Mid-Infrared High-Resolution Achromatic Air Microlens in Silicon

Infrared (IR) optics have garnered significant attention due to growing demands 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 cost-effective manufacturing. We present a novel design of high-resolution achromatic microlens in the mid-IR region. Different from traditional high-refractive-index convex microlenses embedded within a low-index background medium, the current design is a low-index air concave microlens embedded within a high-index silicon medium. The designed air microlens exhibits capabilities in high-resolution imaging (\sim\lambda/6) and achromatic performance across the 3-5 μm mid-IR spectrum. The air microlens could be assembled in large-area microlens arrays or as part of multi-lens system. When combined with the HgCdTe detector system placed on the focal plane, the air microlens can find promising applications in high-resolution optical imaging and high-sensitivity photoelectric detection.