Photonic-Cavity-Enhanced Laser Writing of Color Centers in Diamond.

Color centers in diamond have widespread utility in quantum technologies, but their creation process remains stochastic in nature. Deterministic creation of color centers in device-ready diamond platforms can improve the yield, scalability, and integration. Recent work using pulsed laser excitation has shown impressive progress in deterministically creating defects in bulk diamond.

Visible photon generation via four-wave mixing in near-infrared near-zero-index thin films.

Optical nonlinearities can be strongly enhanced by operating in the so-called near-zero-index (NZI) regime, where the real part of the refractive index of the system under investigation approaches zero. Here we experimentally demonstrate semi-degenerate four-wave mixing (FWM) in aluminum zinc oxide thin films generating radiation tunable in the visible spectral region, where the material is highly transparent. To this end, we employed an intense pump (787 nm) and a seed tunable in the NIR window (1100-1500 nm) to generate a visible idler wave (530-620 nm).

Modeling the optical properties of twisted bilayer photonic crystals.

We demonstrate a photonic analog of twisted bilayer graphene that has ultra-flat photonic bands and exhibits extreme slow-light behavior. Our twisted bilayer photonic device, which has an operating wavelength in the C-band of the telecom window, uses two crystalline silicon photonic crystal slabs separated by a methyl methacrylate tunneling layer. We numerically determine the magic angle using a finite-element method and the corresponding photonic band structure, which exhibits a flat band over the entire Brillouin zone.

Low-Loss Zero-Index Materials.

Materials with a zero refractive index support electromagnetic modes that exhibit stationary phase profiles. While such materials have been realized across the visible and near-infrared spectral range, radiative and dissipative optical losses have hindered their development. We reduce losses in zero-index, on-chip photonic crystals by introducing high- resonances via resonance-trapped and symmetry-protected states.

Dynamical Control of Broadband Coherent Absorption in ENZ Films.

Interferometric effects between two counter-propagating beams incident on an optical system can lead to a coherent modulation of the absorption of the total electromagnetic radiation with 100% efficiency even in deeply subwavelength structures. Coherent perfect absorption (CPA) rises from a resonant solution of the scattering matrix and often requires engineered optical properties. For instance, thin film CPA benefits from complex nanostructures with suitable resonance, albeit at a loss of operational bandwidth.

Optical Time Reversal from Time-Dependent Epsilon-Near-Zero Media.

Materials with a spatially uniform but temporally varying optical response have applications ranging from magnetic field-free optical isolators to fundamental studies of quantum field theories. However, these effects typically become relevant only for time variations oscillating at optical frequencies, thus presenting a significant hurdle that severely limits the realization of such conditions. Here we present a thin-film material with a permittivity that pulsates (uniformly in space) at optical frequencies and realizes a time-reversing medium of the form originally proposed by Pendry [Science 322, 71 (2008)SCIEAS0036-807510.

Dynamic Control of Nanocavities with Tunable Metal Oxides.

Fabry-Pérot metal-insulator-metal (MIM) nanocavities are widely used in nanophotonic applications due to their extraordinary electromagnetic properties and deeply subwavelength dimensions. However, the spectral response of nanocavities is usually controlled by the spatial separation between the two reflecting mirrors and the spacer's refractive index. Here, we demonstrate static and dynamic control of Fabry-Pérot nanocavities by inserting a plasmonic metasurface, as a passive element, and a gallium doped-zinc oxide (Ga:ZnO) layer as a dynamically tunable component within the nanocavities' spacer.

Enhanced Graphene Photodetector with Fractal Metasurface.

Graphene has been demonstrated to be a promising photodetection material because of its ultrabroadband optical absorption, compatibility with CMOS technology, and dynamic tunability in optical and electrical properties. However, being a single atomic layer thick, graphene has intrinsically small optical absorption, which hinders its incorporation with modern photodetecting systems. In this work, we propose a gold snowflake-like fractal metasurface design to realize broadband and polarization-insensitive plasmonic enhancement in graphene photodetector.

Controlling the Polarization State of Light with Plasmonic Metal Oxide Metasurface.

Conventional plasmonic materials, namely, noble metals, hamper the realization of practical plasmonic devices due to their intrinsic limitations, such as lack of capabilities to tune in real-time their optical properties, failure to assimilate with CMOS standards, and severe degradation at increased temperatures. Transparent conducting oxide (TCO) is a promising alternative plasmonic material throughout the near- and mid-infrared wavelengths. In addition to compatibility with established silicon-based fabrication procedures, TCOs provide great flexibility in the design and optimization of plasmonic devices because their intrinsic optical properties can be tailored and dynamically tuned.

Optical absorption of hyperbolic metamaterial with stochastic surfaces.

We investigate the absorption properties of planar hyperbolic metamaterials (HMMs) consisting of metal-dielectric multilayers, which support propagating plane waves with anomalously large wavevectors and high photonic-density-of-states over a broad bandwidth. An interface formed by depositing indium-tin-oxide nanoparticles on an HMM surface scatters light into the high-k propagating modes of the metamaterial and reduces reflection. We compare the reflection and absorption from an HMM with the nanoparticle cover layer versus those of a metal film with the same thickness also covered with the nanoparticles.