Spontaneous emission enhancement using hyperbolic metamaterials

Control of spontaneous emission, which is one of the fundamental concepts in the field of quantum optics, has been reported using photonic crystals and microcavities through the Purcell effect. Increasing the photonic density of states (PDOS) is the key to enhancing the spontaneous emission from emitters which have a low quantum yield. There have been several reports on the enhancement of spontaneous emission from QDs embedded in microcavities. In all of these demonstrations, the emitter and the emission was confined within the microcavity which enabled the greater interaction between the emitter and the cavity mode. In contrast, the system presented here does not rely on localization of electromagnetic field for increase in PDOS and thereby the enhancement in spontaneous emission. Instead, the metamaterial structure exploits the hyperbolic dispersion in the PDOS to create more states for the emitter to emit through. For a fixed frequency the wavevector for the anisotropic medium can take on arbitrary large values. In addition, the hyperbolic dispersion is achieved in a wide spectral range and is tolerant to deviations in the thickness of each of the constituent layers. One of the key differences in this approach versus the microcavity approach is the broadband nature of the enhancement. In microcavities the enhancement is observed only at the cavity resonant wavelength. In contrast, here the enhancement is observed over the entire emission spectrum of the quantum dots.