Perfectly asymmetric reflection enables unidirectional emission in a phonon-polariton (reststrahlen-band) material platform

Highly asymmetric effects in the photonic responses of structured materials have been attracting increasing attention recently, since they enable a higher degree of directional diversion of light that is conducive to application specific demands. We explore here a particular type of an asymmetric photonic response that is related to the system's reflectance profile. We show that the asymmetric reflectance profile of a photonic system can be tuned with an appropriate synergistic control of the geometric-structure asymmetry and the intrinsic material dissipation. Even extreme, near-perfect reflector materials can be sculpted so that reflection is almost totally suppressed for light incident from one-side while the structure maintains the near-perfect reflector property for light incident from the other side. We demonstrate this effect with a platform comprising a phonon-polariton material, in particular SiC, which in bulk form repels light within the reststrahlen-band spectrum. We subsequently explain, how as a consequence of Kirchhoff's law, the aforementioned asymmetric reflection response enables such platform to operate as a near-unidirectional emitter. We believe that these results are important for highly efficient one-way THz/infrared sources as well as passive radiative cooling devices.