Photonic Band Structure Research Articles

Electric field distribution of photonic crystals waveguide with function line defect

In this work, the finite element and supercell methods are used to study the effect of function line defect on the photonic band structure and electric field distribution in a two-dimensional photonic crystals waveguide. We designed to introduce a row of function defect in the photonic crystals waveguide. The transmission characteristics of the photonic crystals waveguides are modulated by adjusting the function coefficient k and parameter b of the dielectric constant of the function defect dielectric column. By changing the structure parameters of the dielectric constant, the radius of the function defect dielectric column and the dielectric constant of the two-dimensional regular photonic crystals dielectric column material, we found that the band gap position, band gap width, defect mode number, defect mode position and defect mode width change. The electric field is well localized at the defect location, but their intensity are different. The three-pole defect mode can be activated, and the defective mode eigenfield distribution is symmetrical. Compared with the two-dimensional regular photonic crystals waveguide, the width of forbidden band becomes wider and the number of defect modes increases. The band gap structure and electric field distribution have the adjustability for the two-dimensional photonic crystals waveguide with function line defect. These results will provide new designed methods and theoretical basis for the related optical devices.

Discussion on fabrication accuracy of infrared topological photonic structures using hyperspectral Fourier image spectroscopy

Compared to conventional periodic nanostructures such as photonic crystals, topological photonic systems require more precise fabrication techniques due to the need to place multiple dielectrics at appropriate positions within a unit cell, and this becomes particularly remarkable in the optical communication band. In this paper, observing photonic band structures by using hyperspectral Fourier image spectroscopy, we quantitatively discuss the fabrication accuracy of typical topological photonic systems in which triangle nanoholes were arranged in a deformed honeycomb lattice with C 6 v symmetry. Here the size and corner radius of triangle nanoholes were precisely controlled using shape correction electron beam lithography. The results showed that the fabrication error must be controlled to below ∼ 10 n m for the size and ∼ 30 n m for the corner radius, in order to achieve the desired topological edge state that occurs at the interface between two photonic structures different in topology.

Magic configurations in moiré superlattice of bilayer photonic crystals: Almost-perfect flatbands and unconventional localization

We investigate the physics of photonic band structures of the moir\'e patterns that emerged when overlapping two uni-dimensional (1D) photonic crystal slabs with mismatched periods. The band structure of our system is a result of the interplay between intra-layer and inter-layer coupling mechanisms, which can be fine-tuned via the distance separating the two layers. We derive an effective Hamiltonian that captures the essential physics of the system and reproduces all numerical simulations of electromagnetic solutions with high accuracy. Most interestingly, \textit{magic distances} corresponding to the emergence of photonic flatbands within the whole Brillouin zone of the moir\'e superlattice are observed. We demonstrate that these flatband modes are tightly localized within a moir\'e period. Moreover, we suggest a single-band tight-binding model that describes the moir\'e minibands, of which the tunnelling rate can be continuously tuned via the inter-layer strength. Our results show that the band structure of bilayer photonic moir\'e can be engineered in the same fashion as the electronic/excitonic counterparts. It would pave the way to study many-body physics at photonic moir\'e flatbands and novel optoelectronic devices.

Strategical Deep Learning for Photonic Bound States in the Continuum

AbstractResonance is instrumental in modern optics and photonics. While one can use numerical simulations to sweep geometric and material parameters of optical structures, these simulations usually require considerably long calculation time and substantial computational resources. Such requirements significantly limit their applicability in the inverse design of structures with desired resonances. The recent introduction of artificial intelligence allows for faster spectra predictions of resonance. However, even with relatively large training datasets, current end‐to‐end deep learning approaches generally fail to predict resonances with high‐quality‐factors (Q‐factor) due to their intrinsic non‐linearity and complexity. Here, a resonance informed deep learning (RIDL) strategy for rapid and accurate prediction of the optical response for ultra‐high‐Q‐factor resonances is introduced. By incorporating the resonance information into the deep learning algorithm, the RIDL strategy achieves a high‐accuracy prediction of reflection spectra and photonic band structures while using a comparatively small training dataset. Further, the RIDL strategy to develop an inverse design algorithm for designing a bound state in the continuum (BIC) with infinite Q‐factor is applied. The predicted and measured angle‐resolved band structures of this device show minimal differences. The RIDL strategy is expected to be applied to many other physical phenomena such as Gaussian and Lorentzian resonances.

