Design and Fabrication of Diffractive Microlens and Analysis of Optical Characteristics

摘要

The method for designing diffractive microlens with micro-nano-scale structural features, through iterative angular spectrum algorithm, and fabricating diffractive microlens by single-step photolithography and a wet etching process, based on standard micro-nano-technology, was presented. Surface morphology testing shows that the diffractive microlens fabricated is composed of multi-step continuous relief structures with the feature height in the micrometer range, the distribution of the surface micro-nano-structures is circular symmetry, and the transition between the circular rings is smooth. A large number of fine structures with micro-nano-scale features can be clearly observed in the scanning electron microscope on the surface of the diffractive microlens. Surface roughness data tested shows that the surface roughness of fabricated diffractive microlens is in the nanometer range, which has reached the level of optical mirror. The optical aperture is in the micrometer range. The characteristics of the micro-structures on the surface and the optical aperture can be set and arranged flexibly by the iterative angular spectrum algorithm, according to the characteristics and parameters of the incident and outgoing beam. The results of optical characteristics measurement show that the diffractive microlens can focus incident red laser into a very small bright focal spot, and the phenomenon of focusing and defocusing is obvious. The analysis of beam quality shows that the intensity distribution and size of the focal-spot is in accord with pre-calculated results. The fabricated diffractive microlens indicates a very high diffraction efficiency. The experimental results demonstrate that the performances of the diffractive microlens can be further improved by modifying the design algorithm and optimizing the manufacture craft.