Fabrication and properties of refractive micro-optical beam-shaping elements

Several algorithms can be used in order to calculate a phase function that shapes a light beam into a certain intensity distribution. In cases of smooth phase functions, e.g. for the conversion of a Gaussian beam into a flat top distribution, the optical element can be realized by a smooth surface profile without 2 pi jumps. Even though the disadvantages of diffractive elements are well known, often the limitations of the fabrication technologies permit the realization of only diffractive elements. For the beam shaping elements in micro optics, methods exist which allow the fabrication of smooth surface profiles. Such refractive elements have the advantages of a wavelength independent behavior and a conversion efficiency of nearly 100% as known from refractive lenses. In some cases, the design of refractive result in thick surface profiles and the fabrication technique do not fit to this. Therefore, the objective of the paper is to show some possibilities to make the design meet the fa brication capabilities. We used lithographic and etch techniques as well as replication technologies for the fabrication. The basis of the presented technology is gray tone technique, the generation of a proper pre-form, and its correction in order to achieve maximum coincidence with the desired surface profile. Several refractive beam shaping elements have been realized.