| 摘要 |
PURPOSE:To obtain an optical head by which the aberration of a lens due to the change of temperature and humidity can be corrected, by providing an optical path length varying means which varies an optical path length between a light source and the above stated lens. CONSTITUTION:A wedge-shaped glass plate 6 is provided at an intermediate position between a semiconductor laser 1 and a plastic objective lens 2. By designing the plastic objective lens 2 as the one to which a glass plate having a thickness of (t) is inserted from the first, and changing the thickness of the glass plate by thickness of 8t, the optical path length from the light source 1 to the plastic objective lens 2 varies by 8t(n-1). Where, (n) is the refractive index of the glass plate. Therefore, by inserting or pulling out the wedge-shaped glass plate 6 in a direction orthogonal to the optical axis of the plastic objective lens 2, it is possible to vary the optical path length between the semiconductor laser 1 and the plastic objective lens 2. In this way, it is possible to always hold the aberration in the best state. |
