Refractive and diffractive micro-optical elements and arrays prepared by the fast sol-gel processes

The optical quality of films and bulk elements obtained by the fast sol-gel method and the ease of preparation make this method technologically and economically attractive for micro- optical elements and arrays. Multiple replication of high-cost metal templates necessitates a two step process: initial replication onto disposable plastic, to produce negative- templates, and casting of the glass elements onto these plastic templates. Following introduction of the fast sol-gel micro-replication processes, the fabrication of refractive and diffractive micro-optical arrays is described in detail. The study focuses of the accuracy achievable by the replication of sharp curvatures by a viscous sol-gel resins. A further question addressed is how to obtain a thick crack-free self- supporting micro-optical array by such a process. Examples of replication results of Fresnel lenses and various types of lenslet arrays by this method are shown, and the various aspects of replication accuracy are discussed. The characterization of the thus produced micro-optical arrays is described, relating to the influence of mold and resin parameters on residual stresses and thence, the surface and bulk properties of the replicas. Various approaches to stress- minimization that can facilitate accurate replication in sol- gel derived matrices are discussed. Further, the preparative approach to highly patterned crack-free self-supporting thick elements is displayed, and the wide scope of new applications stemming from such elements is discussed. Finally, the new chemical approach to crack-free stress-free silica glasses by the sol-gel method is displayed.