Studies on the tailored light transport and emission using dielectric metasurfaces

Abstract

Integrating nanophotonics structures with quantum emitters and deterministically controlling its emission dynamics has gained a promising demand in photonic-and quantum-technologies. This is possible owing to the excitation of different types of electric and magnetic dipolar excitation in the nano-resonators that constitute the nanophotonic structure. These nano-resonators arranged in a two-dimensional plane, known as the metasurfaces, is emerged as a potential platform to engineer the light transport and emission. All-dielectric metasurfaces have shown unprecedented possibilities in controlling the light-matter interaction due to its structure-induced optical resonant modes. This includes manipulating the directionality of light scattering and confining the light field intensity within the nano-resonators. Integrating quantum emitters to metasurface allows tailoring its spontaneous emission intensity and rate, which is traditionally believed to be an immutable property of the emitter. In the quest for the generation of an on-demand quantum source of light, nitrogen vacancy (NV) centers in nanodiamond have attracted huge research interests due to its excellent optical and spin properties at room temperature. But its emission properties like spectral-dependent intensity and rate are required to be optimized for its efficient use in many applications based on NVs. Thus, it is required to engineer the spontaneous emission intensity and rate of NV center for quantum sensing, magnetometry, bio-markers, and quantum photonics. Coupling of NV centers to dielectric metasurface is one of the promising approaches by which emission dynamics can be controlled through the deterministic changes in the local density of optical states (LDOS) induced by the metasurfaces. Here, we have studied the low-index all-dielectric metasurfaces that are easy to fabricate at the desired resonance frequency. The metasurface exhibits optical resonances, which appear as dips in the reflectivity spectra measured using the state-of-the-art micro-reflectivity facility. The origin of resonances is due to the diffraction of light on the corrugated surface, which appears as a grating mode or due to the light trapped within the micro-spheres termed as the leaky mode. The experimental results are validated using the finite-difference time-domain simulations and theoretical calculations. These metasurfaces have shown light field confinement due to the associated resonances over a broad spectral range. The broad tunability of resonances associated with dielectric metasurfaces is discussed, which is useful for generating structural colors with applications in displays and nighttime traffic lights. These metasurfaces are further studied for manipulating light emission properties of emitters like nanodiamonds when coupled to resonances of the structures. The enhancement in the spontaneous emission intensity and rate of NV centers in nanodiamonds using the low-index dielectric metasurfaces are discussed. We have shown a two-fold enhancement in emission intensity and decrease (increase) in emission lifetime (rate) at the resonance in comparison to a reference sample. This confirms a faster emission decay which accounts for the increased LDOS at the resonance. The proposed all-dielectric metasurfaces are useful for applications in optical switching and on-demand single-photon generation. High-index all-dielectric metasurfaces are explored to achieve the Kerker effect with unidirectional light scattering, that led to breakthrough applications in photonics. We have demonstrated Kerker effect in silicon nano-disks arranged in a square symmetry wherein an enhanced forward scattering is optimized at the zero phonon line (ZPL) of a single NV center. The simulation and analytical calculations attest the presence of Kerker condition as a peak (dip) in transmission (reflection). The tunability of the Kerker condition is discussed with variation in the geometrical parameters of the structure. Here, we introduce a metasurface integrated single NV center as a single photon source for achieving huge decay rate enhancement with high emission directionality, enhancing LDOS at ZPL while suppressing other non-resonant features. These studies initiate to explore new insights with emitters as on-chip quantum light sources for imaging and sensing, routing Kerker conditions in quantum metasurfaces. The deterministic change in LDOS is also investigated using a stacked monolayer of micro-spheres constituting a three-dimensional (3D) photonic crystal with an inherent thickness variation. We discuss the role of finite-size effects in 3D photonic crystals that inadvertently modify LDOS using time-resolved decay rate measurements. A 34% contrast in the measured emission lifetimes at the stop gap is obtained in comparison to a wavelength outside the stop gap. The results manifest wavelength-dependent linear scaling of lifetimes with the finite size of the crystal domain. The precise single domain measurements result in a robust modification of lifetime in an otherwise weakly classified self-assembled 3D photonic crystal.