Search Results (115)

In classic all-dielectric one-dimensional photonic crystals, transparent bands exhibit strong angular dispersion. Herein, we realize an angle-dispersion-free near-infrared transparent band in a one-dimensional photonic hypercrystal containing hyperbola-dispersion metamaterials. As the incident angle increases from 0° to 80°, the relative shifts of the wavelengths of four transmittance peaks within the transparent band are smaller than 1.5% and the bandwidth of the transparent band marginally fluctuates from 1098.2 to 1132.5 nm. Particularly, the angle-dispersion-free property of the transparent band is quite robust with respect to the layer thickness disturbance. Our work not only offers a viable method of achieving angle-dispersion-free transparent bands but also facilitates the development of transparency-based optical devices. Full article

Tunneling modes in all-dielectric one-dimensional photonic crystals can be utilized for multi-channel filtering. However, these tunneling modes generally blue shift upon increasing the incident angle. When hyperbolic metamaterials are introduced into one-dimensional photonic crystals, the competition between the propagation phase shifts in the dielectric materials and hyperbolic metamaterials can result in different angle dependencies, including blue shift, abnormal zero shift, and abnormal red shift. When the reduction in the propagation phase in the dielectric layer exceeds the increment in the propagation phase in the hyperbolic metamaterial, the tunneling modes are blue-shifted; conversely, when the phase increment in the hyperbolic metamaterial exceeds the phase reduction in the dielectric layer, the tunneling modes are abnormally red-shifted. When the phase changes in the two materials are the same, the tunneling modes are angle independent. In this study, we investigated the multiple filtering effects of one-dimensional photonic structures composed of hyperbolic metamaterials. These composed structures exhibited multiple tunneling modes based on one-, two-, or three-angle dependencies and can be applied in novel optical devices with different angle-dependence requirements. Full article

In this paper, we propose an innovative approach based on the wavelength optimization of a light source for a simple, high-performance surface plasmon resonance (SPR) sensor utilizing comprehensive reflectance analysis in the angular domain. The proposed structure consists of a glass substrate, an adhesion layer of titanium dioxide, a silver plasmonic layer, and a 2D material. Analysis is performed in the Kretschmann configuration for liquid analyte sensing. Sensing parameters such as the refractive index (RI) sensitivity, the reflectance minimum, and the figure of merit (FOM) are investigated in the first step of this study as a function of the thickness of the silver layer together with the RI of a coupling prism. Next, utilizing the results offering a fused silica prism, the thickness of the silver layer and the wavelength of the light source are optimized for the structure with the addition of a 2D material, black phosphorus (BP), which is studied along different principal directions, the zigzag and armchair directions. In addition, a new approach of adjusting the source wavelength using a one-dimensional photonic crystal combined with an LED, is presented. Based on this analysis, for the reference structure at a wavelength of 632.8 nm, the optimized silver layer thickness is 50 nm, and the achieved RI sensitivity ranges from 193.9 to 251.5 degrees per RI unit (deg/RIU), with the highest FOM reaching 52.3 RIU⁻¹. In addition, for the modified structure with BP, the achieved RI sensitivity varies in the range of 269.1–351.2 deg/RIU at the optimized wavelength of 628 nm, with the highest FOM reaching 44.7 RIU⁻¹ for the zigzag direction. Due to the optimization and adjusting the wavelength of the source, the results obtained for the proposed SPR structure could have significant implications for the development of more sensitive and efficient sensors employing a simple plasmonic structure. Full article

Recent advances in topological photonics provide unprecedented opportunities to realize a photonic cavity. A recent work shows that the electromagnetic wave can be effectively trapped via the shifted photonic crystal interfaces (SPCIs), which offers an alternative approach to realizing the photonic cavity. Here, we proposed one-dimensional topological insulators based on an SPCIs-induced cavity chain, which is analogous to the Su–Schrieffer–Hegger model and is compatible with the silicon-on-insulator platform. Owing to the asymmetry feature of SPCIs-induced cavities, the topological cavity chains can be either realized by alternating the cavity modes or by tuning the distance between two cavities. The nontrivial band topology of SPCIs-induced cavity chains is further confirmed by observing topological end states, which exhibit robustness against geometrical imperfections. Our work holds promises for designing robust photonic devices, which may find potential applications in future integrated photonics. Full article

