  We propose an efficient multiband absorber comprising a truncated
one-dimensional periodic metal-dielectric photonic crystal and a reflective
substrate. The reflective substrate is actually an optically thick metallic
film. Such a planar device is easier to fabricate compared with the absorbers
with complicated shapes. For a 4-unit cell device, all of the four absorption
peaks can be optimized with efficiencies higher than 95%. Moreover, those
absorption peaks are insensitive to both polarization and incident angle. The
influences of the geometrical parameters along with the refractive index of the
dielectric on the device performance are discussed as well. Furthermore, it is
found that the number of absorption peaks within each photonic band exactly
corresponds to the number of the unit cells because the truncated photonic
crystal lattices have the function of selecting resonant modes. It is also
displayed that the total absorption efficiency gradually increases when there
are more metal-dielectric unit cells placing on top of the metallic substrate.
Our work is expected to have some potential applications in the areas of solar
energy harvesting and thermal emission tailoring.
