| 摘要 |
PROBLEM TO BE SOLVED: To stabilize performance of an optical head by satisfying prescribed relations in such items as a distance between a light emitting element and a diffraction element, a distance between the diffraction element and a converging element, the maximum effective diameter of the converging element, an angle of diffraction in the diffraction element, and the width of a diffraction region in the diffraction element, and thereby inexpensively reducing stray light due to outward diffraction light. SOLUTION: The reflected light once reflected by an information recording medium and again passed through a converging element is diffracted, with its ± primary diffraction light guided to a light receiving element. In this case, assuming a distance between a light emitting element and a diffraction element is a, a distance between a diffraction grating element and a converging element is b, the effective diameter of the converging element is D, an angle of diffraction in the diffraction element is C, and the width of a diffraction region in the diffraction element is d, the relation of the expression is to be satisfied. Under such conditions, there is no possibility that the diffracted light diffracted in the hologram region 6 outward enters the effective diameter D of an objective lens 3, converging on an information recording medium 4, and that its reflected light again passes through the objective lens 3 and the hologram region 6, making incident on photo-diodes 2a, 2b, becoming stray light and mixing in the original information signals. |
