Topological phase transition in wire medium enables high Purcell factor at infrared frequencies

In this paper, we study topological phase transition in a wire medium operating at infrared frequencies. This transition occurs in the reciprocal space between the indefinite (open-surface) regime of the metamaterial to its dielectric (closed-surface) regime. Due to the spatial dispersion inherent to wire medium, a hybrid regime turns out to be possible at the transition frequency. Both such surfaces exist at the same frequency and touch one another. At this frequency, all values of the axial wavevector correspond to propagating spatial harmonics. The implication of this regime is the overwhelming radiation enhancement. We numerically investigated the gain in radiated power for a sub-wavelength dipole source submerged into such the medium. In contrast to all previous works, this gain (called the Purcell factor) turns out to be higher for an axial dipole than for a transversal one.

Topological transition in a nanowire medium and its radiative implication

We reveal and study the topological transition in a metamaterial formed by parallel nanowires of polaritonic material. When the dispersion transits from the elliptic (epsilon-positive) to hyperbolic (epsilon-indefinite) regime, a very specific isofrequency surface arises which implies an extraordinary Purcell factor in spite of noticeable optical losses.