Photonic Gap Research Articles

Polariton Condensation in Gap-Confined States of Photonic Crystal Waveguides.

The development of patterned multiquantum well heterostructures in GaAs/AlGaAs waveguides has recently made it possible to achieve exciton-polariton condensation in a topologically protected bound state in the continuum (BIC). Polariton condensation was shown to occur above a saddle point of the two-dimensional polariton dispersion in a one-dimensional photonic crystal waveguide. A rigorous analysis of the condensation phenomenon in these systems, as well as the role of the BIC, is still missing. In the present Letter, we theoretically and experimentally fill this gap by showing that polariton confinement resulting from the negative effective mass and the photonic energy gap in the dispersion play a key role in enhancing the relaxation toward the condensed state. In fact, our results show that low-threshold polariton condensation is achieved within the effective trap created by the exciting laser spot, regardless of whether the resulting confined mode is long-lived (polariton BIC) or short-lived (lossy mode). In both cases, the spatial quantization of the polariton condensate and the threshold differences associated to the corresponding state lifetime are measured and characterized. For a given negative mass, a slightly lower condensation threshold from the polariton BIC mode is found and associated to its reduced radiative losses, as compared to the lossy one.

Magnetic-Fluorescent Responsive Janus Photonic Crystal Beads for Self-Destructive Anti-counterfeiting.

In this study, we fabricate magnetic-fluorescent responsive Janus photonic crystal beads (JPCBs) based on poly(styrene-methyl methacrylate-acrylic acid) (p(St-MMA-AA)) colloidal nanoparticles, Fe3O4, and photobase generators used for self-destructive anti-counterfeiting. We synthesize two kinds of photobase generators that can react with fluorescamine to produce various fluorescence colors. A microfluidic method is used to obtain the Janus photonic crystal beads. The upper portions of the JPCBs are photonic crystals assembled with colloidal spheres, whereas the Fe3O4 settles down to the bottom of the JPCBs due to its higher density. Photobase generators are distributed in photonic crystal gaps. Because of the magnetism of the Fe3O4, the JPCBs could be flipped from one side to the other in the presence of a magnet. After being exposed to UVC light and fluorescamine, the JPCBs can fluoresce under UVA light. Then, we create Janus microbeads arrays with various types of beads and apply them to the visitor card, bracelet, and box label to provide irreversible and self-destructive anti-counterfeiting. The JPCBs are capable of being encoded and angle-independently displayed, which are crucial to their applications in anti-counterfeiting, information coding, and array display.

Long-lived qubit entanglement by surface plasmon polaritons in a Weyl semimetal

We investigate spontaneous entanglement of two qubits mediated by nonreciprocal surface plasmon polaritons (SPPs) in a Weyl semimetal. In the absence of external magnetic fields, the topology of the Weyl semimetal even gives rise to nonreciprocal SPPs that are topologically protected and reside inside the photonic gap. We utilize this nonreciprocal SPP as a mediator of entanglement of two spatially separated qubits. Our two main findings are (1) the nonreciprocal SPP gives better quantum entanglement than the reciprocal one, and (2) the entanglement achieved in the Weyl semimetal is sufficiently long lived compared to the entanglement using SPPs in conventional metals.

High sensitivity and enhanced measurement range biosensing based on defective photonic crystal microring resonators

In this paper, we propose a defective photonic crystal microring resonator (DPhCMRR) by introducing a point defect into a conventional photonic crystal microring resonator (PhCMRR). The defective resonant wavelength within the photonic mode gap and the location of the defect mode distribution can be readily controlled. Unlike conventional PhCMRR, where the free spectral range (FSR) is limited by the dispersive band structure, our DPhCMRR can take advantage of the tunability of the defect mode within the photonic mode gap, leading to a significant increase of the measurement range. Moreover, the bulk refractive index sensitivity can reach 200 nm/RIU (refractive index unit) and the local refractive index sensitivity is about 5 to 10 times larger than that of the conventional PhCMRR. For sensing applications, our DPhCMRR can possess high sensitivity and wide measurement range simultaneously. As proof of principle, it is demonstrated that our proposed DPhCMRR can perform as a sensitive virus biosensor, which can detect a single virus and a concentration of viruses quantitatively. Therefore, our DPhCMRRs can provide a new platform for achieving high sensitivity and wide measurement range biosensing.

