Satellite based imaging spectrometry is an important tool for earth observation. Most instruments use dispersive optics such as gratings to obtain spectral information.
This demands a certain minimal instrument size to provide the necessary optical path length. Filter based spectrometry allows smaller optical systems, but traditional filter designs generally only use fractions of the incoming light. Spectral filters based on photonic crystals show the potential for instruments with high total transmission while enabling further miniaturization. Development of this concept requires experimental investigation on the influence of the filter-detector distance on the spectral characteristics of the photonic crystals.
This work shows the development and demonstration of an experimental design that allows transmission measurements of filters as close as 40 μm from the detector.
Through combining the interference originating from the filter and detector surfaces forming a Fabry-Perot cavity with the spectral imaging data, 6-DoF position measurement of the filter is achieved. The design and measurement concept are demonstrated through a set of validation measurements, followed by transmission measurements on a filter sample over the 50-100 μm range with 5 μm spacing.