Monolithic all-silicon flat lens for broadband LWIR imaging.

We designed, fabricated, and characterized a flat multi-level diffractive lens comprised of only silicon with diameter=15.2mm, focal length=19mm, numerical aperture of 0.371, and operating over the long-wave infrared (LWIR) spectrum=8µm to 14 µm. We experimentally demonstrated a field of view of 46°, depth of focus >5mm, and wavelength-averaged Strehl ratio of 0.46. All of these metrics were comparable to those of a conventional refractive lens. The active device thickness is only 8 µm, and its weight (including the silicon substrate) is less than 0.2 g.