Location and Topology of the Fundamental Gap in Photonic Crystals

The fundamental, or first, band gap is of unmatched importance in the study of photonic crystals. Here, we address precisely where this gap can be opened in the band structure of three-dimensional photonic crystals. Although strongly constrained by symmetry, this problem cannot be addressed directly with conventional band-symmetry analysis due to the existence of a photonic polarization vortex at zero frequency. We develop an approach for overcoming the associated symmetry singularity by incorporating fictitious, auxiliary longitudinal modes. Our strategy also enables us to extend recent developments in symmetry-based topological analysis to the fundamental gap of three-dimensional photonic crystals. Exploiting this, we systematically study the topology of the minimal fundamental gaps. This reveals the existence of topological gap-obstructions that push the fundamental gap higher than what a conventional analysis would suggest. Our work demonstrates that topology can play a crucial role in the opening of the fundamental photonic gap and informs future theoretical and experimental searches for conventional and topological band gaps in three-dimensional photonic crystals.

Hybrid epsilon-near-zero modes of photonic gap antennas

We demonstrate that in photonic gap antennas composed of an epsilon-near-zero (ENZ) layer embedded within a high-index dielectric, hybrid modes emerge from the strong coupling between the ENZ thin film and the photonic modes of the dielectric antenna. These hybrid modes show giant electric field enhancements, large enhancements of the far-field spontaneous emission rate, and a unidirectional radiation response. We analyze both parent and hybrid modes using quasinormal mode theory and find that the hybridization can be well understood using a coupled oscillator model. Under plane-wave illumination, hybrid ENZ antennas can concentrate light and achieve local electric field amplitudes more than two orders of magnitude greater than that of the incident wave. This places them on par with the best plasmonic antennas. In addition, the far-field spontaneous emission rate of a dipole embedded at the antenna hotspot can be increased by more than three orders of magnitude as compared to that in free space, with nearly perfect unidirectional emission.

Polymer-based self-assembled photonic crystals to tune light transport and emission.

The advent of photonic crystals has made possible the idea of controlling flows of light, which has revolutionized photonics-based technology. Photonic crystals are constructed based on periodic refractive index variations in one-, two-, or three-spatial dimensions on the optical-wavelength scale. Photonic crystals show inherent photonic stop gaps or band gaps depending upon the crystal symmetry and refractive index contrast. Showing ease of fabrication, polymer-based self-assembled photonic crystals with stop gaps have been widely explored. We discuss angle- and polarization-dependent stop gap creation and splitting at higher angles of incidence. The observed stop gaps in self-assembled photonic crystals often deviate from theoretical predictions due to experimental constraints, such as finite size and fabrication disorders associated with samples. We perform micro-reflectivity experiments on a single domain, showing minimal disorder, with nearly 100% reflectivity, which is in agreement with theory. We obtain more than 75% emission intensity suppression and a 30% increase in the emission lifetime at the stop gap using micro-emission experiments in a single domain. This enables us to study the role of finite-size effects in photonic crystals in modifying the emission properties. We observe the linear scaling of the emission intensity suppression and the emission rate with the finite size of the crystal. Our single-domain experimental studies reveal that the use of low index-contrast self-assembled photonic crystals is a potential platform for strategically modifying light transport and emission properties.

Ultrafast dynamic nonlinear phenomena and mechanisms of photonic crystals over photonic gap and band regions

We systematically investigate ultrafast dynamic nonlinear mechanisms of photonic crystals (PhCs) with femtosecond (fs) pumping via the transmission change of a signal pulse. The pumping causes a nonlinear decrease (or increase) in the dielectric constant of the PhC material. A new phenomenon of the asymmetric change in the transmission spectra was observed in the gap region and the band-gap edge modes. For the band region, a sloped change in the transmission spectra was observed, and for the transition region, a hybrid of the two was observed. In addition, a universal dynamic picture of the fs nonlinear responses of the PhC was constructed.