Photonic crystal analysis for multiplexer and de-multiplexer applications

In our present work, we have made an investigation of several theoretical tools using the finite element method depending on the COMSOL MULTIPHYSICS program, for intuitive insight into the optical properties of the optical crystal. Analysis of the bandgap of a two-dimensional periodic photonic crystal with square lattice, evaluate the photonic band structure by the eigenfrequency of the unit cell of the first Brillouin zone. Moreover, creating defect mode inside the bandgap of photonic crystal, such as a resonant cavity, waveguide defect, narrowband filter, sharp drop filter, channel drop filter, waveguide bends, waveguide splitter promises us to a platform to design devices that includes a certain optical range of wavelengths. The transmission, as a result, the influence of the light localized in the defect area of the periodic structure of the photonic crystal. This study is important for producing photonic integrated circuits based on photonic crystals for future advanced optical communication.

Ultra-fast tunable optoelectronic full-adder based on photonic crystal ring resonators covered by graphene nanoshells

This paper reports a novel design of a tunable optoelectronic full-adder using two photonic crystal ring resonators (PCRRs). Every PCRR consists of a matrix of silicon rods surrounded by silica rods coated with graphene nanoshells (GNSs). The proposed full-adder is formed by three input ports, two PCRRs, and two output ports for ‘SUM’ and ‘CARRY’. The plane wave expansion technique is used to study the photonic band structure of the fundamental photonic crystal (PhC) microstructure, and the finite-difference time-domain method is also employed in the final design for solving Maxwell's equations to analyze the light propagation inside the structure. We can tune the PhC resonant mode for our desired application by setting the chemical potential of GNSs with an appropriate gate voltage. The numerical results reveal that when the chemical potential of GNSs changes, the switching mechanism occurs and manages the coupling and propagation direction of the input beam inside the structure. We systematically study the effects of physical parameters on the transmission, reflection, and absorption spectra . Our numerical results also demonstrate that the maximum delay is about 0.8 ps. The 663 μm 2 area of the proposed full-adder based on two-dimensional materials makes it a building block of every photonic integrated circuit used for data processing systems. • A fast and compact all-optical full-adder using photonic crystal ring resonators (PCRRs). • A maximum steady-state time of about 0.8 ps and the structure's total size of 663 μm 2 . • There is no need to increase the input intensity for the appearance of the nonlinear effect. • The ON-OFF contrast ratios for Sum and Carry are 16 dB and 14 dB, respectively. • The full-adder is applicable in optical integrated circuits for high-speed signal processing.

Surface-plasmon-like distributions in metallic square shield array

In this work, we present the numerical study of 2D photonic crystals (PCs) made of square metallic shields distributed in a square arrangement embedded in air for the transversal electric (TE) polarization in the Γ - X direction. It is presented the modification of the photonic band structure (PBS), which shows the redistribution of bands with low dispersion at lower and higher frequencies around the surface plasmon frequency (SPF) with the decrease in the width of the shield walls. Considering the distributions of |Hz|2 and |E|2 in the unit cell, it is observed high intensity values in the metallic region, even for low frequencies, with a distribution like surfaces plasmons, due to the interaction of the electromagnetic modes located at the inner and the exterior surfaces of the shield. Also, it is observed that the electric field is strongly localized in the inner hole of the shield at low frequencies, which is quite different from the conventional rod geometry. These results would be utilized in electric field confinement for technological applications.

High-power CW oscillation of 1.3-µm wavelength InP-based photonic-crystal surface-emitting lasers.

We demonstrate high-power continuous-wave (CW) lasing oscillation of 1.3-µm wavelength InP-based photonic-crystal surface-emitting lasers (PCSELs). Single-mode operation with an output power of over 100 mW, a side-mode suppression ratio (SMSR) of over 50 dB, and a narrow single-lobe beam with a divergence angle of below 1.2° are successfully achieved by using a double-lattice photonic crystal structure consisting of high-aspect-ratio deep air holes. The double lattice is designed to enhance both the in-plane optical feedback and the surface radiation effects in the photonic crystal. The coupling coefficients for 180 ∘, +90 ∘, and -90 ∘ diffractions are estimated from the measurements of the photonic band structure as κ1D = 417 cm-1, κ2D+ = 135 cm-1, and κ2D- = 65 cm-1, respectively. The stable single-mode, high-beam-quality operation is attributed to these large coupling coefficients introduced by the asymmetric double-lattice structure.

