Long-wave infrared magnetic mirror based on Mie resonators on conductive substrate

Metal films are often used in optoelectronic devices as mirrors and/or electrical contacts. In many such devices, however, the π-phase shift of the electric field that occurs upon reflection from a perfect electric conductor (for which a metal mirror is a reasonable approximation) is undesirable. This is because it results in the total electric field being zero at the mirror surface, which is unfavorable if one wishes for example to enhance absorption by a material placed there. This has motivated the development of structures that reflect light with zero phase shift, as these lead to the electric field having an anti-node (rather than node) at the surface. These structures have been denoted by a variety of terms, including magnetic mirrors, magnetic conductors, and high impedance surfaces. In this work, we experimentally demonstrate a long-wave infrared device that we term a magnetic mirror. It comprises an array of amorphous silicon cuboids on a gold film. Our measurements demonstrate a phase shift of zero and a high reflectance (of ∼90%) at a wavelength of 8.4 µm. We present the results of a multipole analysis that provides insight into the physical mechanism. Lastly, we investigate the use of our structure in a photodetector application by performing simulations of the optical absorption by monolayer graphene placed on the cuboids.