Photonic Band Gap and Light Routing in Self-Assembled Lattices of Epitaxial Ge -on- Si Microstructures

The emergence of a photonic band gap in $\mathrm{Ge}$-on-$\mathrm{Si}$ micropillars ordered in a two-dimensional square lattice is demonstrated by the finite-element method. Candidate architectures are fabricated through epitaxy and the opening of the photonic band gap experimentally proved by photoluminescence spectroscopy. When the direct-gap emission of $\mathrm{Ge}$ is resonantly driven into the photonic gap, light propagation in the lattice plane is inhibited. Emission is eventually funneled out of plane, yielding a giant increase, i.e., about one order of magnitude, in the observed intensity. The demonstration of light routing in microcrystals' lattices opens interesting possibilities for $\mathrm{Si}$ photonics. The epitaxial self-assembled microstructures introduced here can be monotonically integrated on $\mathrm{Si}$ to improve the performances of group-IV lasers or engineered to optimize the working wavelength of future quantum photonic circuits.

Photonic Gap Antennas Based on High-Index-Contrast Slot Waveguides

Optical antennas made of low-loss dielectrics have several advantages over plasmonic antennas, including high radiative quantum efficiency, negligible heating and excellent photostability. However, due to weak spatial confinement, conventional dielectric antennas fail to offer light-matter interaction strengths on par with those of plasmonic antennas. We propose here an all-dielectric antenna configuration that can support strongly confined modes ($V\sim10^{-4}\lambda_{0}^3$) while maintaining unity antenna quantum efficiency. This configuration consists of a high-index pillar structure with a transverse gap that is filled with a low-index material, where the contrast of indices induces a strong enhancement of the electric field perpendicular to the gap. We provide a detailed explanation of the operation principle of such Photonic Gap Antennas (PGAs) based on the dispersion relation of symmetric and asymmetric horizontal slot-waveguides. To discuss the properties of PGAs, we consider silicon pillars with air or CYTOP as the gap-material. We show by full-wave simulations that PGAs with an emitter embedded in the gap can enhance the spontaneous emission rate by a factor of $\sim$1000 for air gaps and $\sim$400 for CYTOP gaps over a spectral bandwidth of $\Delta\lambda\approx300$ nm at $\lambda=1.25$ \textmu m. Furthermore, the PGAs can be designed to provide unidirectional out-of-plane radiation across a substantial portion of their spectral bandwidth. This is achieved by setting the position of the gap at an optimized off-centered position of the pillar so as to properly break the vertical symmetry of the structure. We also demonstrate that, when acting as receivers, PGAs can lead to a near-field intensity enhancement by a factor of $\sim$3000 for air gaps and $\sim$1200 for CYTOP gaps.

Circular swimming motility and disordered hyperuniform state in an algae system.

Active matter comprises individually driven units that convert locally stored energy into mechanical motion. Interactions between driven units lead to a variety of nonequilibrium collective phenomena in active matter. One of such phenomena is anomalously large density fluctuations, which have been observed in both experiments and theories. Here we show that, on the contrary, density fluctuations in active matter can also be greatly suppressed. Our experiments are carried out with marine algae ([Formula: see text]), which swim in circles at the air-liquid interfaces with two different eukaryotic flagella. Cell swimming generates fluid flow that leads to effective repulsions between cells in the far field. The long-range nature of such repulsive interactions suppresses density fluctuations and generates disordered hyperuniform states under a wide range of density conditions. Emergence of hyperuniformity and associated scaling exponent are quantitatively reproduced in a numerical model whose main ingredients are effective hydrodynamic interactions and uncorrelated random cell motion. Our results demonstrate the existence of disordered hyperuniform states in active matter and suggest the possibility of using hydrodynamic flow for self-assembly in active matter.

