In this paper we demonstrate that asymmetric hyperbolic metamaterials (AHM) can produce strongly directive thermal emission in far-field zone, which exceeds Plancks limit. Asymmetry is inherent in an uniaxial medium, whose optical axes are tilted wit
h respect to medium interfaces and appears as a difference in properties of waves, propagating upward and downward with respect to the interface. Its known that a high density of states (DOS) for certain photons takes place in usual hyperbolic metamaterials, but emission of them into a smaller number in vacuum is preserved by the total internal reflection. However, the use of AHM enhance the efficiency of coupling of the waves in AHM with the waves in free space that results in Super-Planckian far-field thermal emission in certain directions. Different plasmonic metamaterials can be used for realization of AHM. As example, thermal emission from AHM, based on graphene multilayer, is discussed.
In this paper we introduce a generalized concept of field-transforming metamaterials, which perform field transformations defined as linear relations between the original and transformed fields. These artificial media change the fields in a prescribe
d fashion in the volume occupied by the medium. We show what electromagnetic properties of transforming medium are required. The coefficients of these linear functions can be arbitrary scalar functions of position and frequency, which makes the approach quite general and opens a possibility to realize various unusual devices.
