Dielectric Building Blocks Research Articles

Bio‐inspired photonic crystals: Tailoring the dielectric building blocks to control the light propagation

AbstractPhotonic crystals have drawn tremendous attention in recent years owing to their unique optical properties and remarkable advantages in various applications such as bioassays, sensors and optical devices. Benefiting from the spatially ordered structures, the flow of visible light can be manipulated by photonic crystals in a controlled manner. In this review, we summarize recent progress toward bio‐inspired photonic crystals, including techniques for the construction of spatially ordered structures in diverse dimensions for photonic crystals, and strategies to manipulate the periodicity of the dielectric building blocks to control the light propagation in the presence of external stimuli. We start with the description of structure induced colors in nature with a systematic investigation to reveal the derivation of these colors, followed by a discussion on the design and fabrication of various types of bio‐inspired photonic crystals by manipulating the arrangement of dielectric building blocks. We also highlight the stimuli responsive photonic crystals with tunable optical properties and their applications in sensing and color display.

Inverse design of broadband highly reflective metasurfaces using neural networks

Metamaterials exhibit optical properties not observed in traditional materials. Such behavior emerges from the interaction of light with precisely engineered subwavelength features built from different constituent materials. Recent research into the design and fabrication of metamaterial-based devices has established a foundation for the next generation of functional materials. Of particular interest is the all-dielectric metasurface, a two-dimensional metamaterial exploiting shape-dependent resonant features while avoiding losses through the use of dielectric building blocks. However, even this simple metamaterial class has a nearly infinite number of possible configurations; researchers now require new methods to efficiently explore these types of design spaces. In this work, we employ rigorous coupled wave analysis to calculate reflection and transmission spectra associated with a class of open-cylinder all-dielectric metasurface. By altering the geometric parameters of open-cylinder metasurfaces, we generate a sparse training data set and construct artificial neural networks capable of relating metasurface geometries to reflection and transmission spectra. Here, we successfully demonstrate that pseudo autodecoder neural networks can suggest device geometries based on a requested optical performance---inverting the design process for this metasurface class. As an example, we query for and discover a particular open-cylinder metasurface displaying a reflection band $R\ensuremath{\ge}99%$ centered at ${\ensuremath{\lambda}}_{0}=1550\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ that is much broader $\mathrm{\ensuremath{\Delta}}\ensuremath{\lambda}=450\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ than anything reported for optical metasurfaces. We then analyze the modal interplay in the open-cylinder metasurface to better understand the underlying physics driving the broadband behavior. Ultimately, we conclude that neural networks are ideally suited for generally approaching these types of complex inverse design problems.

On-Chip Integrated Single Photon Source-Optically Resonant Metastructure Based Scalable Quantum Optical Circuits

We present an approach to realizing on-chip optical quantum information processing (QIP) systems comprising (1) single photon source (SPS) arrays, here based on a new class of ordered single quantum dots of controlled size and shape named Mesa-top Single Quantum Dots (MTSQDs) that are naturally integrable in scalable architectures with (2) on-chip light manipulating units (LMUs) based upon either the conventional 2D photonic crystal platform or metastructures made of subwavelength size dielectric building blocks (DBBs) whose collective Mie-like optical resonances provide, simultaneously, all the needed light manipulating functions. The MTSQDs can provide high spectral uniformity with as-grown pairs emitting within $300\mu $ eV—thus calling for exploration of pathways for implementing on-chip SPS-SPS coupling for quantum entanglement. To this end, we present here simulation results for two different DBB-based implementations of scalable photon entanglement in MTSQD-DBB LMU coupled system.: (1) DBB array based nanoantenna-waveguide-beamsplitter-beamcombiner metastructures around the MTSQD SPSs that exploit primarily their collective magnetic dipole mode to simultaneously provide Purcell enhancement, enhanced emission directionality, waveguiding, beamspliting and beamcombining, thus enabling on-chip path entanglement via indirect coupling between the SPSs; (2) two MTSQDs coupled directly via the collective magnetic dipole mode of a back-to-back nanoantenna-waveguide structure. In either case, the long-distance coupled MTSQD-DBB structural units constitute the primitives for building complex quantum optical circuits.

