Microoptical artificial compound eyes

Two different artificial compound eye concepts for compact vision systems have been investigated in detail: The artificial apposition compound eye objective and the cluster eye. Optical design methods and characterization tools were developed or modified to allow the layout and analysis of the microoptical imaging systems which were fabricated for the first time by microoptics technology

Overview of microoptics: Past, present, and future

Through advances in semiconductor miniaturization technology, microrelief patterns, with characteristic dimensions as small as the wavelength of light, can now be mass reproduced to form high-quality and low-cost optical components. In a unique example of technology transfer, from electronics to optics, this capability is allowing optics designers to create innovative optical components that promise to solve key problems in optical sensors, optical communication channels, and optical processors

Novel end-fly-cutting-servo system for deterministic generation of hierarchical micro–nanostructures

This paper reports on the diamond cutting based generation of hierarchical micro-nanostructures, which are conventionally difficult for both mechanical and non-mechanical methods to achieve. A novel end-fly-cutting-servo (EFCS) system, with four-axis servo motions that combine the concepts of fast/slow tool servo and endface fly-cutting, is proposed and investigated. In the EFCS system, an intricately shaped primary surface is generated by material removal, while the desired secondary nanostructures are simultaneously constructed using residual tool marks by actively controlling tool loci. The potential of the EFCS system is demonstrated firstly by fabricating a nanostructured F-theta freeform surface and a nanostructured micro-aspheric array

Compact infrared cryogenic wafer-level camera: design and experimental validation

International audienceWe present a compact infrared cryogenic multichannel camera with a wide field of view equal to 120 degrees. By merging the optics with the detector, the concept is compatible with both cryogenic constraints and wafer-level fabrication. The design strategy of such a camera is described, as well as its fabrication and integration process. Its characterization has been carried out in terms of the modulation transfer function and the noise equivalent temperature difference (NETD). The optical system is limited by the diffraction. By cooling the optics, we achieve a very low NETD equal to 15 mK compared with traditional infrared cameras. A postprocessing algorithm that aims at reconstructing a well-sampled image from the set of undersampled raw subimages produced by the camera is proposed and validated on experimental images. (C) 2012 Optical Society of Americ

Chirped refractive microlens arrays

The presented thesis deals with the design, the fabrication, and the characterization of nonregular microlens arrays that are referred to as "chirped microlens array" (cMLA) in accordance to other non-periodical structures. In contrast to conventional, regular microlens arrays that consist of a repetitive arrangement of a unit cell on a fixed, equidistantly sectioned grid, a cMLA contains similar but not identical lenses that are defined by a parametric description. The parameters of each cell can be defined by analytical functions, by using numerical optimization techniques, or by a combination of the both. Dependency on the position of the cell within the array is the most characteristic property of these functions. Overcoming the inflexibility of a regular arrangement leads to the enhancement of the classical array concept and enables new degrees of freedom in the design of micro-optical systems. The focus of this thesis is to point out the potentials of these new design possibilities which are explained by example systems built as prototypes. Fields of application are amongst others the improvement of the system's integration and the optimization of the optical performance of a system. Applications in the field of beam shaping and miniaturized imaging optics are discussed in detail as example systems. The latter enables extremely thin imaging objectives with a track length shorter than 250µm that have their natural antetype in the compound eyes of insects. The use of a cMLA allows the correction of off-axis aberrations and consequently the extension of the field of view of the objective, whereas the array describing function can be derived analytically. For the rst time, the use of a cMLA with individually adapted lenses allows the fabrication of objectives based on the well-known imaging principle that are compliant to the demands of industrial applications rather than just being proof-of-principle demonstrators. Furthermore, a fly's eye condenser setup based on cMLAs is discussed. In contrast to the application examples mentioned before, here the focus is on the collective interaction of all lenses of the array that leads to novel coherent effects. The periodic intensity peaks appearing in the plane of homogenization which are typical when using regular arrays can be avoided by employing non-periodic arrays. This leads to an improved homogeneity of the radiation. Fly's eye condensers based on cMLAs are especially advantageous when dealing with short pulse applications such as in sensing or material processing since otherwise applicable homogeneity improving measures are not suitable. The microlens arrays are fabricated using reflow of photoresist or laser lithography which had to be adapted to the specifics of cMLAs. This concerns especially software tools for the generation of mask layouts for the reflow of photoresist as well as profile data for laser lithography which had to be developed beforehand the prototyping and are now available as universal tools.Die vorliegende Arbeit befasst sich mit Aspekten des Designs, der Herstellung und der Charakterisierung nichtregulärer Mikrolinsenarrays, für die in Anlehnung an weitere nichtperiodische Strukturen der englischsprachige Begriff "chirped microlens array" (cMLA) eingeführt wurde. Im Gegensatz zu klassischen - regulären - Mikrolinsenarrays, die aus identischen Linsen mit konstantem Abstand zueinander gebildet werden, bestehen cMLAs aus ähnlichen, jedoch nicht identischen Linsen, die mittels parametrischer Beschreibung deniert sind. Die Zelldefinition kann durch analytische Funktionen, numerische Optimierungsverfahren oder eine Kombination aus beiden gewonnen werden. Bei allen gechirpten Arrays hängen die Funktionen von der Position der jeweiligen Zelle im Array ab.insen mit konstantem Abstand zueinander gebildet werden, bestehen cMLAs aus ähnlichen, jedoch nicht identischen Linsen, die mittels parametrischer Beschreibung deniert sind. Die Zelldefinition kann durch analytische Funktionen, numerische Optimierungsverfahren oder eine Kombination aus beiden gewonnen werden. Bei allen gechirpten Arrays hängen die Funktionen von der Position der jeweiligen Zelle im Array ab. Die Loslösung von der starren Geometrie regulärer Arrays führt zu einer Erweiterung des klassischen Arraybegriffes und ermöglicht neue Freiheitsgrade im Design mikrooptischer Systeme. Der Schwerpunkt der Arbeit ist auf das Aufzeigen der neuen Designmöglichkeiten gerichtet, welche anhand von prototypenhaft umgesetzten Beispielsystemen erläutert werden. Anwendungsgebiete sind hierbei unter anderem die Verbesserung der Integrationsmöglichkeiten und die Optimierung der Funktionsparameter optischer Systeme. Exemplarisch werden hierzu optische Designs und Prototypen diskutiert, die unter anderem Anwendungen in der Strahlformung und der miniaturisierten Abbildungsoptik besitzen. Letzteres betrifft ein ultra-dünnes Kamerasystem, welches auf einem Sehprinzip von Insekten basiert und Baulängen kleiner als 250um ermöglicht. Hierbei findet ein cMLA Einsatz, welches die Korrektur außeraxialer Bildfehler und damit die Vergrößerung des Gesichtsfeldes der Kamera ermöglicht. Die das Array beschreibenden Funktionen können hierbei vollständig analytisch abgeleitet werden. Die Nutzung eines cMLA aus individuell angepassten Linsen ermöglicht damit erstmals, das bekannte Abbildungsprinzip von akademischen Prinzipprototypen zu Systemen mit optischen Parametern zu erweitern, die den Einsatzbedingungen industrieller Anwendungen genügen. Weiterhin wird ein Wabenkondensoraufbau auf Basis von cMLAs zur Strahlhomogenisierung behandelt. Im Gegensatz zu den zuvor aufgeführten Anwendungsbereichen von cMLAs steht hierbei die Interaktion der Gesamtheit aller Linsen des Arrays im Mittelpunkt, was im Besonderen zu neuartigen kohärenten Effekten führt. Die Nutzung nichtregulärer Arrays ermöglicht die Vermeidung der ansonsten auftretenden periodischen Intensitätsmaxima und -minima in der Homogenisierungsebene, was mit einer Verbesserung der Homogenität einhergeht. Wabenkondensoren auf Basis von cMLAs sind im Speziellen für Kurzpulsanwendungen in der Sensorik und Materialbearbeitung von Interesse, da andere homogenitätsverbessernde Maßnahmen nicht angewendet werden können. Für die Herstellung der Arraystrukturen werden das Reflow von Fotolack und die Laserlithographie genutzt, die an die Besonderheiten der cMLAs anzupassen waren. Dies betrifft im Speziellen Softwaretools zur Erstellung von Maskendaten für den Reflowprozess und von profilbeschreibenden Daten für die Laserlithographie, die im Vorfeld der Prototypenfertigung entwickelt wurden und als universelle Werkzeuge zur Verfügung stehen

