Philippe Nussbaum

Design, fabrication and testing of microlens arrays for sensors and microsystems

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 (, blood gas sensor), neural networks and multiple pupil imaging systems for photolithography (microlens and smart mask lithography) are presented.

Microlens array imaging system for photolithography

Keywords: flat panel displays ; compound eye ; microlenses ; micro-optics ; multi-aperture imaging ; optical images ; photolithography ; photoresists Reference EPFL-ARTICLE-183166 Record created on 2013-01-17, modified on 2017-05-10

Simple technique for replication of micro-optical elements

A simple technique for the replication of micro-optical elements is presented. Elastomeric material is used to realize a negative mold of the original optical element and UV-curing adhesive is used to make the replicated copy. Replicated elements, such as refractive and diffractive micro-optical elements, are produced. The refractive microlenses have a diameter of 970 µm and a height of 79 µm and the diffractive element is a multilevel blazed grating with a period of 64 µm. The characteristics of the replicated elements are measured using different methods. The deviation from a sphere of the original and the replicated refractive microlenses is 0.13?. and 0.12?. root mean square (rms), respectively. The replicated multilevel blazed grating has a diffraction efficiency of over 80%. An alternative method for realizing planoconcave microlenses from a planoconvex master is also presented.

Low numerical aperture refractive microlenses in fused silica

Fused silica microlenses with low numerical apertures (NAs) were fabricated. The original photoresist element was realized by the melting resist technology and was transferred into fused silica by reactive ion etching. Low selectivity etching was applied to realize the low NA microlenses. An etch selectivity between photoresist and fused silica down to 0.1 was achieved by using SF6 and O2 gases. Refractive microlenses with NAs down to 0.018 were obtained.

Microlens lithography: a new approach for large display fabrication

Microlens lithography is a new lithographic method, that uses microlens arrays to image a lithographic mask onto a substrate layer. Microlens lithography provides photolithography at a moderate resolution for an almost unlimited area. The imaging system consists of stacked microlens arrays forming an array of micro-objectives. Each micro-objective images a small part of the mask pattern, the images overlap in the image plane. Potential applications for microlens lithography are the fabrication of large area flat panel displays (FPD), color filters, and micromechanics.

Design, fabrication, and testing of micro-optical components for sensors and microsystems

We report on our activities in the design, fabrication, characterization and system integration of planar micro- optical elements. Microlens arrays, gratings, diffusers, beam shapers and beam splitters have been fabricated, tested and integrated in chemical analysis systems ((mu) TAS, fluorescence detection), tracking sensors for satellites, displacement sensors, optical lightpipes, LCD projector illumination photospectrometers, neural networks and multiple channel imaging systems for photolithography. Packaging and alignment strategies for sensors and optical microsystems were investigated.

MICRO- OPTICS FOR SENSOR APPLICATIONS

Our investigation is focused on microlens arrays for microsystems and sensor applications. Arrays of refractive lenses (2 micrometer to 5 mm lens diameter) have been fabricated by melting resist technology. Microlens arrays have been transferred in fused silica (reactive ion etching) and replicated in polycarbonate and polymer (embossing, casting). Lens arrays have been integrated into lithographic systems, sensors and neural networks.

Fabrication technologies for micro-optical elements with arbitrary surfaces

We present a comparison of three different technologies for the fabrication of micro-optical elements with arbitrary surfaces. We used direct laser writing in photoresist, binary mask lithography in combination with reactive ion etching in fused silica, and High-Energy- Beam-Sensitive (HEBS) glass graytone lithography in photoresist. We analyzed the efficiencies and the deflection angles of different elements in order to quantify the performance of the different technologies. We found that higher effencies can be achieved with refractive type elements, while precise deflection angles can be obtained more easily with diffractive elements.

Miniaturized, focusing fan-out elements: design, fabrication and characterization

We present miniaturized, focusing fan-out elements. The new micro-optical elements were fabricated using different technologies: double-sided injection moulding in polycarbonate, double-sided photolithography with subsequent transfer in quartz and direct laser writing in photoresist. The fan-out elements were characterized by measuring their efficiency and uniformity, the surface profiles of the microlenses were measured with a Twyman-Green interferometer. The overall performance of the combined, hybrid elements is demonstrated with intensity distributions recorded in the focal planes.

Refractive and diffractive elements for micro-optical systems

We report on our activities in the design, fabrication and characterization of refractive and diffractive micro-optical elements and their integration into micro-systems. Various fabrication techniques like interferometric recording, mask projection steps, or direct writing are used to generate high resolution surface-relief profiles in photoresist. The transfer of the surface profile into glass or quartz is possible using reactive ion etching (RIE). Low-cost micro- optical elements can be fabricated in organic polymers using various replication techniques. Different types of micro- optical elements can be integrated on a substrate together with other opto-electronic components. We present selected applications in the field of laser beam shaping, space communications and blood gas sensors.