Photonic Type-III Nodal Loop and Topological Phase Transitions at Bilayer Metasurfaces

In momentum space, the nodal loop is regarded as a ring-shaped band degeneracy and is classified into type-I and type-II configurations depending on the positive/negative dispersions of the degenerating bands. Here, we experimentally observe a new class of nodal loop in the photonic band structure, employing an artificially designed bilayer metasurface. Such degeneracy, termed type-III nodal loop, is formed by the crossing between a resonant flat band and a positively dispersive band and is protected by mirror symmetry Mz, which manifests in the metasurface’s bilayer architecture. Furthermore, the sequential topological transitions of band degeneracy from the nodal loop via Dirac point to gapped phase are demonstrated at the metasurfaces. Such transitions are enabled by the bilayer design and end with a pair of edge states on the domain wall of gapped systems. Our work reveals that properly engineered bilayer metasurfaces offer rich physics and vast flexibility in two-dimensional topological photonic research through assembling and tunning more symmetries and degrees of freedom along the stacking direction.

Photonic band structure behavior in a lattice with a star defect

In this work, we calculate the photonic band structure for a defective two-dimensional photonic crystal with a star defect using the plane wave expansion method and supercell technique. The photonic crystal is composed of triangular scatterers distributed in a honeycomb lattice with an air background. For transverse magnetic polarization, a defect mode was identified in the photonic band gap with the same intensity of the electrical displacement concentrated within the triangles. By calculating the gap map based on triangle lengths, the defect mode is concentrated within the photonic band gap for triangles with lengths of L = 0.48a, wherein a represents the lattice constant. When considering scatterer rotation in the lattice, the photonic band gap is maximized for rotations of θ=π/6, which generates the presence of two defect modes for transverse electric polarization. Finally, regarding the dependence of the refractive index on the applied pressure, the defect mode is tuned at lower frequencies as pressure increases from 0 to 6 GPa.

Nonreciprocal Single-Photon Band Structure.

We study a single-photon band structure in a one-dimensional coupled-resonator optical waveguide that chirally couples to an array of two-level quantum emitters (QEs). The chiral interaction between the resonator mode and the QE can break the time-reversal symmetry without the magneto-optical effect and an external or synthetic magnetic field. As a result, nonreciprocal single-photon edge states, band gaps, and flat bands appear. By using such a chiral QE coupled-resonator optical waveguide system, including a finite number of unit cells and working in the nonreciprocal band gap, we achieve frequency-multiplexed single-photon circulators with high fidelity and low insertion loss. The chiral QE-light interaction can also protect one-way propagation of single photons against backscattering. Our work opens a new door for studying unconventional photonic band structures without electronic counterparts in condensed matter and exploring its applications in the quantum regime.

Analytically Supported Hybrid Photonic–plasmonic Crystal Design Using Artificial Neural Networks

An analytical and numerical study of hybrid photonic–plasmonic crystals is presented. The proposed theoretical model describes a system composed of a dielectric photonic crystal on a metallic thin film. To show the validity and usefulness of the model, four particular structures are analyzed: a one-dimensional crystal and three lattices of two-dimensional crystals. The model can calculate the photonic band structure of photonic–plasmonic crystals as a function of structural characteristics, showing two partial bandgaps for a square lattice, and complete bandgaps for triangular lattices. Furthermore, using a particular high-symmetry path, a full bandgap emerges in rectangular lattices, even with a small refractive index contrast. Using the analytical model, a dataset is generated to train an artificial neural network to predict the center and width of the bandgap, that is, the forward design. In addition, an artificial neural network is trained to tune the optical response, that is, to perform the inverse design. The analytical results are consistent with the physics of the system studied and are supported by numerical simulations. Moreover, the prediction accuracy of the artificial neural networks is better than 95%. Overall, this paper reports a useful tool for tuning the optical properties of hybrid photonic–plasmonic crystals with potential applications in waveguides, nanocavities, mirrors, etc.

High-speed infrared photonic band microscope using hyperspectral Fourier image spectroscopy.

In this study, we developed a photonic band microscope based on hyperspectral Fourier image spectroscopy. The developed device constructs an infrared photonic band structure from Fourier images for various wavelength obtained by hyperspectral imaging, which make it possible to speedily measure the dispersion characteristics of photonic nanostructures. By applying the developed device to typical photonic crystals and topological photonic crystals, we succeeded in obtaining band structures in good agreement with the theoretical prediction calculated by the finite element method. This device facilitates the evaluation of physical properties in various photonic nanostructures, and is expected to further promote related fields.

Topological transitions and Anderson localization of light in disordered atomic arrays

We explore the interplay of disorder and topological phenomena in honeycomb lattices of atoms coupled by the electromagnetic field. On the one hand, disorder can trigger transitions between distinct topological phases and drive the lattice into the topological Anderson insulator state. On the other hand, the nontrivial topology of the photonic band structure suppresses Anderson localization of modes that disorder introduces inside the band gap of the ideal lattice. Furthermore, we discover that disorder can both open a topological pseudogap in the spectrum of an otherwise topologically trivial system and introduce spatially localized modes inside it.

