| 摘要 |
PURPOSE:To miniaturize a focal error detecting device and make the operation of the device easier, by forming three light spots on a recording medium through a diffraction grating and detecting a luminous flux with two optical detectors by + or - primary diffraction light cut of three kinds of convergent luminous fluxes of the reflected lights. CONSTITUTION:A light emitted from a light source 7 becomes a parallel luminous flux by means of a lens 8 and diffracted by a diffraction grating 9, and then, forms three light spots of zero degree and + or - primary diffraction light on a recording medium by means of a lens 2. Their reflected lights retrogress and are reflected by a beam splitter 3 and condensed by a lens and the + or - primary convergent luminous fluxes are made to incident to optical detectors 12b and 12c. Each of the optical detectors 12b and 12c is composed of a central part 12d and 12f, whose area is smaller than that of the primary convergent luminous flux, and peripheral part 12e and 12g. When the output of the central parts 12d and 12f is differential-amplified, a focal error signal is obtained and, when the outputs of the central part 12d or 12f and peripheral part 12e or 12g are respectively added to each other and the difference between them is obtained, a tracking signal is obtained. Therefore, the device can be miniaturized and the operation of the device becomes easier. |
