  We demonstrate an efficient double-layer light absorber by exciting plasmonic
phase resonances. We show that the addition of grooves can cause mode splitting
of the plasmonic waveguide cavity modes and all the new resonant modes exhibit
large absorptivity greater than 90%. Some of the generated absorption peaks
have wide-angle characteristics. Furthermore, we find that the proposed
structure is fairly insensitive to the alignment error between different
layers. The proposed plasmonic nano-structure designs may have exciting
potential applications in thin film solar cells, thermal emitters, novel
infrared detectors, and highly sensitive bio-sensors.