Terahertz (THz) molecular fingerprint spectroscopy provides a powerful label-free tool for detecting trace-amount analytes. Introducing extra microstructures such as metasurfaces to confine the field energy is essential to improve the sensitivity. However, the area of analyte film on conventional enhancing metasurfaces must be larger than the beam spot in a free-space measuring setup. Here, we propose a tunable defect cavity of one-dimensional photonic crystal in the combined coaxial waveguide (CCW) and enhance the broadband THz fingerprint of trace analytes on a much smaller area. The peaks of high Q resonances can form a wide absorption spectrum by changing the length of the rubber part of the coaxial waveguide. For the 0.2 µm α-lactose film sample in the frequency range of 0.48–0.58 THz, the absorption enhancement factor of 89.2 times based on the thickness can be achieved and the sample area is about 1/1700 of that in the free-space measurement with the 5 mm beam waist. We first introduce the coaxial waveguide in the terahertz absorption spectra enhancement. With our proposed structure the analyte volume is effectively reduced which is significant in the real application scenario. Full article

We propose two types of structures to achieve the control of Fano and electromagnetically induced transparency (EIT) line shapes, in which dual one-dimensional (1D) photonic crystal nanobeam cavities (PCNCs) are side-coupled to a bus waveguide with different gaps. For the proposed type Ⅰ and type Ⅱ systems, the phase differences between the nanobeam periodic structures of the two cavities are π and 0, respectively. The whole structures are theoretically analyzed via the coupled mode theory and numerically demonstrated using the three-dimensional finite-difference time-domain (3D FDTD) method. The simulation results show that the proposed structure can achieve several kinds of spectra, including Fano, EIT and asymmetric EIT line shapes, which is dependent on the width of the bus waveguide. Compared to the previously proposed Fano resonator with 1D PCNCs, the proposed structures have the advantages of high transmission at the resonant peak, low insertion loss at non-resonant wavelengths, a wide free spectral range (FSR) and a high roll-off rate. Therefore, we believe the proposed structure can find broad applications in optical switches, modulators and sensors. Full article

Semitransparent organic solar cells (ST-OSCs) have garnered more interest and stand out as promising candidates for next-generation solar energy harvesters with their unique advantages. However, challenges remain for the advancement of colorful ST-OSCs, such as enhancing the light absorption and transmittance without considerable power conversion efficiency (PCE) losses. Herein, an optical analysis of silver (Ag) electrodes and one-dimensional photonic crystals (1DPCs) was conducted by simulations, revealing the presence of optical Tamm states (OTSs) at the interface of Ag/1DPCs. Furthermore, the spectral and electrical properties were fine-tuned by modulating the OTSs through theoretical simulations, utilizing PM6:Y6 as the active layer. The structural parameters of the ST-OSCs were optimized, including the Ag layer thickness, the central wavelength of 1DPCs, the first WO₃ layer thickness, and the pair number of WO₃/LiF. The optimization resulted in the successful development of blue, violet-blue, and red ST-OSC devices, which exhibited transmittance peak intensities ranging from 31.5% to 37.9% and PCE losses between 1.5% and 5.2%. Notably, the blue device exhibited a peak intensity of 37.0% and a PCE of 15.24%, with only a 1.5% loss in efficiency. This research presents an innovative approach to enhancing the performance of ST-OSCs, achieving a balance between high transparency and high efficiency. Full article

