| 摘要 |
PURPOSE:To improve the condensing characteristic of a lens by varying the depth of a groove of a grating part in accordance with an interval of the groove. CONSTITUTION:The title lens is structured by forming a grating part 3 on a substrate 1 and providing a reflecting layer 2 on said part. The grating part 3 is formed in a shape of a concentric circle or a concentric ellipse so that an interval of a groove of each grating becomes gradually smaller toward the outside periphery. Depth of the groove of the grating is determined by the interval of the groove of each grating, and the smaller the interval of the groove of the grating is, that is, as it draws near the outside periphery, the deeper the depth of the groove of said part becomes. In this state, from the substrate 1, an incident light beam 5 being a flat wave front is made incident on the grating part 3, and an emitted light beam 6 which has been reflected and diffracted is condensed to a focus 7. In such a way, even in the outside peripheral part of the lens, a micro-Fresnel lens having a high efficiency and a satisfactory condensing characteristic can be realized. |