Stochastic modeling of 2D photonic crystals

Due to the fabrication processes, inaccurate manufacturing of the photonic crystals (PCs) might occur which affect their performance. In this paper, we examine the effects of tolerance variations of the radii of the rods and the permittivity of the material of the two-dimensional PCs on their performance. The presented stochastic analysis relies on plane wave expansion method and Mote Carlo simulations. We focus on two structures, namely Si-Rods PCs and Air-Holes PCs. Numerical results show—for both structures—that uncertainties in the dimensions of the PCs have higher impact on its photonic gap than do the uncertainties in the permittivity of the Si material. In addition, Air-Holes PCs could be a good candidate with least alteration in the photonic gap considering deviations that might occur in the permittivity of Si due to impurities up to 5%.

Transmittance spectrum of a double-period photonic structure composed of polymer materials

In this work, we calculate the transmittance spectrum within the THz range for a double-period photonic structure composed of polymer materials, whose dielectric constant is a function of the applied pressure. After applying the well-known Transfer Matrix Method, the numerical results reveal that increasing the sequence of the structure favors the appearance of a photonic gap, which exhibits a blueshift when the hydrostatic pressure increases. We also report a redshift in the photonic gap when the thickness of the polymer material layer increases at a fixed pressure value.

Sensitivity optimization of cells immersed in a cavity surrounded by thin graphene layers in one-dimensional photonic crystals

In this work, we used the transfer matrix method to calculate the transmittance spectrum for a defective one-dimensional photonic crystal with a cavity surrounded by graphene sheets into which Normal, Jurkat, HeLa, PC-12, MDA-MB-231, and MCF-7 cells are infiltrated. In the transmittance spectrum, the resonance modes for each cell were observed within the photonic gap. To optimize sensitivity, we modified the fill factor and cavity thickness parameters. As the fill factor increased, the position of the resonance modes moved toward longer wavelengths while their bandwidth decreased. In addition, a decrease in transmittance was observed, with a greater separation of the position of cancer cell resonance modes with respect to normal cells, thus increasing sensitivity up to 456 nm/RIU. Finally, we calculated the transmittance spectrum by increasing the thickness of the cavity while maintaining the fill factor constant at 0.4, obtaining a higher sensitivity of 560 nm/RIU.

Multichannel filtering properties of quaternary photonic crystals containing single-negative materials

One-dimensional quaternary photonic crystal (ABCD) $$^{N}$$ stacked by four kinds of single-negative materials is proposed, and the multichannel filtering properties of the structure (ABCD) $$^{N}$$ is investigated using the transfer matrix method. The result shows that a type of photonic gap named s-zero- $$\phi _{\mathrm {eff}}$$ gap that is similar to the zero- $$\phi _{\mathrm {eff}}$$ gap is found in the photonic structure. The multichannel filtering properties of the structures can be controlled by varying the period number, layer thickness, permittivity ( $$\varepsilon )$$ and permeability ( $$\mu )$$ . Moreover, the angular response of the filter is analyzed, which indicates that the bandgap of the structure is independent of the incident angle at the frequency is under 1.1 GHz. Thus it provides a new way to design tunable omnidirectional and angle-sensitive multichannel filters for the applications in optical filters based on PCs.

Tunable polychromatic filters based on semiconductor-superconductor-dielectric periodic and quasi-periodic hybrid photonic crystal

Abstract We theoretically report on the transmittance of a novel hybrid photonic crystals built from ternary periodic and quasi-periodic structures, each composed of dielectric (TiO2), semiconductor (GaAs) and high temperature superconductor (HgBa2Ca2Cu3O8+δ) materials. Using the transfer matrix method and the two-fluid model, two well-defined photonic gaps located in the infrared are accompanied by N resonant modes with high transmittance, where N depends on the number of aperiodic repetitions inserted within the periodic structure. We found that temperature, layer thicknesses, pressure, and incident angle all have strong and distinctive effects on the frequency of the gaps and resonant modes. By offering several tuning modalities and independent control over individual resonant frequencies, our hybrid photonic crystal provides outstanding flexibility for the design of terahertz polychromatic filters.

