Extension of Zone Plate and Its Application

The Fresnel zone plate is extended, and its application to synthesize optical images is presented.First, the fixed-width zone plate is introduced. It is a modification of the Fresnel zone plate conventionally used, and has a simple shape easy to produce. The effect of modification is discussed. Then a method to produce the extended zone plate which can focus not only an image of point but also an image of curve is presented. The extended zone plate of fixed width is used in the form of off-axis. This zone plate gives an image with good contrast, and the time to produce the zone plate is saved very much. The required image is obtained as the sum of partial images which are gotten by using the extended zone plate. Several examples of the images synthesized by this method are shown.Moreover, the 3 D-extended zone plate and the color extended zone plate are proposed to synthesize a continuous three-dimensional image and a color image, respectively.The zone plate has been drawn by the computer controlled drafter on a paper, and then photoreduced for production.