Abstract: A phase mask method to geometrically transform and to optically transfer a standard planar radial grating pattern into a cylindrical photoresist pattern at the circularly cylindrical wall of a given element. The planar radial grating pattern can be written with an integer number of lines having strictly constant period without any stitching problem. The photolithographic transfer is made by an illumination device providing a normal incident beam on the phase mask. The annular radial grating diffracts this normal incident beam, formed by plane waves, into two cylindrical waves of the first diffraction order (T+1 and Tr?1) which impinge on the circularly cylindrical wall and interfere in a photoresist layer deposited on the circularly cylindrical wall to give rise to an interferogram.