitudinal astigmatism, an astigmatic lens (7) being placed between these optical separator means (16) and said objective (8) in order to compensate for this longitudinal astigmatism and for introducing an astigmatism of the radiation received through this objective (8) from this reflecting surface (4).