| 摘要 |
PURPOSE:To provide a light beam condensing method and an optical information reader by which a condensing spot can be made small without weakening a light power of a condensed light beam. CONSTITUTION:A phase-shifting filter 1 has a transparent substrate 2 and a phase-shifting thin film 3. The thin film 3 is arranged in an annular shape. Phase-shifted light is condensed by an objective lens 4. This objective lens 4 is divided into two parts of a center part 5 and an annular part 6. Phase- unshifted light of the center part 5 is condensed on a point (a), and the phase- shifted light of the annular part 6 is condensed on an annular ring (b) around the point (a). The objective lens 4 is formed in a continuous shape so that the same phase can be obtained at the (a) and the (b) when light is condensed only by the objective lens 4 without using the filter 1. |