Fabrication of microlens arrays with varied focal lengths on curved surfaces using an electrostatic deformed template

A microlens array (MLA) with varied focal length was fabricated on a curved surface for the application of compound-eye imaging. Electrostatic deformed concave membrane was used as the initial molding template, and the deformation was determined by different applied voltage. By transferring the pattern to another polymeric template and deforming it by negative pressure, MLAs on a curved surface were fabricated successfully by using this molding process and polymeric template. The fabricated MLAs were optically characterized and the result demonstrated a larger field-of-view than that of flat MLAs and better imaging performance than that of MLAs with uniform focal length on curved surfaces. ? 2014 IOP Publishing Ltd

Field curvature correction in multichannel miniature imaging systems suited for wafer-level production

Using multiple optical channels increases the number of design possibilities for the objectives of mobile imaging devices. For easy waferlevel fabrication, we start from a single optical element—a monocentric plano-convex lens. The quality of the areal image is used to select the size of the field of each channel. Each channel optics is axially positioned to reduce the effect of the image field curvature. The resulting device has a small number of channels and it images a full field of view of ±40 deg with an f -number of 3. Details of the optical design, of the fabrication process, and of the device performance are reported

Micro-embossing of micro-structures in RSA-501 as mold inserts for the replication of micro-lens arrays

The production of mold inserts for the replication of micro-lens arrays through micro-embossing could be an alternative process route compared to diamond turning or milling in order to reduce time and costs. The rapidly solidified aluminum alloy RSA-501 is expected to form micro-structures with low surface roughness because of its ultra-fine grain structure. In micro-embossing challenges like elastic spring back effect, pile-ups, and forming accuracy depend on the material behavior. Therefore, RSA-501 was further characterized and the influence of polishing or flycutting on the material behavior was investigated. To further understand the grain and microstructure samples were sectioned along their cross and longitudinal directions. The grain structure of RSA-501 was oriented along the extrusion direction and the mean grain sizes were <1.00 μm. Furthermore, RSA-501 was micro-embossed to investigate the influence of the material behavior and surface preparation on the forming of micro-structures. The induced surface integrity through flycutting was not deep enough to influence the forming of micro-structures. Therefore, the workpiece surface can be prepared either by polishing or flycutting. When micro-embossing RSA-501, cross and longitudinal sections can be used. However, it is recommended to process the cross section because of its isotropic grain structure. It was shown that the curvature radius of micro-embossed concave structures differs from the tool radius. This is due to the elastic spring back effect. Since the embossed structure remains spherical, the spring back effect can be compensated by adjusting the tool radius