Active metasurface designs for lensless and detector-limited imaging

The emergence of metasurfaces has enabled lightweight, compact imaging with degrees of freedom which previously required complex optical setups to achieve, such as polarization, wave vector, and spectrum. To date, most metasurface-enabled imaging systems have thus far been 'passive', and therefore subject to fundamental information and thickness limits set by the coupling of light to their sensor arrays. We discuss the use of active metasurfaces in low form-factor and low pixel-count imaging systems and introduce a prototypical lensless imaging system concept which employs an active metasurface as a high-frequency, continuously tunable amplitude and phase modulation aperture, coupled to a discrete single-pixel detector. We analyze the scalability of such a platform and computationally demonstrate that a scalable 'perimeter-control' addressing architecture - in which a M × N rectangular array of scattering elements is addressed by only M + N voltages - is sufficient for image collection, even when scatterers exhibit limited $\left({272}^{◦}\right)$ phase control, and undesired amplitude variations. We also address fundamental limits in information collection, image aberrations, and signal-to-noise ratio, highlighting key advantages, limitations, and trade-offs for active metasurface imaging. We generalize our discussion to other active metasurface-enabled imaging configurations and applications. Finally, we consider promising active metasurface material platforms with an outlook towards new directions to enable high-efficiency imaging.