<title>Compact self-aligning assemblies with refractive microlens arrays made by contactless embossing</title>

Abstract

The hybrid integration of microlenses and arrays of microlenses in micro-optical systems is simplified using contactless embossing of microlenses (CEM) in combination with LIGA microfabrication. CEM is a new fabrication technique for the production of precise refractive microlens arrays. A high precision matrix of holes made by LIGA technique is used as a compression molding tool to form the microlenses. The tool is pressed onto a thermoplastic sample which is heated close to the glass transformation temperature of the material. The material bulges into the openings of the molding tool due to the applied pressure and forms lens-like spherical structures. The name refers to the fact that the surface of the microlens does not get in contact with the compression molding tool during the shaping process and optical quality of the surface is maintained. Microlenses and arrays of microlenses with lens diameters from 30 μm up to 700 μm and numerical aperture values of up to 0.25 have been fabricated in different materials (e.g. thermoplastics like PMMA, PC etc.). Cost-effectiveness in the production process, excellent optical performance and the feature of easy replication are the main advantages of this technique. The most promissing feature of this method is the possibiliy to obtain self-aligned assemblies consisting of a temperature-resistant part which acts as a compression molding tool for the lens shaping and the CEM microlens arrays. Containing additional precise alignment structures these assemblies then can be further integrated into a micro-optical bench setup. The CEM fabrication method in combination with LIGA microfabrication considerably enhances the hybrid integration in micro-optical devices which results in a more cost-effective production of compact micro-opto-electro-mechanical systems (MOEMS).