Tunable Mid-Infrared Filters Based on Lithographically Fabricated Metal Meshes

Development of a high performance electronically tunable optical filter for the mid-infrared abling technology for spectral imaging, chemical vapor sensing and numerous other remote sensing applications. Tunable Fabry-Perot (F-P) filters have desirable features of high throughput (much needed in the mid-IR region where detectors are of low sensitivity), high resolution, fast-scanning capability, and applicability to 2-D scene spectral imaging. However, F-P filters are difficult to fabricate for the mid-IR region. Homogeneous metal films cannot be used due to high absorptivity, and multi-layer dielectric films are difficult to fabricate, are limited by available materials, and may not exhibit sufficiently high reflectance for desired high finesse. This project offers a novel approach to the development of tunable F-P filters for the mid-IR spectral range. The properties of the proposed F-P are essentially independent of fabrication material, but are instead dependent on the geometrical pattern and its dimensions. Furthermore, the proposed fabrication technique uses standard lithographic methods, which impart cost efficiency and excellent quality control. In Phase I, test filter elements will be fabricated and transmission properties of a breadboard tunable filter will be measured and compared to theoretical expectations. This technology will enable fabrication of low cost/high performance tunable infrared filters for the addition of spectral selectivity to numerous sensing platforms.