| 摘要 |
PURPOSE:To attain efficient and effective signal detection by leading a laser beam to an optical information recording medium, separating the reflecting light into transmission light and diffracted light when the information is recorded, and introducing the lights to each detector to satisfy the specific conditions. CONSTITUTION:A laser beam of a laser light source 13 of a laser light source 13 is shaped, collimated, reflected and collected respectively by a beam shape prism 14, a collimate lens 15, a beam splitter S16 and an objective lens 17, the resulting light irradiates the surface of an optical information recording medium D 18, in which is information is recorded. Moreover, the reflected light from the medium D18 is led to 1st and 2nd diffraction gratings 22a, 22b of a dual grating 22 through the lens 17, the splitter S16 and then via a 1/2 wavelength plate 20 and a detection lens 21 and separated into a transmission light T and a diffracted light K, and the transmitted light is detected by diffracted light detectors 23, 24. In such a case, the detectors 24, 23 are arranged in a position fluctuation allowable area A on the Z axis in which position fluctuation quantities DELTAX, DELTAY on the face of the detector 24 for the light K due to a wavelength fluctuation DELTAlambda satisfy the conditions of equations. Thus, it is not required to overlap the lights T, K and the signal is detected efficiently and effectively. |
