| 摘要 |
PURPOSE:To obtain a small-sized optical head device without necessity of sticking surfaces and free from positional adjustment by assigning the astigmatism to the specific plane of a polyhedron optical element of one substance. CONSTITUTION:A luminous flux 2 from a laser beam source 1 irradiates the track 11 of a disk 8 through a lens 7 as three light spots 12a, 12b, and 12c after the luminous flux is separated into two parts by the diffraction grating 16a of a prism 16 and reflected by the total-reflecting mirror surface 16b and half-mirror surface 16c of the prism 16. Reflected rays of light are made incident on elements 14a-14c of a detector 14 as beams 15a-15c almost parallel with the emitted luminous flux 3 through the lens 7 and a reflecting mirror surface 16a. When the beams 15 are passed through the half mirror surface, astigmatism is given to the beams 15, since the beams 15 are transmitted through the half mirror surface after the beams 15 are obliquely refracted. Since the prism 16 is produced by cutting a parallel planar glass into a parallelogrammic shape having a vertical angle of 45 deg., the prism has no sticking surfaces and no unnecessary aberration is produced in the prism. When such a constitution is used, a small-sized optical head which is reduced in the number of constituents and assembling man-hour can be obtained. |