The influence of shape and orientation of scatters on the photonic band gap in two-dimensional Bravais-Moiré lattices

We perform a theoretical study of light propagation properties in two-dimensional square photonic crystals following Bravais-Moiré patterns, paying particular attention to the influence of the transversal shape and the orientation of the dielectric scatters onto the width and position of photonic band gaps. In this sense, we have considered both square and triangular transversal geometries for the dielectric scatters, together with the possible rotation of either all the elements or of one half of them, within the unit cell. Results for the photonic dispersion relations and band gaps are compared with those arising from the analysis of structures with simple bi-atomic Bravais unit cells. It comes out that wider photonic gaps appear when using square-shaped scatters. The use of Bravais-Moiré cells with the same kind of cores enhance the width of these gaps but shift them towards higher frequencies. Rotation of all elements within the cell in angles of 0.23 rad and 0.46 rad causes very small, if not null, changes in the photonic gap widths. However, the rotation of one half of the scatters in the cell, leaving the other half unrotated does produce noticeable modifications in the photonic band structure: For crystals made of square-shaped dielectric cores and simple cubic cells, this rotation strongly modifies the photonic structure, whilst for Bravais-Moiré crystals the same kind of change takes place for cells made of triangular-shaped cores.

Superconductor–semiconductor one-dimensional photonic crystal using a cancer cell as a defect layer

In this work, we calculate the transmittance spectrum for a one-dimensional photonic crystal composed by alternating superconductor and semiconductor layers. For these purposes, we shall consider the critical temperature of the superconductor that depends on the hydrostatic pressure, while the dielectric constant and layer thickness of the semiconductor depends on pressure. First, we insert a cavity with zero-cancer, Jurkat, and MCF-7 cells into the crystal. Then, using the transfer matrix method and the two-fluid model, we observed a defect mode within the photonic gap. The predominating response from the defect mode is mostly because of the hydrostatic pressure applied to the structure since confinement within the cavity is greater for zero-cancer cells, as determined by the quality factor. Herein, we may also observe that the defect mode shifts towards shorter frequencies as the layer thickness of the cavity increases for the crystal.

Transmittance spectrum within the THz range in one-dimensional Dodecanacci photonic crystals

In this work, we present a theoretical model to calculate the transmittance spectrum of a one-dimensional photonic crystal composed of polymer materials arranged based on a Dodecanacci sequence. In addition, in this crystal, we considered that the dielectric constants of these polymer materials depend on hydrostatic pressure. We calculated the transmittance spectrum in the THz range based on the transfer matrix method. Our numerical results reveal that the transmittance spectrum experiences a blueshift as the hydrostatic pressure increases. Our results also evidence the appearance of photonic gaps when the Dodecanacci sequence increases. Herein, the transmittance spectrum experiences a redshift upon increasing the thickness of the material layers. The results from this work can be applied to the design of narrowband filters.

Landau-Zener-Stückelberg interferometry in dissipative circuit quantum electrodynamics

We study Landau-Zener-St\"uckelberg (LZS) interferometry in a cQED architecture under the effects of dissipation. To be specific, we consider a superconducting qubit driven by a $\mathrm{dc}+\mathrm{ac}$ signal and coupled to a transmission line resonator, but our results are valid for general qubit-resonators devices. To take the environment into account, we assume that the resonator is coupled to an Ohmic quantum bath. The Floquet-Born-Markov master equation is numerically solved to obtain the dynamics of the system for an arbitrary amplitude of the drive and different timescales. We unveil important differences in the resonant patterns between the strong coupling and ultrastrong coupling regimes in the qubit-resonator interaction, which are mainly due to the magnitude of photonic gaps in the energy spectrum of the system. We identify in the LZS patterns the contribution of the qubit gap and the photonic gaps, showing that for large driving amplitudes the patterns present a weaving structure due to the combined intercrossing of the different gaps contributions.