The recently introduced ROLICURETM PEARL is a novel optically variable device (OVD) ideally suited for security applications. It may hold high resolution images, (micro-) text or graphical designs. Upon tilt or rotation high contrast positive/negative flips are observed. The optical effect of these devices is based on a proprietary technology of Rolic and includes light scattering at patterned anisotropic microstructures. Since these microstructures are non-periodic no rainbow colors are generated, making these devices easy to authenticate and clearly distinguishable from standard holograms. In this paper, we describe how to modify the optical appearance of our - a priori - colorless ROLICURETM PEARL feature by addition of distinct color-shift thus further increasing its level of protection and meeting design requirements. This is accomplished by optical interference at additional dielectric and metallic layers in combination with the ROLICURETM PEARL scattering microstructure. Various configurations are conceivable and have been realised in our labs. Depending on the nature of its dielectric layers red, green and blue colors are obtained and respective photospectra will be presented. While the optical appearance remains attractively bright, excellent color saturation is achievable. Independently from the color-shift which originates from changes of the optical path length under various viewing angles, the contrast inversion of the image is still present and is visualized when the device is tilted or rotated. In general, images of these security devices are easily recognizable within wide viewing angles without need of a point light source.
The vast majority of liquid crystal (LC) devices are used today in displays and image projection systems. The goal of this work is to demonstrate that with LC other helpful optical components can also be built. Two classes of devices are presented. The first class represent 1-dimensional spatial light modulators with high resolution electrodes to be used as beam steering devices. These devices are parallel LC cells and represent electrically controllable birefringent phase gratings. The second class involves what we call polarization converter devices and which represent the passive LC devices. These nematic LC devices are fairly easy to fabricate and a new class of light fields can be generated with them, namely linearly polarized light with axial symmetry. These fields are very difficult to generate unless the LC components described here are used.
The realization of an integrated, flexible, and robust CIM vision system, suitable for performing quality-assurance surface inspections is discussed. The optimized combination of advanced optics, optomechanics, and flexible image sensor realizes a high 'virtual resolution' without penalizing the pixel transfer rate. High computation rates are obtained by complementing the fractal inspection algorithm with a dynamic hologram, a modular data flow processor, and the system computer. The integrated vision system is validated for the surface quality inspection of concrete tiles in an industrial environment. The overall system performance is discussed in detail and the potential of the system for other application fields will be addressed.
A novel active vision system for CIM production and inspection applications has been developed in the framework of ESPRIT II project No. 5194 (CIVIS). The system consists of a unique, integrated combination of novel components: camera head, data acquisition electronics, a custom digital image processor, control hardware and a commercial framestore, all under the direction of control and processing software on a PC-486 platform. The camera head incorporates a fast zoom lens in combination with a pan/tilt mirror system, allowing region-of-interest acquisition. The special 256 X 256 MOS image sensor offers programmable resolution and random pixel access. The unique combination of optics, optomechanics and versatile image sensor has a high `virtual resolution,' corresponding to more than 1k X 1k pixels but without the overhead of a high pixel transfer rate. The fast computation of the algorithm employed for the fractal inspection of surfaces is realized with an unusual combination of an electrically switchable hologram (for performing all linear operations at the speed of light in the optical domain), a module-based digital processor and the host computer. In this way, active vision for the inspection of concrete tile surfaces has been implemented by acquiring only relevant image data and elegantly processing them in the most appropriate domain.
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