Abstract

The spectral band covering ${\sim}{8 {-} 12}\;\unicode{x00B5}{\rm m}$ is atmospherically transparent and therefore important for terrestrial imaging, day/night situational awareness systems, and spectroscopic applications. There is a dearth of tunable filters spanning the band. Here, we propose and demonstrate a new, to the best of our knowledge, tunable-filter method engaging the fundamental physics of the guided-mode resonance (GMR) effect realized with a non-periodic lattice. The polarization-dependent filter is fashioned with a one-dimensional Ge grating on a ZnSe substrate and interrogated with a ${\sim}{1.5}\;{\rm mm}$ Gaussian beam to show clear transmittance nulls. To expand the tuning range, the device parameters are optimized for sequential operation in TM and TE polarization states. The theoretical model exhibits a tunable range exceeding 4 µm, thus covering the band fully. In the experiment, a prototype device exhibits a spectral range of 8.6–10.0 µm in TM and 9.9–11.7 µm in TE polarization or ${\gt}{3}\;\unicode{x00B5}{\rm m}$ total. With additional efforts in fabrication, we expect to achieve the full range.

© 2021 Optical Society of America

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