A general-purpose spectroscopic camera for single-board computers

Abstract

A low-cost consumer-grade spectroscopic system offers potential applications in many fields. Linear variable optical filters (LVOFs) placed in front of imaging sensors are one of the most promising avenues to realize this goal. In this work, we built a spectroscopic system by depositing an LVOF directly onto the protective window of OV5647 color and OV9281 monochrome imaging sensors for the Raspberry Pi. The ¼” sensors cost $15-$80 CAD at the time of writing and have linear dimensions of only 2.7 – 3.6 mm. To achieve a suitable gradient over such small sensors, an ultra-slow shutting system was built for the physical vapor deposition of an SiO2 gradient layer between two partially transparent silver mirrors to form a miniature LVOF. The resulting devices operated as effective low-cost spectrometers that were single-moded in the visible spectrum. These simple systems were finally used to measure spectra from sample light sources, clearly illustrating the advantages and limitations of this simple and economical approach towards everyday consumer spectroscopy.