Polarization-independent infrared micro-lens array based on all-silicon metasurfaces.

The long-wavelength infrared (LWIR) micro-lens arrays, as one of the important components in wafer level thermal optics, have been applied for wavefront sensing, beam shaping, integral imaging, and other thermal optical applications. Recently, electromagnetic metasurfaces provide a promising platform for designing high-performance, lightweight and ultracompact optical elements. Here, we experimentally demonstrate a 60 × 60 transmissive type, polarization-independent LWIR micro-lens array based on all-silicon metasurfaces with a fill factor approaching 100%. Each single micro-metalens with a pitch of 100 μm and a focal length of 100 μm operating at λ = 10.6 μm, can focus the light to a spot with a full-width at half-maximum (FWHM) of 12.7 μm (~1.2λ) at the focal plane. Considering the fact of single-step photolithography and standard integrated circuit (IC) compatible fabrication processes, these metasurface-based micro-lens arrays may have great potentials in compact thermal imaging systems.