Significance: The ability to perfectly absorb light with optically thin materials poses a significant challenge for many applications such as camouflage, light detection, and energy harvesting. Current designs require planar reflectors that crack and delaminate after heating or flexing. Moreover, they cannot be transferred to more desirable substrates for mechanically flexible and low-cost applications. Although particulate-based materials overcome these challenges, broadband absorption from standalone systems has not been demonstrated. Here, a class of materials, transferrable hyperbolic metamaterial particles (THMMP), is introduced. When closely packed, these materials show broadband, selective, omnidirectional, perfect absorption. This is demonstrated with nanotubes made on a silicon substrate that exhibit near-perfect absorption at telecommunication wavelengths even after being transferred to a mechanically flexible, visibly transparent polymer.

When engineered on scales much smaller than the operating wavelength, metal-semiconductor nanostructures exhibit properties unobtainable in nature. Namely, a uniaxial optical metamaterial described by a hyperbolic dispersion relation can simultaneously behave as a reflective metal and an absorptive or emissive semiconductor for electromagnetic waves with orthogonal linear polarization states. Using an unconventional multilayer architecture, we demonstrate luminescent hyperbolic metasurfaces, wherein distributed semiconducting quantum wells display extreme absorption and emission polarization anisotropy. Through normally incident micro-photoluminescence measurements, we observe absorption anisotropies greater than a factor of 10 and degree-of-linear polarization of emission >0.9. We observe the modification of emission spectra and, by incorporating wavelength-scale gratings, show a controlled reduction of polarization anisotropy. We verify hyperbolic dispersion with numerical simulations that model the metasurface as a composite nanoscale structure and according to the effective medium approximation. Finally, we experimentally demonstrate >350% emission intensity enhancement relative to the bare semiconducting quantum wells.

We present a formal treatment of the modification of spontaneous emission rate by a cavity (Purcell effect) in sub-wavelength semiconductor lasers. To explicitly express the assumptions upon which our formalism builds, we summarize the results of non-relativistic quantum electrodynamics (QED) and the emitter-field-reservoir model in the quantum theory of damping. Within this model, the emitter-field interaction is modified to the extent that the field mode is modified by its environment. We show that the Purcell factor expressions frequently encountered in the literature are recovered only in the hypothetical condition when the gain medium is replaced by a transparent medium. Further, we argue that to accurately evaluate the Purcell effect, both the passive cavity boundary and the collective effect of all emitters must be included as part of the mode environment.

The first generation of hyperbolic metamaterials, metasurfaces, and naturally hyperbolic materials (HMMs) utilized the static and passive properties of their constituent metallic and dielectric components to achieve intriguing macroscopic behavior, such as imaging and focusing of light below the diffraction limit and the broadband modification to the rate of spontaneous emission. While promising, and operating from RF frequencies to the ultraviolet, many potential applications of early HMMs were spoiled by inflexible operation and dissipation losses. Recently, the use of dynamically tunable and active constituent materials has increased, guiding HMMs into more functional regimes. In this review we survey the state-of-the-art of tunable and active electromagnetic HMMs. Based on a firm theoretical foundation, we review the most recent experimental work on hyperbolic dispersion endowed with a tunable or active character. Additionally, we review proposed ideas that may inspire new experimental work and offer a comparison to other photonic platforms.

A novel method is presented to outcouple high spatial frequency (large-k) waves from hyperbolic metamaterials (HMMs) without the use of a grating. This approach relies exclusively on dispersion engineering, and enables preferential power extraction from the top or from the side of a HMM. Multilayer (ML) HMMs are shown to be better suited for lateral outcoupling, while nanowire HMMs are the most convenient choice for top outcoupling. A 6-fold increase in laterally extracted power is predicted for a dipole–HMM system with a Ag/Si ML operating at λ = 530 nm, when metallic filling ratio is changed from an unoptimized to the optimized one. This new design concept supports the cost-effective mass production of high-speed HMM optical transmitters.

We theoretically consider the existence of multiple nonzero components of the second-order nonlinear susceptibility tensor, ${\chi }^{(2)}$, generated via strain-induced symmetry breaking in crystalline silicon. We determine that, in addition to the previously reported ${\chi }_{xxy}^{(2)}$ component, the ${\chi }_{yyy}^{(2)}$ component also becomes nonzero based on the remaining symmetry present in the strained material. In order to characterize these two nonlinearities, we fabricate Fabry–Perot waveguide resonators on 250 nm thick silicon-on-insulator wafers clad with 180 nm of compressively stressed ($-1.275\mathrm{GPa}$) silicon nitride. We measure the shifts in these devices’ modal effective indices in response to several bias electric fields and calculate the ${\chi }_{\text{eff},xxy}^{(2)}$ and ${\chi }_{\text{eff},yyy}^{(2)}$ nonlinear susceptibility tensor elements induced by the breaking of the guiding material’s inversion symmetry. Through the incorporation of finite element simulations encompassing the theoretical distribution of strain, the applied bias field, and the optical modes supported by the waveguide geometry, we extract two phenomenological scaling coefficients which relate the induced optical nonlinearities to the local strain gradient.