| 摘要 |
PURPOSE:To form the titled device to a thin shape by constituting it so that a separating action of an incident light and a reflected light, an action of an astigmatism optical grating lens, and an action of a reflecting mirror for curving an optical path can be executed by one piece of a reflection type diffraction grating lens. CONSTITUTION:Among light beams which are made incident on a reflection type diffraction grating lens 16, a 0-th order diffracted light which is not diffracted by a reflection type diffraction grating carved on the surface of this lens 16 is made incident on an objective lens 18. The objective lens 18 is provided so that a light emitting point of a semiconductor laser 1 is an object point, and a point on the surface of a disk is an image point, therefore, the 0-th order diffracted light 17 which is made incident on the objective lens 18 is condensed as a condensing spot 19 of a diffraction limit onto an information recording surface 10 on the disk 9 from the objective lens 18. A primary diffracted light or a -1st order diffracted light of the reflection type diffraction grating lens 16 is divided into two by the first reflection type diffraction grating lens 16a and the second reflection type diffraction grating lens 16b, and thereafter, converted to a first luminous flux 23 and a second luminous flux 24, which are condensed to a 4-split light detector 20. |
