| 摘要 |
PURPOSE:To reproduce optical information by optical pickup in an excellent way by using a reflection type diffraction grating image forming lens so as to use a separating function of an incident light and a reflected light and a function of an astigmatism optical diffraction grating in common and adding a function of a reflecting mirror reflecting the optical path. CONSTITUTION:A 0-th order diffracted light not diffracted by a reflection type diffracted grating engraved on the surface of a lens 16 is collected as a spot being a diffraction limit on an information recording face 10 via an objective lens 18 among the lights made incident on the reflection type diffractive grating 16 of the lens 20 from a laser diode 1. The reflected light at that point is converted into a light taking the radiated point of the diode 1 as an optical converging point and made incident on the grating 16. The light made incident on the grating 16 is separated into luminous fluxes 23, 24 by image forming lenses 16a, 16b and a focus error signal is obtained by placing a 4-split photodetector 20 at a light converging position of the luminous fluxes 23 and 24. |
