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High-efficiency, linear-polarization-multiplexing metalens for long-wavelength infrared light.

Variable-focus lenses are essential elements of optical systems with extensive applications in microscopy, photography, and optical detection. However, conventional varifocal optical systems obtain a limited tunable capability at the expense of bulk size and slow speed. The metasurfaces are two-dimensional flat structures composed of subwavelength scatterers that exhibit the strong potential for developing ultrathin optics. Here we propose and experimentally demonstrate an all-dielectric polarization-multiplexing metalens with the capability to selectively focus polarized light. The focal length can be controlled by altering the linear polarization state of the incident light. The metalens has focusing efficiencies higher than 72% and exhibits nearly diffraction-limited focusing at long-wavelength infrared frequency. In addition, it is easy to realize high throughput with low manufacturing cost due to the use of complementary metal oxide semiconductor-compatible processes. We envision that this type of polarization-dependent device may pave the way towards the development of compact, multifunctional, and tunable optics.