RECORDING AND REPRODUCING OPTICAL PICKUP USABLE FOR DISKS OF DIFFERENT THICKNESS

PROBLEM TO BE SOLVED: To make disks having different thickness interchangeably usable. SOLUTION: A transparent plate 2 which has an area forming thereon a diffraction grating pattern to diffract light going to an objective lens 5 from a light source 1 and a transparent area which transmits the above light therethrough, and a photodetector 9 which has a first and second light receiving parts, are provided. On a thin disk 6, zero-order transmission light and transmitted light are converged by an entire aperture area of the objective lens 5, and on a thick disk 7, plus 1st order diffracted light beam is converged by a part of the aperture area of the objective lens 5. This reflected light is detected by the first and second light receiving parts. Since a signal for reproducing and servo to each disk is detected as a detection signal of the first and second light receiving parts, a stable servo and a noiseless reproducing are enabled irrespective of thickness of a disk used.