Fabrication of Single-Layer Resonant Infrared Filters With High Optical Density

This study reports design, fabrication, and characterization of high-performance guided-mode resonance (GMR) infrared filters based on germanium (Ge) operating in the 7 to 15 µm spectral region. The single-layer GMR filters exhibit deep transmittance nulls and high sideband efficiency functioning as band-stop filters. There is reasonable agreement between experimental and theoretical spectral results. By modifying design parameters and incorporating an anti-reflection (AR) layer on the substrate backside, the functionality of the filter is significantly enhanced. The measured low transmittance value of the fabricated filters is found to be as low as 0.021% corresponding to an optical density of OD = 3.68. The results highlight the potential of GMR technology operating at long infrared wavelengths to enable high performance filters with tunable spectral characteristics. Anticipated application domains include the fields of sensing, imaging, and spectroscopy.