| 摘要 |
<P>PROBLEM TO BE SOLVED: To obtain an objective optical system for an optical recording medium capable of efficiently converging used light on two or more optical recording media having almost similar wavelengths of the used light and different substrate thicknesses. <P>SOLUTION: Sequentially from a light source, the objective optical system comprises a refractive power variable element 18, a diffraction optical element L<SB>1</SB>with a diffraction optical surface at least on one surface, and an objective lens L<SB>2</SB>having positive refractive power. In the OFF state of applied voltage, the refractive power variable element 18 functions as a transparent flat plate without a convergence function, but on the OFF state of the applied voltage, the refractive power variable element 18 consists of liquid crystal elements which function as a convergent lens. When AOD9a, DVD9b, and CD9c are selected, the refractive power variable element 18 is made into the state in which it does not have refractive power, and when BD9d is selected, the refractive power variable element 18 is made into the state in which it has positive refractive power. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
