Fig. 1. Design of the open-loop twisted meta-molecule arrays. (a) Schematic diagram of the 2D meta-molecule with three arms which can be swung by an angle φ. (b) Top-view and side-view (insets) SEM images of the fabricated 2D and 3D meta-molecule arrays on the silica substrate (w). (c) Top-view and side-view SEM images of the fabricated free-standing 3D meta-molecule arrays without the substrate (w/o). (d) Simulated LCP and RCP transmission spectra of the two meta-molecule arrays without the silica substrate. (e) Calculated CD spectra versus the wavelength and φ. (f) Measured CD spectra of the meta-molecule arrays with and without the substrate. The lattice periods of simulated and experimental arrays are 1.2 and 1.4 μm, respectively. Scale bars: 1 μm.

Fig. 2. Analysis of the CD reversal. (a), (b) Top-view electric field distributions of the meta-molecule surfaces for φ=0° (at λ=1272  nm) and φ=80° (at λ=1268  nm) under the normal RCP and LCP light incidence. (c) Schematic diagram of the deformed twisted meta-molecules with φ=0°, φ=40°, and φ=80°. (d) Schematic diagram of the straight meta-molecules with φ=0°, φ=40°, and φ=80°. (e) Calculated CD spectra of straight meta-molecules in (d). Inset: top view of the meta-molecules. Here, the lattice period is 1.2 μm.

Fig. 3. Effect of RI of the symmetrical environmental medium on CD response. (a) CD spectra with different RIs of the environment. (b) Top-view electric field distributions of the meta-molecule surfaces for n=1.0 (at λ=1390  nm) and n=1.5 (at λ=2082  nm) under the normal RCP and LCP light incidence. (c) Simulated resonance wavelength versus the RI of the environment. (d) Simulated FoM under different RIs of the environment. Here, the lattice period is 1.4 μm.

Fig. 4. Effect of RIs of the unsymmetrical environmental medium on CD responses. (a) CD spectra with different nsup. (b) Top-view electric field distributions of the meta-molecule surfaces for nsup=1.0 (at λ=1730  nm) and nsup=1.5 (at λ=2070  nm) under the normal RCP and LCP light incidence. (c) Simulated resonance wavelength versus nsup. (d) Simulated FoM with different nsup. The lattice period is 1.4 μm.

Fig. 5. Experimental demonstrations of the RI sensing. (a) Schematic diagram of the experimental flow of RI sensing. (b), (c) Side-view SEM images of the 3D arrays after global irradiation. The lattice period is 1.4 μm. Scale bars: 2.5 μm. (d), (e) Simulated and measured CD spectra with refractive index liquids of different RIs. (f) Simulated and measured resonance wavelength versus the RI of the refractive index liquids with meta-molecules of H=250 and 400 nm, respectively. (g) Simulated CD response of meta-molecule array with different heights. The CD spectra of H=0, 250, and 400 nm are denoted by solid thick lines, solid thin lines, and dashed lines, respectively.