| 摘要 |
PURPOSE:To reproduce independently a signal for each sloping surface by dividing the light of a laser by a diffraction grating to irradiate the -1st order and +1st order diffracted beams to the top and its adjacent bottom parts of an optical disk having V-shaped grooves, and performing the tracking control so that the far viewfield images of both reflected beams are set symmetrical to each other centering on the V-shaped groove. CONSTITUTION:An incident light (a) is divided into 0-th order and + or -1st order beams by a diffraction grating 2 and stopped down to a V-groove disk. The diffracted beams irradiated on an optical disk are reflected on the surface of the V-groove disk and pass through an objective lens 5 and a 1/4 wavelength plate 4 to be separated from the incident light by a beam splitter 3. This separated beam is transmitted through a cylindrical lens 7 and received by a photodetector 8. Here the diffraction gratings are distributed so that the 0-th order and + or -1st order diffracted beams are irradiated on the center, top and bottom parts of the V-shaped groove respectively. The photode tector 8 is divided into three parts for reception of the reflected beams of those 0-th order and + or -1st order diffracted beams respectively. The tracking control is carried out so that the far viewfield images of the reflected light 12 of the + or -1st order beams or the reflected light of the -1st order beam are symmetrical to each other centering on the top M or bottom V of the V-shaped groove.
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