Mid-infrared high-resolution achromatic air-microlens in silicon

Infrared optics have garnered significant attention due to growing demand in advanced optical imaging, communication, detection, and sensing. Among various IR devices, microlenses and microlens arrays offer distinct advantages in integration capability, imaging precision, multifunctionality, and costeffective manufacturing. In this paper, we present a novel design of high-resolution achromatic microlens in the mid-IR region. Different from traditional high-refractive-index convex microlens embedded within low index background medium, the current design is a low-index air concave microlens embedded within high index silicon medium. The designed air microlens exhibits capabilities in high-resolution imaging (~ λ/6) and achromatic performance across the 3-5 μm midinfrared spectrum. The air microlens could be assembled in large area microlens arrays or as part of multi-lenses system. When combined with HgCdTe detector system placed on the focal plane, the air microlens can find promising application in high-resolution optical imaging and high-sensitivity photoelectric detection.