Abstract.We report on our activities in design, fabrication, characterization and system integration of refractive microlens arrays for sensors and microsystems. Examples for chemical analysis systems (µTAS, blood gas sensor), neural networks and multiple pupil imaging systems for photolithography (microlens and smart mask lithography) are presented.

We review the most important fabrication techniques for glass and plastic refractive microlenses and we quantitatively characterize in a systematic way the corresponding state-of-the-art microlenses, which we obtained from selected research groups. For all our measurements we rely on three optical instruments: a non-contact optical profiler, a transmission Mach-Zehnder interferometer and a Twyman-Green interferometer. To conclude, we survey and discuss the different fabrication techniques by comparing the geometrical and optical characteristics of the microlenses, the range of materials in which the lenses can be produced, their potential for low-cost fabrication through mass-replication techniques and their suitability for monolithic integration with other micro-optical components.

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A new optical concept for compact digital image acquisition devices with large field of view is developed and proofed experimentally. Archetypes for the imaging system are compound eyes of small insects and the Gabor-Superlens. A paraxial 3x3 matrix formalism is used to describe the telescope arrangement of three microlens arrays with different pitch to find first order parameters of the imaging system. A 2mm thin imaging system with 21x3 channels, 70 masculinex10 masculine field of view and 4.5mm x 0.5mm image size is optimized and analyzed using sequential and non-sequential raytracing and fabricated by microoptics technology. Anamorphic lenses, where the parameters are a function of the considered optical channel, are used to achieve a homogeneous optical performance over the whole field of view. Captured images are presented and compared to simulation results.

This article presents a new integrated microfluidic/microoptic device designed for basic biochemical analysis. The microfluidic network is wet-etched in a Borofloat 33 (Pyrex) glass wafer and sealed by means of a second wafer. Unlike other similar microfluidic systems, elements of the detection system are realized with the help of microfabrication techniques and directly deposited on both sides of the microchemical chip. The detection system is composed of the combination of refractive circular or elliptical microlens arrays and chromium aperture arrays. The microfluidic channels are 60 µm wide and 25 µm deep. The elliptical microlenses have a major axis of 400 µm and a minor axis of 350 µm. The circular microlens diameters range from 280 µm to 350 µm. The apertures deposited on the outer chip surfaces are etched in a 3000-Å-thick chromium layer. The overall thickness of this microchemical system is <1.6 mm. A limit of detection of 3.3 nM for a Cy5 solution in phosphate buffer (pH 7.4) was demonstrated. The crosstalk signal measured between two adjacent microchannels with 1 mm pitch was <1:5600, meaning that e1.8 × 10 -4 % of the fluorescence light power emitted from one microchannel filled with a 50 µM Cy5 solution reaches the photodetector at the adjacent microchannel. This performance compares very well with that obtainable in microchemical chips using confocal fluorescence systems, taking differences in parameters, such as excitation power into microchannels, data acquisition rates, and signal filtering into account.

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Abstract:The optical properties of plano-convex refractive microlenses with low Fresnel Number (typically FN < 10) are investigated. It turns out that diffraction effects at the lens aperture limit the range of the effective focal length. The upper limit of the focal length is determined by the diffraction pattern of a pinhole with equal diameter. In addition achromatic microlenses can be realized because refraction and diffraction have opposing effects on the focal length. Gaussian beam propagation method has been used for simulation. The presented results are of relevance for applications, where microlenses with small apertures and long focal lengths are used, for example, Shack Hartmann wavefront sensors or confocal microscopes. References

Abstract. Micro-optical systems based on refractive microlenses are investigated. These systems are integrated on a chemical chip. They focus an excitation beam into the detection volume (microliter or even submicroliter scale) and collect the emitted light from fluorescent molecules. The fluorescence must be carefully separated by spatial and spectral filtering from the excitation. This paper presents the ray tracing simulation, fabrication, and measurement of three illumination systems. The measurements show that an adroit placement and combination of microfabricated lenses and stops can increase the separation between the excitation light and the fluorescence light. Moreover we present the successful detection of a 20 nM Cy5™ (Amersham Life Science Ltd.) solution in a 100-m-wide and 50-m-deep microchannel (excitation volume Ϸ250 pL) using one of these illumination systems. The microchemical chip with the micro-optical system has a thickness of less than 2 mm.