| 摘要 |
PROBLEM TO BE SOLVED: To give a converging function required for making a diffraction optical element compact by using a divergence type CGH element having a converging point and a virtual image point for at least one CGH element (computer hologram) giving a converging point. SOLUTION: For at least one CGH element 10 giving a converging point, a divergence type CGH element having a converging point and a virtual image point is used. When spherically divergent ray from an object point (convergent point: X, Y, Z) is made incident to the CGH element 10 at a cetain divergent angle, it transmits the CGH element 10, and the transmitted light is emitted toward the opposite side of the object point, i.e., the convergent point side, i.e., the other side of the CGH element. By straightly tracing the locus on the outgoing light side of the divergent light transmitted through the CGH element 10 to the convergent point side on the incidental side, i.e., the object point side, the virtual image point (X, Y, Z on the object point side is obtained. Hereby, in the transmission-divergence type CGH element 10, the object point (convergent point) and the virtual image point exist on the same side in view from the CGH element 10. Consequently, the converging function is shared by a plurality of the CGH elements 10.
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