Photonic Crystal Heterostructure Research Articles

Optical properties of cylindrical topological photonic crystal heterostructures

This paper uses a modified transfer matrix method to investigate the optical properties of a cylindrical topological photonic crystal heterostructure composed of two cylindrical photonic crystals. Topological photonic crystals are novel structures with topological edge states capable of field confinement and robust propagation. Numerical results showed that when the sum of the phases of the reflection coefficients of the two cylindrical photonic crystals is zero, a topological edge state occurs inside their overlapping band gaps. In the linear regime, the peak frequency of the topological edge states undergoes a redshift as the incidence angle increases. An increase in the incidence angle leads to a decrease (increase) in the Full width at half maximum of the E-polarized (H-polarized) topological edge states. As the incidence angle increases, the frequency separation between the E-polarized and H-polarized topological edge states increases, causing the cylindrical heterostructure to work as a polarizer. The performance of the cylindrical topological photonic crystal heterostructure as a polarizer is evaluated in the linear and nonlinear regimes. We showed that the peak frequency of the topological edge states undergoes a redshift irrespective of their polarization state as the intensity of the input light increases. We found that the structure has a good performance in the nonlinear regime due to the higher displacement in E-polarized topological edge states compared to H-polarized topological edge states. The findings of this paper might be beneficial in the construction of polarization-maintaining optical fiber, which has specific applications in telecommunications, fiber optic sensing, interferometry, and quantum key distribution.

Unidirectional self-imaging in multiple shifted photonic crystal interfaces.

In this study, we investigate the unidirectional self-imaging phenomenon in the shifted photonic crystal (PC) heterostructure. A spin-locked topological edge state, which originates from the mismatch of the Wannier center positions, can propagate along the shifted PC interface without backscattering. When the neighboring shifted PC interfaces are close enough, the coupling between the edge states happens, and coupled edge states (CES) can be found. Based on the finite element method (FEM) simulation, the spin-locked multimode interference (MMI) and self-imaging phenomenon of CES, including paired and symmetrical interference, are achieved in multiple shifted PC interfaces. To illustrate the application of the frequency splitters, the T-shaped and double cross-shaped structures with backscattering immunity and spin-locked characteristics are proposed. Our work provides an alternative way toward the design of a topological splitter by utilizing the photonic frequency and spin degrees of freedom at the same time.

Excitation/emission-enhanced heterostructure photonic crystal array synergizing with "DD-A" FRET entropy-driven circuit for high-resolution and ultrasensitive analysis of ctDNA

Circulating tumor DNA (ctDNA) is an emerging biomarker of liquid biopsy for cancer. But it remains a challenge to achieve simple, sensitive and specific detection of ctDNA because of low abundance and single-base mutation. In this work, an excitation/emission-enhanced heterostructure photonic crystal (PC) array synergizing with entropy-driven circuit (EDC) was developed for high-resolution and ultrasensitive analysis of ctDNA. The donor donor−acceptor FÖrster resonance energy transfer ("DD-A" FRET) was integrated in EDC based on the introduction of simple auxiliary strand, which exhibited higher sensitivity than that of traditional EDC. The heterostructure PC array was constructed with the bilayer periodic nanostructures of nanospheres. Because the heterostructure PC has the adjustable dual photonic band gaps (PBGs) by changing nanosphere sizes, and the "DD-A" FRET can offer the excitation and emission peak with enough distance, it helps the successful matches between the dual PBGs of heterostructure PC and the excitation/emission peaks of "DD-A" FRET; thus, the fluorescence from EDC can be enhanced effectively from both of excitation and emission processes on heterostructure PC array. Besides, high-resolution of single-base mutation was obtained through the strict recognition of EDC. Benefiting from the specific spectrum-matched and synergetic amplification of heterostructure PC and EDC with "DD-A" FRET, the proposed array obtained ultrasensitive detection of ctDNA with LOD of 12.9 fM, and achieved the analysis of mutation frequency as low as 0.01%. Therefore, the proposed strategy has the advantages of simple operation, mild conditions (enzyme-free and isothermal), high-sensitivity, high-resolution and high-throughput analysis, showing potential in bioassay and clinical application.

