J. Opt. 15, 114003 (2013)

A hyperbolic metamaterial consisting of a stack of tilted graphene sheets can potentially form an ultrathin light absorber that is 100% efficient, according to calculations by scientists in Finland and Russia. Igor Nefedov and co-workers say that by tilting graphene sheets, it is possible to create an asymmetry and an effective relative permittivity of −1, so that neither upwards nor downwards propagating waves are reflected. In principle, this result implies that all light incident on the structure will be completely absorbed. The proposed design has two significant limitations, however. First, it is narrowband, having an absorption bandwidth of only about 100–200 nm. Its centre wavelength depends on the design — reducing the intersheet spacing shifts operation to longer wavelengths in the infrared region. For example, designs with intersheet spacings of 5 nm, 3 nm and 1.5 nm are predicted to absorb radiation with wavelengths around 1.85 μm, 2.2 μm and 2.7 μm, respectively. A second limitation is that the approach is only effective for transverse-magnetic polarized light waves; it does not work for transverse-electric polarized waves. Although the design will be challenging to make, the researchers say that it should be possible to fabricate it using current technology.