Figure 5. Elimination of birefringence by arraying the spirals in a configuration with C4 symmetry.
(a) A definition of the in-plane angle. (b) Top views and scanning electron microscope (SEM) images of the arrangements of the C1 and C4 metamaterials. The four spirals of the C4 metamaterial unit are arranged to have differing angles of rotation around the axis normal to the device surface, with angles of 0, π/2, π and 3π/2. (c) Spectra of the ellipticity angle ζ without averaging over the in-plane angle for the C1 metamaterial for six in-plane angles. All ellipticity spectra correspond to spirals with a centre deformed height of −53 μm. For a derivation procedure, see equations in Supplementary Note 3. (d) Spectra of the ellipticity angle ζ without averaging over the in-plane angle for the C4 device for six in-plane angles; the spirals have a centre deformed height of −53 μm. (e) Differential (Diff.) ellipticity angles η−η0 of the C4 spiral metamaterial.