Fig. 1. (a) Schematic view of a GSS illustrated by two counter-propagating and coherently modulated input beams (I+ and I−), with O+ and O− being the output beams. (b) Equivalent circuit model of the GSS.

Fig. 2. Coherent absorption of GSS for plane wave versus frequency under different Fermi levels. The solid line represents the 3D full wave simulation results and dotted line means the equivalent circuit calculated results.

Fig. 3. Two-dimensional false-color plot of the calculated coherent absorption as a function of Fermi level and phase modulation. (a) Equivalent circuit calculated results and (b) simulated results.

Fig. 4. (a) and (b) Calculated coherent absorption under TE/TM incident illumination, where the dashed lines denote the condition of EF=0.22  eV. (c) CPA Fermi-level dispersion at an oblique incidence for TE polarization (red solid curve) and TM polarization (blue solid curve).

Fig. 5. Coherent absorption of N-layers stacked GSS versus Fermi energy. Insert graph is the schematic of stacked GSS illuminated by two counter-propagating input beams. Solid curves represent the equivalent circuit calculated results and triangles refer to the full-wave simulation results.

Fig. 6. (a) Optical image of graphene on a PVC substrate. (b) Raman spectrum of monolayer graphene. (c) Fabricated GSS device. (d) Configuration of the waveguide measurement setup. (e) Relation between the Fermi level of graphene and bias voltage.

Fig. 7. (a) Measured (circles) and calculated (solid lines) coherent absorptivities of GSS in the waveguide system under different bias voltages. (b) A 2D false-color plot of the coherent absorptivity as a function of frequency and phase modulation (U=3 V). (c) Coherent absorption of single- or multilayered GSS versus bias voltage (f=4.27  GHz).