Non-tapered metamaterial emitters for radiative cooling to low temperature limit

A selective thermal emitter is a requisite for approaching the radiative cooling limit, while the tapered metamaterial emitters, thus far, have difficulties in scalable manufacturing, hindering the field tests. In this work, we presented a methodology for designing the non-tapered metamaterial emitters without excluding the tapered and the inverted ones considering experimental imperfections. The bandwidths were not governed by the ratio of top to bottom width of arrays any more as conventional tapered metamaterials, while the non-tapered ones were only dependent on the width of vertical pillars and the thicknesses of dielectric building blocks. The sensitivity of the emission spectral characteristics of the non-tapered metamaterial emitters to the tilt of side walls was also investigated and the optimization strategy was proposed. The non-tapered metamaterial emitters could achieve an average emissivity of 0.8 at the atmospheric window with wavelengths of 8 to 13 μm, which would bring about a temperature reduction of 55 K in the absence of parasitic heat. The thickness-tailored bandwidth features in the non-tapered metamaterial emitters, which provided an in-depth insight into conventional tapered metamaterial emitters, mitigating complexities in practical production and paving the way for experimental access to more significant temperature reduction.

Mesa-top quantum dot single photon emitter arrays: Growth, optical characteristics, and the simulated optical response of integrated dielectric nanoantenna-waveguide systems

Nanophotonic quantum information processing systems require spatially ordered, spectrally uniform single photon sources (SPSs) integrated on-chip with co-designed light manipulating elements providing emission rate enhancement, emitted photon guidance, and lossless propagation. Towards this goal, we consider systems comprising an SPS array with each SPS coupled to a dielectric building block (DBB) based multifunctional light manipulation unit (LMU). For the SPS array, we report triggered single photon emission from GaAs(001)/InGaAs single quantum dots grown selectively on top of nanomesas using the approach of substrate-encoded size-reducing epitaxy (SESRE). Systematic temperature and power dependent photoluminescence (PL), PL excitation, time-resolved PL, and emission statistics studies reveal high spectral uniformity and single photon emission at 8 K with g(2)(0) of 0.19 ± 0.03. The SESRE based SPS arrays, following growth of a planarizing overlayer, are readily integrable with LMUs fabricated subsequently using either the 2D photonic crystal approach or, as theoretically examined here, DBB based LMUs. We report the simulated optical response of SPS embedded in DBB based nanoantenna-waveguide structures as the multifunctional LMU. The multiple functions of emission rate enhancement, guiding, and lossless propagation are derived from the behavior of the same collective Mie resonance (dominantly magnetic) of the interacting DBB based LMU tuned to the SPS targeted emission wavelength of 980 nm. The simulation utilizes an analytical approach that provides physical insight into the obtained numerical results. Together, the combined experimental and modelling demonstrations open a rich approach to implementing co-designed on-chip integrated SPS-LMUs that, in turn, serve as basic elements of integrated nanophotonic information processing systems.

Multifunctional all-dielectric nano-optical systems using collective multipole Mie resonances: toward on-chip integrated nanophotonics

We present an analysis of the optical response of a class of on-chip integrated nano-photonic systems comprising all-dielectric building block based multifunctional light manipulating units (LMU) integrated with quantum dot (QD) light sources. The multiple functions (such as focusing excitation light, QD emission rate enhancement, photon guidance, and lossless propagation) are simultaneously realized using the collective Mie resonances of dipole and higher order multipole modes of the dielectric building blocks (DBBs) constituting a single structural unit, the LMU. Using analytical formulation based on Mie theory we demonstrate enhancement of the excitation light simultaneously with the guiding and propagation of the emitted light from a QD emitter integrated with the DBB based LMU. The QD-DBB integrated structures can serve as the basic element for building nano-optical active circuits for optical information processing in both classical and quantum realms.

All-dielectric metamaterials.

The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.

Dielectric Genome of van der Waals Heterostructures.

Vertical stacking of two-dimensional (2D) crystals, such as graphene and hexagonal boron nitride, has recently lead to a new class of materials known as van der Waals heterostructures (vdWHs) with unique and highly tunable electronic properties. Ab initio calculations should in principle provide a powerful tool for modeling and guiding the design of vdWHs, but in their traditional form such calculations are only feasible for commensurable structures with a few layers. Here we show that the dielectric properties of realistic, incommensurable vdWHs comprising hundreds of layers can be efficiently calculated using a multiscale approach where the dielectric functions of the individual layers (the dielectric building blocks) are computed ab initio and coupled together via the long-range Coulomb interaction. We use the method to illustrate the 2D-3D transition of the dielectric function of multilayer MoS2 crystals, the hybridization of quantum plasmons in thick graphene/hBN heterostructures, and to demonstrate the intricate effect of substrate screening on the non-Rydberg exciton series in supported WS2. The dielectric building blocks for a variety of 2D crystals are available in an open database together with the software for solving the coupled electrodynamic equations.