A High Throughput Tunable Filter Module for Multispectral Imaging

Tunable filters are vital not only for dynamic display but also in the miniaturized spectral imaging system. Yet, the present tunable devices possess low optical throughput, bulky volume, slow response, or complex configuration. In this paper, the study proposed and experimentally demonstrated a compact tunable filter module based on metagratings combined with liquid crystals (LC). By the synergetic effect between the birefringent LC and the dichroic metagratings, the module possesses distinct transmissive features by electrically tuning the LC material, resulting from the polarization interference effect. A simple nanoimprinting method, which is suitable for the mass production of nanostructures is adopted for low-cost fabrication. These unique features endow the present tunable filter module with low cost, high optical throughput, and compact volume. As a proof of concept, a multispectral imager is built with this filter based on a commercial microscope. Experimental results show the system response is five times higher in optical throughput across the whole visible region than the traditional liquid crystal tunable filter and the signal-to-noise ratio can be improved by 7 dB. Considering the feasibility of nanoimprinting, this module paves the way for spectral imaging in low-light conditions and on-site scenarios such as tongue diagnosis and food quality inspection. In this paper, the study proposed and experimentally demonstrated a compact, low-cost tunable filter module based on metagratings combined with liquid crystals (LC). It shows an optical throughput five times higher than the traditional liquid crystal tunable filter and better spectrum reconstruction performance in the low-light condition.image