Figure 4.

Reflective phase shifters with monolayer graphene for dynamic phase modulation. (a) Monolayer graphene is attached to the array of Al patches separated with the bottom Al film with an SU-8 spacer. (b) Gate-dependent reflection phase spectra of the combined structure when the Al patches have two sizes. Here, graphene as a lossy surrounding medium in sub-THz frequencies tunes the resonance intensity and phase. In each unit cell, the maximum phase change is ${180}^{°}$ around the resonance frequency by tuning the biasing voltage. By utilizing two types of unit cells with different resonance frequencies and working in the shaded frequencies, a ${360}^{°}$ phase change is accessible by tuning the biasing voltage. Reproduced with permission from [55], Copyright American Physical Society, 2015. (c) Graphene-tuned gold antenna array with back mirror. The zoom-in plot is the SEM image of the gold antennas with nanometer gaps. (d,e) Tunable absorption (d) and tunable reflection phase (e) for different graphene Fermi levels. The dielectric constant of graphene is sensitively modulated in the mid-IR, leading to a widely-tunable phase range of more than ${200}^{°}$ from $8.5\mathsf{\mu }\mathrm{m}$ to $8.7\mathsf{\mu }\mathrm{m}$. Reproduced with permission from [56], Copyright American Chemical Society, 2017.