Figure 5.

Graphene nanoribbons for reflective wavefront shaping. (a) Graphene ribbon element on top of the dielectric/metal substrate. (b) Variation of reflectivity and phase with the ribbon width. Reproduced with permission from [47], Copyright The authors, 2015. (c) Smooth ${360}^{°}$ phase variation is covered by tuning the Fermi level of graphene, and it is shifted with a well-maintained shape from 4 THz to 6 THz. Adapted from [58], Copyright IOP Publishing Ltd., 2017. (d) Far away from the optimum frequency, the phase variation is either too sharp or too weak to use. Reproduced with permission from [59], Copyright IEEE, 2018. Wavefront shaping is possible by properly selecting the ribbon width at the fixed Fermi level from (b), or by individual gate control over an uniform graphene nanoribbon array following (c,d).