Abstract: The present invention provides an optical device comprising a pair of specifically designed plate-like diffractive optical elements successively arranged in parallel to each other. Placing the two diffractive optical elements in succession and in parallel to each other in a certain distance, the combination optically corresponds to a single diffractive optical element, and it can perform similar tasks, acting as a lens, an axicon, a phase shifter, or a spiral phase plate. If one of the diffractive optical elements is rotated with respect to the other around a common central axis, the property of the optical device, like the focal length, the refractive power, helical index, or phase shift changes continuously.

Abstract: The present invention provides an optical device comprising a pair of specifically designed plate-like diffractive optical elements successively arranged in parallel to each other.,. Placing the two diffractive optical elements in succession and in parallel to each other in a certain distance, the combination optically corresponds to a single diffractive optical element, and it can perform similar tasks, acting as a lens, an axicon, a phase shifter, or a spiral phase plate. If one of the diffractive optical elements is rotated with respect to the other around a common central axis, the property of the optical device, like the focal length, the refractive power, helical index, or phase shift changes continuously.