S. Komatsu: Extension of Depth of Focus by Wavefront Coding, OPTICS DESIGN, Vol. 42, 3-6 (2009).

Wave-front coding (WFC) is well-known as an efficient technique for extending the depth of focus of an imaging lens. The WFC technique requires a phase mask to modulate the pupil function as well as the corresponding post image processing for decoding. The principle of WFC is reviewed from alternative physical standpoints. In addition, to achieve a further extension of the depth of field, we propose the use of a free-from phase mask (FPM) instead of a conventional cubic phase mask (CPM). We optimized the shape of the FPM using the simulated annealing algorithm and confirmed that the optimized FPM provides a much larger focal tolerance and better final images than the CPM. Results of optical experiments achieved with a fabricated FPM are presented in the talk.