Rainbow Trapping with Engineered Topological Corner States and Cavities in Photonic Crystals

AbstractThis work presents a pioneering photonic crystal (PC) heterostructure design exploiting tailored topological corner states and cavities to unleash a fascinating topological rainbow effect. This effect arises from the strategic integration of a nontrivial topological PC with sharp corners within a trivial PC matrix, resulting in a heterostructure rich in corner states and cavities. The critical innovation lies in manipulating the sector angle of circular columns, granting dynamic control over the rainbow effect and light localization. This manipulation induces distinct group velocities for different light frequencies, leading to their separation and localization at specific corner states. This remarkable “rainbow trapping” phenomenon manifests as highly confined light exhibiting exceptional resilience against disorder. These findings illuminate a pathway toward crafting next‐generation photonic devices boasting unparalleled functionalities. The reconfigurable rainbow trapping holds immense potential for applications in wavelength division multiplexing, optical sensing, and even venturing into quantum information processing.

Wide-mode-area slow light waveguides in valley photonic crystal heterostructures

We designed slow-light waveguides with a wide mode area based on slab-type valley photonic crystal (VPhC) heterostructures which are composed of a graphene-like PhC sandwiched by two topologically distinct VPhCs. The group velocity of the topological guided mode hosted in a VPhC heterostructure can be slowed down by shifting the VPhC lattice toward the graphene-like PhC at the domain interfaces. Simultaneously, the mode width of the slow-light topological guided mode can be widened by increasing the size of the graphene-like PhC domain. We found that employing the graphene-like structure at the center domain is crucial for realizing a topological single-guided mode in such heterostructures. Furthermore, the impact of random fluctuations in air-hole size in the graphene-like domain was numerically investigated. Our simulation results demonstrate that the transmittance for the slow-light states can be kept high as far as the size fluctuation is small although it drops faster than that for fast-light states when the disorder level increases. The designed wide-mode-area slow-light waveguides are based on hole-based PhCs, offering novel on-chip applications of topological waveguides.

Angle-insensitive transmission and absorption with a PT phase transition via coupled interface states in hybrid one-dimensional photonic crystal heterostructures

Angle-insensitive transmission and absorption with a PT phase transition via coupled interface states in hybrid one-dimensional photonic crystal heterostructures

Peculiarities of Eu3+ Photoluminescence in Opal Photonic Crystal Films and Heterostructures Based of Them

Single opal films and heterostructures based on them grown by the method of vertically moving meniscus are characterized by the reflection spectroscopy technique and then impregnated with the Eu(CH3COO)3 × H2O salt. The suppression of the Eu3+ ion emission in single opal films is clearly detected within the photonic stop-band range. The weaker manifestation of this effect in heterostructures is more likely due to interface defects causing both the appearance of permitted states in the photonic stop band and the scattering of radiation in the direction of observation. With the further impregnation of opal films with glycerol to reduce the dielectric contrast from 1.85 to 1.13, the emission spectrum is mainly determined by the Eu3+ coordination environment effects accompanied with the broadening of bands and the spectral intensity redistribution.

Multi-band tunable strongly nonreciprocal thermal radiation in topological edge state coupled mode

Violating Kirchhoff's law of thermal radiation can break the reciprocity constraints on spectral emissivity and absorptivity, which provides new capabilities for managing photonic heat flow and fundamentally improves energy harvesting systems' efficiency. Currently, most micro-nano structures that violate Kirchhoff's law are mainly confined to single- or dual-band models, significantly limiting applications such as photonic energy conversion and thermal management. Here, a scheme is proposed for a topological one-dimensional photonic crystal heterostructure consisting of multiple photonic crystals and Weyl semimetals, and its absorptivity and emissivity are theoretically calculated by the transfer matrix method. The results show that the multi-band nonreciprocity that completely violates Kirchhoff's law can persist over broad angular and frequency ranges without requiring any external magnetic field via tuning the relevant parameters. Furthermore, the electric field distribution reveals that the formation of such multiple bands originates from the coupling between topological edge states, and the significant enhancement of the local field near the interface of the heterostructure provides favorable conditions for the realization of strong nonreciprocity. Our work may contribute to the design and development of multiband nonreciprocal devices for energy conversion and thermal management and may also provide design ideas for multiband reciprocal absorbers, filters, optical switching, etc.

