Fig. 3
a The periodic structure of four graphene blocks. b Three-dimensional diagram of the maximum absorption with incident light Φ and refractive index nd of the dielectric. c The absorption spectrum at positions @(2.3, 10), @(4.3, 10) and @(7.3, 10) of (b), respectively. d The FDTD numerical absorption spectrum with the Fermi level of graphene changing from 0.5 to 1.1 eV (n = 2)