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The deflection of the scanning grating device used in this kind of MEMS based spectrometers becomes a limiting factor for extending the spectral range. By using a plain scanner mirror which illuminates a fixed grating and gathers the reflected radiance simultaneously the spectral range can be doubled applying the same MEMS deflection.
Furthermore, the wider spectral range can be supported by using two or more detectors with different spectral characteristics placed behind two or more separated exit slits. These slits could be integrated into the same MEMS chip like the scanner mirror device.
Several optical designs for miniaturized setups have been compared to find an optimized option which requires affordable optical components only. Here especially the two mirrors in the setup are relevant for a suitable spectrometer performance with acceptable effort. Finally a folded Czerny-Turner type setup has been chosen which can be integrated by the “place and bend” assembly.
A new concept for the efficient realization of complex optical systems has been invented and patented [1]. For the so-called "place and bend assembly" a planar substrate is used which features preprocessed bending lines. Due to the progress in production technologies, 3D printing for small and medium volumes as well as other advanced plastic process technologies for high volumes with supreme accuracy are available. Optical, electronic as well as MEMS components can be placed on such a substrate using standard but precise planar technologies. Then the different parts of the substrate are bent and form the 3D body. Simultaneously the optical path inside is generated. This concept is not limited to rectangular shapes. It may also be possible to realize the "W-configuration" of a Czerny-Turner spectrometer in a very efficient way.
The first proof of concept has been achieved with a camera device realized from a 3D printed substrate. An entrance window, two spherical mirrors, an aperture stop and a detector array have been assembled using planar technology. Afterwards the substrate was folded and fixed. The functional capability has been demonstrated by capturing test images which have been optically evaluated. Challenges for the future development will be named and discussed.
Resonant MEMS devices combine multiple advantages: Ultra compact designs can be realized, MEMS motions allow an operation using a single detector to meet cost issues even with extended InGaAs technology and the position feedback ensures a precise and long term stable wavelength scale. Based on such resonantly actuated MEMS components NIR spectrometers have been designed. Recent research work aims for extreme miniaturization of the optical bench. The presented assembly technology has been optimized for volume production. The outline from the previous published work will be shrunk to 10 x 10 x 5 mm3 with only a slightly reduced resolution. The new design will be optimized for cost efficient production as well.
Up to now volume production of photonic systems has been optimized for on-axis lens based optical systems. Chromatic aberration limits the usage or spectral range of these systems. Applying mirrors instead of lenses may help to suppress chromatic aberrations and wavelength depending absorption. The assembly of reflective optics, often in an off-axis configuration, is a complex process. So far most tools for volume production apply stacking of components in planar technology. Off-axis systems are typically assembled by more or less manually alignment of the components, which is not in favor for mass and low cost production of these systems.
The novel approach utilizers a planar substrate featuring preprocessed bending lines. A high accuracy tool for planar assembly places the components onto the substrate. Then the sides of the substrate are bent leading to a predefined three dimensional body. The off-axis optical path inside is generated automatically.
This concept is not limited to rectangular shapes but can also be applied to more complex systems, for example the so called “W-configuration” for a Czerny-Turner spectrometer.
First tests of the “bend and place assembly” have been performed successfully on a camera setup to prove the working principle.
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