| 摘要 |
PURPOSE:To enable the size of minute spot light on a recording medium to be always maintained at the size optimum for recording and reproducing by providing a means of varying the distance between aperture lens and recording medium. CONSTITUTION:Focus controlling is accomplished by moving an aperture lens 7 in the arrow Z axis direction so that the respective quantities of receiving light of photo detectors 13, 14 become always equal. If the photo detectors 13, 14 are moved in the Y-axis direction while performing focus controlling, the distance between the aperture lens 7 and disc 10 may be selected as desired. When a disc 10 is placed in the optimum recording position, it turns out that the imaging position of the aperture lens 7 is above the disc 10, and the quantity of reflected light to be fed back to a semiconductor laser 1 of that time becomes maximum. |
