Bragg supermirrors and polarization-state-dependent attenuation and amplification

The planewave reflection/transmission characteristics of two nanostructured thin films were investigated numerically. The thin films are: (i) a columnar thin film and (ii) a periodic multilayer whose unit cell consists of two different columnar thin films. The nanocolumns of these thin films were taken to be made from dissipative materials while the intercolumnar regions were filled with an active material. A combination of inverse and forward homogenization formalisms was employed to estimate the constitutive parameters of the thin films. By computing reflectances and transmittances, it was found that the thin films can simultaneously amplify s-polarized incident light and attenuate p-polarized incident light, or vice versa. This polarization-state-dependent attenuation and amplification phenomenon depends upon the angle of incidence and the thickness of the thin film. Furthermore, the periodic multilayer was found to exhibit the Bragg phenomenon in two generally distinct polarization-dependent spectral regimes for incident linearly polarized light. The presence of both dissipative and active materials allows the high reflectance to generally exceed unity for incident light of one linear polarization state but not for incident light of the other polarization state, in their respective Bragg regimes; however, transmittances are low in both Bragg regimes. That is, the chosen periodic multilayer is at best a good Bragg mirror for one linear polarization state and a Bragg supermirror for the other linear polarization state.