Abstract: The principle of curved grating with gradually changing periods is presented. Its diffraction characteristic and imaging characteristic are analyzed. The result shows that curved grating with gradually changing periods has dual effect of beam splitting and focusing. The symmetrical diffraction level has effect of positive lens and negative lens, and the focal length is equal. It focus the objects of different depth of field and image the same focal plane with space separating.

Key words: curved grating with gradually changing periods, diffraction characteristic, imaging characteristic