Nonlinearly tunable Fano resonance in photonic crystal heterostructure with embedded a varactor-loaded split ring resonator

The study explores the Fano-type interference effect in a microstrip photonic crystal (PC) heterostructure integrated with a varactor-loaded split ring resonator (SRR), both experimentally and numerically. This effect capitalizes on the PC heterostructure’s ability to provide a broad continuous spectrum, while the embedded SRR offers a narrow discrete pathway. Through coherent interference between these elements, a sharp asymmetric Fano-type transmission spectrum emerges, accompanied by a notable group delay. Furthermore, the composite configuration exhibits an electric field enhancement at the Fano resonant frequency, enhancing the nonlinear sensitivity of the transmission spectrum. The nonlinear tunability of the Fano resonance is demonstrated by applying distinct input powers, allowing for the realization of a high-performance bistable electromagnetic switch and diode in the microwave regime. The proposed configuration exhibits key features such as significant transmission contrast, low threshold intensity, and relatively high transmission amplitude, all within a compact device volume, thanks to the Fano resonant mechanism in the PC heterostructure. This design paves the way for the implementation of active metamaterials-assisted components in micro- or nano-photonic circuits, with potential applications in advanced optical devices.

Optimizing slow light parameters in 2D-heterostructure photonic crystals with circular and square rods and holes

Theoretically, we aim to optimize the parameters related to slow light in a 2D heterostructure photonic crystal. Two types of heterostructures were investigated by joining two photonic crystals: one composed of square holes and the other with circular rods or vice versa. The plane wave expansion and supercell method are used to analyze the waveguide mode. Germanium is assumed to be the material for the rods and background. The group index and bandwidth for the waveguide appearing at the interface were optimized. A comprehensive survey of rod and hole size values reveals that the achieved group index bandwidth product of 0.72 is primarily due to the high bandwidth achieved within the optimized structure. Furthermore, our results confirm that rotating the square rods can further enhance slow light parameters, leading to a significantly higher group-index-bandwidth product than traditional semiconductor photonic crystal waveguides.

A dual-channel unidirectional filter of magneto-optical photonic heterostructure with a ring cavity

A dual-channel unidirectional filter of magneto-optical photonic crystal (MOPC) heterostructure with a ring cavity is proposed, based on topological edge states (TES). The ring cavity, which is composed of two MOPCs with opposite magnetic field, supports even and odd TESs. Finite element method (FEM) simulation results show that there are two perfect transmission peaks in drop port and dual-channel unidirectional filtering is achieved, which originates from cavity resonances of even and odd TESs. Furthermore, we investigate the influences of the cavity size, the magnetic field applied on MOPC, and the distance between the cavity and waveguide on dropping performance. A tunable dual-channel unidirectional filter with high Q factor up to 48000 can be achieved. Moreover, the proposed structure has strong robustness and can achieve immunity to various defects, including added PEC and the perturbation of the geometry parameter. Therefore, we obtain a waveguide-cavity structure based on MOPC heterostructure with the universality and efficient dropping performance, which provides the possibility for double-band one-way multiplexer and sensor.

Multichannel nonreciprocal thermal radiation with Weyl semimetal and photonic crystal heterostructure

A novel scheme for achieving multichannel nonreciprocal thermal radiation, which is in the form of a photonic crystal heterostructure sandwiched between two symmetric dielectric spacers and Weyl semimetal film backed with a metal film, is proposed and studied. A dual-channel nonreciprocal thermal emitter is first designed and studied as an illustration. It is found that near-perfect nonreciprocal radiations are realized at two different wavelengths at the same time. The underlying physical origin of this phenomenon is disclosed by investigating the magnetic field distribution. In addition, the novel dual-channel nonreciprocal radiation performance is robust to variations in geometric parameters, which will benefit real fabrication and application. What's more, the scheme can be easily expanded to achieve multi-band nonreciprocal radiation with the channel number larger than two by simply increasing the sequence order of the photonic crystal heterostructure. The scheme proposed in this paper provides a new possibility to develop novel multichannel nonreciprocal thermal emitters.

