Space squeezing optics: Performance limits and implementation at microwave frequencies

Optical systems often largely consist of empty space as diffraction effects that occur through free-space propagation can be crucial for their function. Contracting these voids offers a path to the miniaturization wide range optical devices. Recently, new element—coined “spaceplate”—has been proposed, which is capable emulating over specified distance using thinner non-local metamaterial [Reshef et al., Nat. Commun. 12, 3512 (2021)]. The compression factor such an element given by ratio length replaced thickness spaceplate itself. In this work, we test prototype in microwave spectral region (20–23 GHz)—the first demonstration designed operate ambient air. Our device consists Fabry–Pérot cavity formed from two reflective metasurfaces with tuned varying size perforations within each layer. Using pair directive horn antennas, measure up ∼6 numerical aperture (NA) 0.34 and fractional bandwidth 6%. We also investigate fundamental trade-offs exist between factor, transmission efficiency, NA, single resonator design highlight it reach arbitrarily high factors restricting its NA bandwidth.