A Concept for Zero-Alignment Micro Optical Systems Page: 1 of 9
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A Concept for Zero-Alignment Micro Optical Systems
Raviv Levy and Michael R. Descourt
Optical Sciences Center, University of Arizona, Tucson, Arizona 85721 a o
Randy J. Shul, Christi L. Willison, and Mial E. Warren __
Sandia National Laboratories, Albuquerque, New Mexico 87185 I
Terho Kololuoma and Juha T. Rantala
VTT Electronics, 90571 Oulu, Finland
ABSTRACT
We are developing a method of constructing compact, three-dimensional photonics systems consisting of
optical elements, e.g., lenses and mirrors, photo-detectors, and light sources, e.g., VCSELs or circular-grating lasers.
These optical components, both active and passive, are mounted on a lithographically prepared silicon substrate.
We refer to the substrate as a micro-optical table (MOT) in analogy with the macroscopic version routinely used in
optics laboratories. The MOT is a zero-alignment, microscopic optical-system concept. The position of each optical
element relative to other optical elements on the MOT is determined in the layout of the MOT photomask. Each
optical element fits into a slot etched in the silicon MOT. The slots are etched using a high-aspect-ratio silicon
etching (HARSE) process. Additional positioning features in each slot's cross-section and complementary features
on each optical element permit accurate placement of that element's aperture relative to the MOT substrate.
In this paper we present the results of the first fabrication and micro-assembly experiments of a silicon-
wafer based MOT. Based on these experiments, estimates of position accuracy are reported. We also report on
progress in fabrication of lens elements in a hybrid sol-gel material (HSGM). Diffractive optical elements have
been patterned in a 13-micron thick HSGM layer on a 150-micron thick soda-lime glass substrate. The measured
rns surface roughess was 20 nm. Finally, we describe modeling of MOT systems using non-sequential ray tracing
(NSRT).
Keywords: micro-optical systems, hybrid sol-gel material, systems with diffractive optics
1. INTRODUCTION
An optical table allows the two-dimensional assembly of optical elements of different functionality. We
are proposing to miniaturize the optical table and to develop fabrication and micro-assembly techniques that
preserve the versatility of an optical table while at the same time allowing for highly accurate, passive alignment of
a wide variety of passive and active optical elements. The result is the micro-optical table (MOT) concept and the
associated idea of a photonics cube.
Extensive work in the development of micro-optical systems has been performed by Wu, et al.' That
research is based on the fabrication of optical elements on micro-hinges using surface micro-machining techniques.
The optical elements are raised from the prone position to form an optical bench. Tilt of the elements is controlled
by the use side latches. An attractive feature of the free-space micro-optical bench (FS-MOB) technology is the
capability to integrate micropositioners. and microactuators into the optical bench using the same surface-
micromachining techniques as those used to fabricate the optical elements. A difference between the FS-MOB
technology and the MOT/photonics-cube approach has to do with the type of micromachining that is employed in
each case. FS/MOB systems are fabricated using surface micromachining whereas MOT/photonics-cube systems
are fabricated using bulk micromachining of a substrate material such as silicon. The required silicon bulk-
micromachining processes are a recent development.2
Optical benches have also been fabricated using the LIGA process.t One example has been reported by
Muller, et al.3 This LIGA bench contains two ball lenses and a spectral filter. The micro-optical LIGA bench
allows passive alignment of two 900-gm-diameter ball lenses, a filter plate, and an optical fiber. The mounting slot
for the filter plate is rectangular in cross-section. The mounting slot in this LIGA bench does not include any
optomechanical features to tighten the alignment of optical elements.
t E-mail address: michael.descour@optics.arizona.edu; Web site address: http://www.optics.arizona.edu/Descour/lensl.htm.
* LIGA (Lithographie, Galvanoformung und Abformung).
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DESCOUR, MICHAEL R.; KOLOLUOMA,TERHO; LEVEY,RAVIV; RANTALA,JUHA T.; SHUL,RANDY J.; WARREN,MIAL E. et al. A Concept for Zero-Alignment Micro Optical Systems, article, September 16, 1999; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc624015/m1/1/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.