Strong coupling of multiple optical interface modes with ultra-narrow linewidth in one-dimensional topological photonic heterostructures.

Coherent coupling of optical modes with a high Q-factor underpins realization of efficient light-matter interaction with multi-channels in resonant nanostructures. Here we theoretically studied the strong longitudinal coupling of three topological photonic states (TPSs) in a one-dimensional topological photonic crystal heterostructure embedded with a graphene monolayer in the visible frequencies. It is found that the three TPSs can strongly interplay with one another in the longitudinal direction, enabling a large Rabi splitting (∼ 48 meV) in spectral response. The triple-band perfect absorption and selective longitudinal field confinement have been demonstrated, where the linewidth of hybrid modes can reach 0.2 nm with Q-factor up to 2.6 × 103. Mode hybridization of dual- and triple-TPSs were investigated by calculation of the field profiles and Hopfield coefficients of the hybrid modes. Moreover, simulation results further show that resonant frequencies of the three hybrid TPSs can be actively controlled by simply changing the incident angle or structural parameters, which are nearly polarization independent in this strong coupling system. With the multichannel, narrow-band light trapping and selectively strong field localization in this simple multilayer regime, one can envision new possibilities for developing the practical topological photonic devices for on-chip optical detection, sensing, filtering, and light-emitting.

Direct ink writing of three-dimensional Al2O3/polydimethylsiloxane photonic crystal heterostructures for terahertz frequencies

The photonic crystal heterostructures with multi-bandgap could manipulate multiple optical signals simultaneously, and have important applications in various multi-channel optical or optoelectronic devices. However, due to the limitations of materials and structure complexity, photonic crystal heterostructures for terahertz frequencies are rarely reported. Here, we report a facile and efficient approach to fabricate terahertz photonic crystal heterostructures (TPCHs) via direct ink writing (DIW) 3D printing technology. Al2O3/polydimethylsiloxane (PDMS) composite ink suitable for DIW has been developed. Al2O3/PDMS TPCHs with different structural parameters have been fabricated by DIW 3D printing. The results of simulation and experiments demonstrate that these TPCHs exhibit some special optical properties, such as bandgap deepening and dual-bandgap, compared with the conventional three-dimensional terahertz photonic crystals (3D-TPCs). The optical properties of TPCHs could be accurately regulated by varying the lattice constant of their compositional 3D-TPCs. The DIW 3D printing technology offers a new opportunity to create TPCHs with tailored photonic behavior for novel terahertz functional devices.

Angle-insensitive topological interface states in hybrid one-dimensional photonic crystal heterostructures containing all-dielectric metamaterials.

Topological interface states (TISs) in conventional one-dimensional (1D) photonic crystal (PhC) heterostructures strongly shift toward higher frequencies as the incident angle increases. This strong blueshift property of TISs intensively limits the operating angle ranges of TISs. Herein, we design two angle-insensitive photonic bandgaps (PBGs) in two hybrid 1D PhCs containing all-dielectric metamaterials. By cascading these two hybrid 1D PhCs to construct a hybrid 1D PhC heterostructure, we achieve an angle-insensitive TIS under transverse magnetic polarization. Empowered by the angle-insensitive property of the PBGs, the angular tolerance of the TIS reaches 69.65°, which is much higher than those of the TISs in conventional 1D PhC heterostructures. In addition, the angle-insensitive property of the TIS is robust against the layer thickness. Our work provides a viable route to achieving TISs with high angular tolerances and would facilitate the applications of photonic topological states.

