Miniaturized achromatic hybrid objective containing LIGA-made microlenses

The design, realization and characterization of a miniaturized objective are presented. The goal was to obtain an objective with a wide angular field in water, dedicated to noninvasive surgery. This demonstrator proves the usefulness of polymer microlenses (obtained by hot embossing) and outlines the critical steps of the manufacturing process. The objective is 4 mm long, has a diameter of 0.9 mm and an angular object field of 90 degrees (in water). It consists of one pair of concave glass microlenses and two polymethyl methacrylate (PMMA)/glass doublets. The starting design data were imposed by both the previously obtained PMMA microlens characteristics and by the application itself. The small-size-adapted classical technological flux used to manufacture the glass microlens is described and compared to the specific LIGA technological flux used to obtain the PMMA microlenses. Qualitative and quantitative functional characterizations of the components and of the obtained miniaturized optical system (e.g. object field, distortion, MTF, etc.) are performed and discussed. The problems encountered during manufacturing, assembling and characterization processes are outlined and their influence upon the functional characteristics is revealed.