Analysis of Photonic Band Structure Tunability for TE and TM Modes in a Silicon and Polymer Based Ternary Photonic Crystal for Visible Range Devices

Analysis of Photonic Band Structure Tunability for TE and TM Modes in a Silicon and Polymer Based Ternary Photonic Crystal for Visible Range Devices

Wavelength selection in focusing non-uniform grating couplers: A coupling efficiency curve asymmetry and bandwidth analysis

We report a combined experimental and computational investigation of the multi-wavelength response of a series of focusing non-uniform grating couplers designed on multiple SOI thicknesses interfaced with two different fiber coupling schemes. In particular, we demonstrate either the existence of an asymmetry of the coupling efficiency curve shape, with respect to the tuning wavelength (1550 nm), related to the metastructure features, and how the photonic band structure of such metastructures can be calculated and exploited to evaluate their multi-wavelength response, in terms of multi-BW analysis. These results can be a positive stimulus for a further comprehension of the electromagnetic response of non-uniform grating couplers, particularly interesting as a valid option for integrated photonics applications.

In-plane resonant excitation of quantum dots in a dual-mode photonic-crystal waveguide with high β-factor

A high-quality quantum dot (QD) single-photon source is a key resource for quantum information processing. Exciting a QD emitter resonantly can greatly suppress decoherence processes and lead to highly indistinguishable single-photon generation. It has, however, remained a challenge to implement strict resonant excitation in a stable and scalable way, without compromising any of the key specs of the source (efficiency, purity, and indistinguishability). In this work, we propose a novel dual-mode photonic-crystal waveguide that realizes direct in-plane resonant excitation of the embedded QDs. The device relies on a two-mode waveguide design, which allows exploiting one mode for excitation of the QD and the other mode for collecting the emitted single photons with high efficiency. By proper engineering of the photonic bandstructure, we propose a design with single-photon collection efficiency of β > 0.95 together with a single-photon impurity of ϵ < 5 × 10−3 over a broad spectral and spatial range. The device has a compact footprint of and would enable stable and scalable excitation of multiple emitters for multi-photon quantum applications.

Optical excitations of Skyrmions, knotted solitons, and defects in atoms

Analogies between non-trivial topologies of matter and light have inspired numerous studies, including defect formation in structured light and topological photonic band structures. Three-dimensional topological objects of localised particle-like nature attract broad interest across discipline boundaries from elementary particle physics and cosmology to condensed matter physics. Here we propose how simple structured light beams can be transformed into optical excitations of atoms with considerably more complex topologies representing three-dimensional particle-like Skyrmions. This construction can also be described in terms of linked Hopf maps, analogous to knotted solitons of the Skyrme-Faddeev model. We identify the transverse polarisation density current as the effective magnetic gauge potential for the Chern-Simons helicity term. While we prepare simpler two-dimensional baby-Skyrmions and singular defects using the traditional Stokes vectors on the Poincaré sphere for light, particle-like topologies can only be achieved in the full optical hypersphere description that no longer discards the variation of the total electromagnetic phase of vibration.

Stacked chalcogenide metasurfaces for third harmonic generation in the UV range

We show that an appropriately designed chalcogenide metasurface allows the enhancement of harmonic generation in the UV range, a regime that conventional wisdom deems inaccessible because of absorption. Here we exploit a combination of the photonic band structure that forms when stacking As2S3 metasurfaces, phase-locking, nonlinear dispersion, and improved field localization to enhance third harmonic conversion efficiency. We demonstrate an improvement of two orders of magnitude with respect to the single layer counterpart notwithstanding the fact that the harmonic signal is tuned deep in the absorption range at 285 nm.

Broadband wavelength tuning of electrically stretchable chiral photonic gel

Abstract Chiral photonic-band structure provides technical benefits in the form of a self-assembled helical structure and further functional wavelength tunability that exploits helical deformation according to pitch changes. The stopband wavelength control of the chiral photonic-band structure can be obtained by individual electrical methods or mechanical stretching deformation approaches. However, research on combined electric control of stretchable chiral photonic-band wavelength control while ensuring optical stability during the tuning process has remained limited till now. In this study, using the hybrid structure of elastomeric mesogenic chiral photonic gels (CPGs) with an electrically controlled dielectric soft actuator, we report the first observation of electrically stretchable CPGs and their electro-mechano-optical behaviors. The reliable wavelength tuning of a CPG to a broadband wavelength of ∼171 nm changed with high optical stability and repeated wavelength transitions of up to 100 times. Accordingly, for the first time, electrical wavelength tuning method of stretchable chiral liquid crystal photonicband structure was investigated.