A MEMS (micro electro mechanical system) technology has been used to produce scanning grating chips which have a
tiltable plate with grating structures optimized for the 900nm ... 2500nm range as diffractive element. Based on these
chips different spectrometers and a hyper spectral imager have been realized for NIR-spectroscopic applications like
agricultural quality analysis, recycling and process control. Ongoing developments aim at the further reduction of size
and effort. Chip scale or wafer scale packaging technologies could help to shrink the complete spectroscopic system. The
integration of signal processing and evaluation routines opens new applications for a broad range of scientific and nonscientific
users.
Scanning photon microscopes (SPM), also known as laser scanning microscopes (LSM), are provided by several
commercial manufacturers, e.g. [1-4]. Technically they illuminate a sample with light from a laser light source which is
deflected in two directions. The reflected light is detected through a photo sensitive detector. From the position of the
laser spot and the detector signal the image of the sample is calculated. Applying a second detector behind an aperture
stop, bright and dark field images of the sample can be taken. Furthermore processes like fluorescence or RAMAN can
be initiated. If the sample or a kind of marker added to the sample creates a fluorescence or RAMAN signal from a
selected wavelength, the signal can be separated through an additional filter in front of the detector or a spectrometer
respectively. Doing this, interesting applications in the field of non destructive testing arise.
State of the art systems offer an optical resolution of 0.2...0.5 μm but they are bulky and expensive. In our new
approach we aim at a lower resolution of 5 ... 10 μm applying a small system size and less effort for installation and
usage. This aim can be reached using a 2d MEMS scanner mirror for the laser light deflection.
The test setup realized has a size of 20cm x 10cm x 5cm. A red semiconductor laser with 30mW has been used for
evaluation. An image area of 10mm x 10mm has been selected. 1000×1000 pixels were taken in accordance with 10μm optical resolution.
KEYWORDS: Sensors, Spectrometers, Signal processing, Bioalcohols, Digital signal processing, Signal detection, Near infrared, Control systems, Indium gallium arsenide, Microelectromechanical systems
Micro spectrometers have been realized by the use of MEMS based scanning grating chips several
years ago. The main advantage is the requirement of a single detector instead of a detector array for
micro spectrometers applying fixed gratings. Especially in the near infrared range beyond the
detection limit of silicon detectors, this can help to reduce the system costs significantly.
First measurements for test application have been performed successfully. Industrial applications
require wide spectral range, high long term stability and sufficient computation power in the system
itself to realize intelligent sensor heads for process monitoring and quality control.
Through the recent time, many details have been improved. Extended InGaAs detectors have been
used to extend the spectral range up to 2500nm. Improvements of the grating position readout
improved the wavelength stability of the system even under tough operation conditions. The
integration of faster digital signal processors opens the possibility to implement spectral evaluation
algorithms into the system itself.
Besides simple applications shown earlier like the selection of different kinds of plastic waste, now a
more quantitative analysis can be achieved. For example the ethanol content of liquor samples has
been measured and evaluated quantitatively.
"NIR Hyperspectral Imaging" is a universal tool to measure and control chemical properties of objects. The combination
of digital imaging and molecular spectroscopy exhibits a great benefit, especially for in- and on-line analysis. However, a
wide use is impeded at present due to the expensive and complex system approach. One reason is the high cost of two
dimensional InGaAs detector arrays, another one is the special glass that is used in the near infrared NIR.
In this paper a new approach for a NIR Imaging spectrometer is presented. The base of the new Pushbroom
Hyperspectral Imager is a micromechanical scanning device with an integrated diffraction grating. This MOEMS device
is made in a standard SOI fabrication process developed at Fraunhofer IPMS.1 2 3 For the Hyperspectral Imager, a new
all-reflective optical system based on a Schiefspiegler setup has been developed. The simulated optical configuration and
the achieved performance of the system will be presented.
"NIR Hyperspectral Imaging" is a universal tool to measure and control chemical properties of objects. The combination of digital imaging and molecular spectroscopy exhibits a great benefit, especially for in- and on-line analysis. However, a wide use is impeded at present due to the expensive and complex system approach. One reason is the high cost of two dimensional InGaAs detector arrays, another one is the special glass that is used in the near infrared NIR.
In this paper a new approach for a NIR Imaging spectrometer is presented. The base of the new Pushbroom Hyperspectral Imager is a micromechanical scanning device with an integrated diffraction grating. This MOEMS device is made in a standard SOI fabrication process developed at Fraunhofer IPMS. For the Hyperspectral Imager, a new all-reflective optical system based on a Schiefspiegler setup has been developed. The simulated optical configuration and the achieved performance of the system will be presented.
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