Spontaneous Emission inside a Hyperbolic Metamaterial Waveguide

The ability to control the rate of spontaneous emission via the design of nanostructured materials with appropriate electromagnetic properties is important in the development of novel fast sources of incoherent illumination, single photon emitters for quantum optical applications, laser physics, and de-excitation of electronic states leading to photodegradation in organic materials. Here, for an emitter placed inside a hyperbolic metamaterial slab of finite thickness comprised of an array of gold nanorods, we experimentally demonstrate an enhancement of the fluorescence coupled to the waveguided plasmon-polariton modes of the metamaterial. We show that fluorescence properties in such a finite-size metamaterial design behave differently from commonly studied infinite metamaterials or when the emitters are placed near the metamaterial interface. The emitters inside the metamaterial waveguide exhibit an almost 50-fold reduction of their lifetime, whereas a much smaller reduction (a factor of 2-3) is observed for emitters placed on top of the metamaterial. While in both cases the emission from the metamaterial can be radiated in the far field (up to 18% of the total emitted intensity, depending on the emitter position with respect to the nanorods), the coupling to waveguided modes of the metamaterial slab provides an efficient means to shape the emission spectrum for each polarization. The considered geometry is ideal for designing integrated, fast optical sources for data communications, sensing, or quantum photonic applications.