Broadband Achromatic Metalens in the Long-Wave Infrared Regime

Compared with conventional lenses, metalenses can offer smaller form factor, light weight and new functionality, and have become the focus of the recent investigations of metasurface. To date, quite a lot of studies have been reported for chromatic aberration correction of metalenses. Noting most work was carried out to satisfy the required group delay or dispersion by introducing sophisticated and integrated nanopillars, which are obtained using computationally intensive global search algorithms. Generally, the design is time-consuming. Here, we propose an alternative scheme, where metalens that corrects the chromatic aberration can be designed by optimizing the spectral degree of freedom C(ω), rather than relying on time-consuming algorithms. The proposed metalens is compatible with the complementary metal oxide semiconductor (CMOS) fabrication process. The numerically demonstrated metalens with a diameter of 200 μm and a numerical aperture (NA) of 0.24 has a small focal length fractional change (FLFC) of 4.1% over the wavelength of 9∼12 μm with an average efficiency of 51.7% in transmission mode. Moreover, the effect of fabrication deviations on the performance of the metalens is analyzed, showing critical dimension (CD) bias, sidewall angle and pillar height all have different levels of influence on the performance of the metalens.