  Subwavelength diffractive optics known as meta-optics have demonstrated the
potential to significantly miniaturize imaging systems. However, despite
impressive demonstrations, most meta-optical imaging systems suffer from strong
chromatic aberrations, limiting their utilities. Here, we employ inverse-design
to create broadband meta-optics operating in the long-wave infrared (LWIR)
regime (8 - 12 $\mu$m). Via a deep-learning assisted multi-scale differentiable
framework that links meta-atoms to the phase, we maximize the
wavelength-averaged volume under the modulation transfer function (MTF) of the
meta-optics. Our design framework merges local phase-engineering via meta-atoms
and global engineering of the scatterer within a single pipeline. We
corroborate our design by fabricating and experimentally characterizing
all-silicon LWIR meta-optics. Our engineered meta-optic is complemented by a
simple computational backend that dramatically improves the quality of the
captured image. We experimentally demonstrate a six-fold improvement of the
wavelength-averaged Strehl ratio over the traditional hyperboloid metalens for
broadband imaging.
