Multi-aperture Approach Research Articles

Multi-aperture optics for wafer-level cameras

Wafer-level optics is considered to yield imaging lenses for cameras of the smallest possible form factor. The high accuracy of the applied microsystem technologies and the parallel fabrication of thousands of modules on the wafer level make it a hot topic for high-volume applications with respect to quality and costs. However, the adaption of existing materials and technologies from microoptics for the manufacturing of millimeter scale lens diameters led to yield problems due to material shrinkage and z-height accuracy. A multi-aperture approach to real-time vision systems is proposed that overcomes these issues because it relies on microlens arrays. The demonstrated prototype achieves VGA (Video Graphics Array, 640×480 pixels) resolution with a thickness of 1.4 mm, which is a thickness reduction of 50% compared to single-aperture equivalents. The partial images that are separately recorded in different channels are stitched together to form a final image of the whole field of view by means of image processing. Distortion is corrected within the processing chain. The microlens arrays are realized by state-of-the-art micro-optical fabrication techniques on wafer level that are suitable for a potential application in high volume, e.g., for consumer electronic products.

Developing high brightness and high current beams for HIF injectors

The U.S. Heavy Ion Fusion Virtual National Laboratory is continuing research into ion sources and injectors that simultaneously provide high current (0.5–1.0 A) and high brightness (normalized emittance better than 1.0 π-mm-mr). The central issue of focus is whether to continue pursuing the traditional approach of large surface ionization sources or to adopt a multiaperture approach that transports many smaller “beamlets” separately at low energies before allowing them to merge. For the large surface source concept, the recent commissioning of the 2-MeV injector for the High Current eXperiment has increased our understanding of the beam quality limitations for these sources. We have also improved our techniques for fabricating large diameter aluminosilicate sources to improve lifetime and emission uniformity. For the multiaperture approach, we are continuing to study the feasibility of small surface sources and a RF-induced plasma source in preparation for beamlet merging experiments, while continuing to run computer simulations for better understanding of this alternate concept. Experiments into both architectures will be performed on a newly commissioned ion source test stand at Lawrence Livermore National Laboratory called STS-500. This stand test provides a platform for testing a variety of ion sources and accelerating structures with 500-kV, 17-μs pulses. Recent progress in these areas is discussed as well as plans for future experiments.

Features for detecting obscured objects in ultra-wideband (UWB) SAR imagery using a phenomenological approach

We describe a technique that is based on phenomenological principles for detecting man-made objects in ultra-wideband (UWB) synthetic aperture radar (SAR) imagery. The UWB sensor (50 MHz to a GHz) provides penetration and high resolution necessary for detecting man-made objects that are obscured by some random media. Traditional 2-D pattern matching techniques are not effective since the SAR image of an object is distorted by the obscuring media. An electromagnetic model is used to predict the backscatter received from the scene objects. We show that the backscatter is highly dependent on the aspect angle of the incident wave on the object. Man-made objects exhibit specular reflections, at certain aspect angles while natural objects generally do not. Aspect-angle signatures of objects are established using a multi-aperture approach which essentially reconstructs the SAR image of an object over smaller subapertures of the full synthetic aperture. These signatures are matched to the object's polarimetric counterparts to establish feature vectors, which are used for detection. This procedure is applied to detection of man-made vehicles that are embedded in a deciduous forest and obscured by foliage. Results are presented using real data.