Fig. 2. Active control of anisotropy in h-SRR metasurface.

a Schematic illustration of the h-SRR metasurface being pumped by near-infrared femtosecond pulses. b Experimentally retrieved photoconductivity at various pump fluences for an unpatterned SOS substrate with a 0.6 μm thick silicon epilayer and a 460 μm thick sapphire substrate, and c the photocarrier excitation and relaxation dynamics of the silicon epilayer at a pump fluence of 1.9 mJ/cm². d Microscopic images of the fabricated h-SRR sample array with a zoomed-in image showing the details of an individual resonator with geometrical parameters (in μm) r₁ = 37, α₁ = 10°, metal width = 5, and square period = 80. e, f Experimental demonstration of all-optical active control of the anisotropy in terms of mode switching in the co- and cross-polarized transmission spectra; the 85% modulation is on the basis of the OFF state spectrum. g Resultant ultrafast modulation of the output polarization state in terms of ellipticity, and h calculated two output polarization ellipses (RCP and LP) in the “ON” and “OFF” states on the basis of experimental data