Design and fabrication of monolithically integrated metalens for higher effective fill factor in long-wave infrared detectors

Abstract Infrared imaging technology has been a worldwide research focus with various significant applications in the military and surveillance fields. Due to the complicated structure of the infrared imaging element, the photosensitive area only occupies quite a small part of each element, resulting in a low fill factor and thus limited utilization efficiency of incident light. By integrating a polarization-independent, wide-band focusing metalens into the imaging element of the long-wave infrared detector, the effective fill factor can be significantly improved. The monochromatic focusing efficiency of the metalens is up to 86%, and the average focusing efficiency in the wide spectral from 8 µm to 14 µm reaches 80%. The focusing measurement results demonstrate that the fabricated metalens can be used as a light concentrator to improve the detection sensitivity. The micro-optical metalens is flat and ultra-thin shaped, which is composed of sub-wavelength silicon pillars. Due to its compatibility with the detector manufacturing process, the metalens can be scaled up for a large micro-metalens array monolithically integrated with an infrared focal plane array(FPA).