Topologically protected multiple resonant modes in a one-dimensional photonic crystal heterostructure

This paper proposed and theoretically examined a double-interfaced one-dimensional photonic crystal heterostructure for strong localization of topologically protected resonant modes. It is challenging to achieve these modes for a range of wavelengths using a single photonic crystal. The design proposed in this study is a heterostructure of photonic crystals 1 (PC1) and 2 (PC2), and it provides distributed localized modes from the infrared to ultraviolet wavelength ranges. In addition, multiple resonant modes occur at certain photonic bandgaps due to the addition of the third photonic crystal (PC3), which is analytically modeled with the heterostructure of PC1 and PC2. The enhancement in the number of resonant modes depends on the PC2 number of unit-cells and the reflection phase of the proposed heterostructure. The reflection phase is abruptly changing from 0 to π for several wavelengths inside the bandgap. These resonance modes are also dependent on the topological behavior of each connected photonic crystal and are immune to small disorder and back-scattering within the crystal. The high-quality factor (Q-factor ∼107) shows strong light–matter interaction of these multiple resonant modes. The characterization was done in terms of the Zak phase, sign of the reflection phase, and bandgap overlapping. Consequently, this heterostructure may pave the way for new topological photonics and new applications in optoelectronics, frequency up-conversion, photonic devices, rainbow trapping, multiwavelength optical filters, and so on.

Visible and infrared dual-band anti-counterfeiting with self-assembled photonic heterostructures.

Self-assembled photonic structures have greatly expanded the paradigm of optical materials due to their ease of access, the richness of results offered and the strong interaction with light. Among them, photonic heterostructure shows unprecedent advances in exploring novel optical responses that only can be realized by interfaces or multiple components. In this work, we realize visible and infrared dual-band anti-counterfeiting using metamaterial (MM) - photonic crystal (PhC) heterostructures for the first time. Sedimentation of TiO2 nanoparticles in horizontal mode and polystyrene (PS) microspheres in vertical mode self-assembles a van der Waals interface, connecting TiO2 MM to PS PhC. Difference of characteristic length scales between two components support photonic bandgap engineering in the visible band, and creates a concrete interface at mid-infrared to prevent interference. Consequently, the encoded TiO2 MM is hidden by structurally colored PS PhC and visualized either by adding refractive index matching liquid or by thermal imaging. The well-defined compatibility of optical modes and facility in interface treatments further paves the way for multifunctional photonic heterostructures.

Large-area quantum-spin-Hall waveguide states in a three-layer topological photonic crystal heterostructure

Topological photonic edge states usually are formed at the interface between two domains of topologically trivial and nontrivial photonic crystals. The authors propose topological waveguide states with tunable widths in a three-layer topological photonic crystal heterostructure, which exhibit a helical pseudospin-momentum locking feature of the quantum spin Hall effect.

Perfect light absorber with a PT phase transition via coupled topological interface states

Recently, the concepts of parity–time (PT) symmetry and band topology have inspired many novel ideas for light manipulation in their respective directions. Here we propose and demonstrate a perfect light absorber with a PT phase transition via coupled topological interface states (TISs), which combines the two concepts in a one-dimensional photonic crystal heterostructure. By fine tuning the coupling between TISs, the PT phase transition is revealed by the evolution of absorption spectra in both ideal and non-ideal PT symmetry cases. Especially, in the ideal case, a perfect light absorber at an exceptional point with unidirectional invisibility is numerically obtained. In the non-ideal case, a perfect light absorber in a broken phase is experimentally realized, which verifies the possibility of tailoring non-Hermiticity by engineering the coupling. Our work paves the way for novel effects and functional devices from the exceptional point of coupled TISs, such as a unidirectional light absorber and exceptional-point sensor.

Tunable Fano resonance in coupled topological one-dimensional photonic crystal heterostructure and defective photonic crystal

In this paper, we theoretically investigate the transmission properties of a structure composed of a topological one-dimensional photonic crystal (1D PhC) heterostructure and a conventional 1D PhC containing indium-antimonide (InSb) as a defect layer using the transfer matrix method. The phenomenon of Fano resonance can be achieved by coupling the defect mode with the topological edge state mode, which is supported by the topological PhC. The numerical results show that a narrow Fano resonance is observed in the transmission spectrum of the structure in the presence of the external magnetic field applied to the InSb defect layer. The optical properties of the InSb defect layer, and, therefore, the Fano resonance, can be dynamically controlled by changing the applied external magnetic field. The results obtained with the proposed structure reveal that the magnetic field has the greatest influence on controlling the optical properties of the Fano resonance. These findings could be beneficial for optical devices such as optical filters, sensors, and optical switches.