We present a new concept for spatial scanning hyperspectral imaging. Spatial scanning is one of the main methods used for hyperspectral data acquisition and can provide high spectral resolution over a wide spectral range. However, conventional techniques, such as the whiskbroom and the pushbroom techniques, suffer from the need for relative motion between the target and the imaging system, which increases the complexity on the hardware side and limits the application possibilities. Our new approach combines a rotating slit and a co-rotating Dove prism. The rotating slit scans the target image by selecting one line from the image at each angular position of the slit. The rotating Dove prism is used to synchronously realign the transmitted light from the selected image line with respect to the transmission grating to allow the projection of the diffracted light over the same range of pixel columns of the image sensor to facilitate data acquisition and extraction of spectral information. The new approach enables the spatial scanning of the target image without the need for relative linear motion or the use of additional external equipment and therefore opens the door for more application scenarios.
Among the methods developed for hyperspectral imaging, pushbroom spatial scanning stands out when it comes to achieving high spectral resolution over a wide spectral range. However, conventional pushbroom systems are usually realized using passive system components, which has limited their flexibility and adaptability and narrowed their application scenarios. In this work, we adopt a different approach to the design and construction of pushbroom systems based on using active internal components. We present a new system concept utilizing an internal line scanning unit and a rotating camera mechanism. This enables a dual-mode imaging system that allows switching between 2D spatial imaging and spectral imaging. The line scanning unit, which consists of a narrow slit mounted to a linear piezo motor, facilitates the spatial scanning of the target while eliminating the laborious relative motion between the target and the imaging system, which is needed in conventional spectrographs. A software is developed for the automation and synchronization of the active components, which enables a novel feed-forward compensation function to compensate the shift in the diffraction angle due to the scanning motion of the slit and provide higher flexibility in data acquisition.
Porous silicon based rugate filters are emerging as interesting functionalized optical components in Micro-Opto-Electro-Mechanical Systems due to their specific nanostructures and superior optical properties. In this work, a cost-effective approach to generate a porous silicon based rugate filter wheel containing nine filter segments in the visible wavelength range suitable for multispectral imaging systems is presented. The filter wheel segments are patterned on a silicon wafer using silicon nitride insulating masks and generated using the anodization technique. Specific characteristics of filter segments are adjusted by the current squeezing effect during the anodization through the geometrical size of the filter segments, which results in local current redistributions and consequently porous silicon formation rate and porosity modifications. A finite element model made in COMSOL Multiphysics is also presented to study redistributions of the current density and the current squeezing effect during the anodization for the proposed filter wheel. The proposed filter wheel can be miniaturized and integrated into a portable multispectral imaging system.
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