| 摘要 |
<P>PROBLEM TO BE SOLVED: To solve the problem that an excessively high detection sensitivity narrows a focus pulling range, especially the larger NA of an objective lens increases detection sensitivity, consequently, strict assembling accuracy is required, or focus is easily shifted due to vibrations or shocks, thereby causing unstable focus servo when a knife edge method is used as a method for executing focus servo of an optical head. <P>SOLUTION: A luminous flux from a light source 2 becomes a parallel light at a coupling lens 5, and directed to an objective lens 9 by a rising mirror 7 without being affected by a luminous flux conversion means 6 including an optical anisotropic material. A luminous flux converged on the surface of an optical recording medium 10 becomes a parallel light through the objective lens after reflection. The polarizing direction of the reflected light is rotated by 90 degrees by passing through a 1/4 wavelength plate 8 twice, and receives a lens operation by a luminous flux conversion means 6. From the luminous flux conversion means 6, a parallel light having a luminous flux diameter reduced is emitted, and NA is converted to be small by a combination with a coupling lens. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
