| 摘要 |
PURPOSE:To prevent the generation of a track offset by combining a simple grating that divides the light received from a light source into two secondary beams having different directions from a primary beam and a grating lens that divides the primary beam into two beams and leads them to a photodetecting surface of a photodetector together with said two secondary beams. CONSTITUTION:The radiated light 2 of a semiconductor laser 1 is diffracted into three beams 31-33 by a simple grating of a double grating lens 26 and focused onto a disk surface 4. When the primary beam 31 is projected on a track, the secondary beams 32 and 33 are set as if they held a track and the working of the track is detected as the intensity change of the reflected light. The reflected light received from the surface 4 is diffracted by the lens 26 and made incident on a 6-split photodetector 27. Thus the beam 31 is divided into two beams by the grating lens as the diffracted beams 18 and 19. These beams 18 and 19 are used by the photodetecting elements 11-14 to detect a focusing error and a reproduction signal. While the beams 32 and 33 are made incident on the tracking detectors 29 and 30 and the difference signal between these detectors means a tracking error. Thus it is possible to obtain a compact optical head device which is free from the offset of the tracking error signal. |
