| 摘要 |
PURPOSE:To permit detection of the absolute position on a recording medium with an optical head and miniaturization of an information memory medium by using an optically specific point provided to a point where information memory is possible as a revolution mark. CONSTITUTION:The optically specific point which generates double refraction is provided to part of the inside circumferential edge in the memory part A of an information recording medium 1 to constitute the revolution mark 2. Laser light from the head receives the double refraction and increases the quantity of the return light when the mark 2 is brought to the position of the optical head by the rotation of the medium 1. The rotating position of the medium 1 is, therefore, detected by detecting the quantity of the return light increasing periodically at every one rotation of the medium 1. There is thus no need for providing a sensor or the like to be exclusively used for detecting the revolution mark and the information memory and reproduction device is miniaturized. |
