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Recent developments in wafer-level fabrication of micro-optical multi-aperture imaging systems

: Leitel, R.; Dannberg, P.; Brückner, A.; Bräuer, A.


Mazuray, L. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Optical Design and Engineering IV : 5.-8.9.2011, Marseille, France; SPIE Optical System Design 2011
Bellingham, WA: SPIE, 2011 (Proceedings of SPIE 8167)
ISBN: 978-0-8194-8793-3
Paper 81670P
Conference "Optical Design and Engineering" <2011, Marseille>
Conference Paper
Fraunhofer IOF ()
micro-optics; imaging system; compound eye; camera; multi aperture

Micro-optical systems, that utilize multiple channels for imaging instead of a single one, are frequently discussed for ultra-compact applications such as digital cameras. The strategy of their fabrication differs due to different concepts of image formation. Illustrated by recently implemented systems for multi-aperture imaging, typical steps of wafer-level fabrication are discussed in detail. In turn, the made progress may allow for additional degrees of freedom in optical design. Pressing ahead with very short overall lengths and multiple diaphragm array layers, results in the use of extremely thin glass substrates down to 100 microns in thickness. The desire for a wide field of view for imaging has led to chirped arrays of microlenses and diaphragms. Focusing on imaging quality, aberrations were corrected by introducing toroidal lenslets and elliptical apertures. Such lenslets had been generated by thermal reflow of lithographic patterned photoresist and subsequent molding. Where useful, the system's performance can be further increased by applying aspheric microlenses from reactive ion etching (RIE) transfer or by achromatic doublets from superimposing two moldings with different polymers. Multiple diaphragm arrays prevent channel crosstalk. But using simple metal layers may lead to multiple reflections and an increased appearance of ghost images. A way out are low reflecting black matrix polymers that can be directly patterned by lithography. But in case of environmental stability and high resolution, organic coatings should be replaced by patterned metal coatings that exhibit matched antireflective layers like the prominent black chromium. The mentioned components give an insight into the fabrication process of multi-aperture imaging systems. Finally, the competence in each step decides on the overall image quality.