In this study, we demonstrate the reflectance spectrum of one-dimensional photonic crystals comprising two different types of metamaterials. In this regard, the designed structure can act as a simple and efficient detector for fat concentrations in milk samples. Here, the hyperbolic and gyroidal metamaterials represent the two types of metamaterials that are stacked together to construct the candidate structure; meanwhile, the designed 1D PCs can be simply configured as [G(ED)^m]^S. Here, G refers to the gyroidal metamaterial layers in which Ag is designed in a gyroidal configuration form inside a hosting medium of TiO₂. In contrast, (ED) defines a single unit cell of the hyperbolic metamaterials in which two layers of porous SiC (E) and Ag (D) are combined together. It is worth noting that our theoretical and simulation methodology is essentially based on the effective medium theory, characteristic matrix method, Drude model, Bruggeman’s approximation, and Sellmeier formula. Accordingly, the numerical findings demonstrate the emergence of three resonant peaks at a specified wavelength between 0.8 μm and 3.5 μm. In this context, the first peak located at 1.025 μm represents the optimal one regarding the detection of fat concentrations in milk samples due to its low reflectivity and narrow full bandwidth. Accordingly, the candidate detector could provide a relatively high sensitivity of 3864 nm/RIU based on the optimal values of the different parameters. Finally, we believe that the proposed sensor may be more efficient compared to other counterparts in monitoring different concentrations of liquid, similar to fats in milk. Full article

Optical absorbers based on Tamm plasmon states are known for their simple structure and high operational efficiency. However, these absorbers often have limited absorption channels, and it is challenging to continuously adjust their light absorption rates. Here, we propose a Tamm plasmon state optical absorber composed of a layered stack structure consisting of one-dimensional topological photonic crystals and graphene nano-composite materials. Using the four-by-four transfer matrix method, we investigate the structural relationship of the absorber. Our results reveal that topological interface states (TISs) effectively excite the optical Tamm state (OTS), leading to multiple absorption peaks. This expands the number of absorption channels, with the coupling number of the TIS determining the transmission quality of these channels—a value further adjustable by the period number of the photonic crystals. Tuning the filling factor, refractive index, and thickness of the graphene nano-composite material allows for a wide range of control over the device’s absorption rate, from 0 to 1. Additionally, adjusting the defect layer thickness, incident angle, and Fermi energy enables us to control the absorber’s operational bandwidth and the switching of its absorption effect. This work presents a new approach to expanding the tunability of optoelectronic devices. Full article

Polymer-stabilized cholesteric liquid crystals (PSCLCs) have emerged as promising candidates for one-dimensional photonic lattices that enable precise tuning of the photonic band gap (PBG). This work systematically investigates the effect of polymer concentrations on the AC electric field-induced tuning of the PBG in PSCLCs, in so doing it explores a range of concentrations and provides new insights into how polymer concentration affects both the stabilization of cholesteric textures and the electro-optic response. We demonstrate that low polymer concentrations (≈3 wt. %) cause a blue shift in the short wavelength band edge, while high concentrations (≈10 wt. %) lead to a contraction and deterioration of the reflection band. Polarization optical microscopy was conducted to confirm the phase transition induced by the application of an electric field. The observations confirm that increased polymer concentration stabilizes the cholesteric texture. Particularly, the highly desired fingerprint texture was stabilized in a sample with 10 wt. % of the polymer, whereas it was unstable for lower polymer concentrations. Additionally, higher polymer concentrations also improved the dissymmetry factor and stability of the lasing emission, with the dissymmetry factor reaching the value of around 2 for samples with 10 wt. % of polymer additive. Our results provide valuable comprehension into the design of advanced PSCLC structures with tunable optical properties, enhancing device performance and paving the way for innovative photonic applications. Full article

We study the nested topological band-gap structure of one-dimensional (1D) photonic super-lattices. One cell of the super-lattice is composed of two kinds of photonic crystals (PhCs) with different topologies so that there is a domain wall (DW) state at the interface between the two PhCs. We find that the coupling of periodic DWs could form a new band-gap structure inside the original gap. The new band-gap structure could be topologically nontrivial, and a topological phase transition can occur if the structural or material parameters of the PhCs are tuned. Theoretically, we prove that the Hamiltonian of such coupled DWs can be reduced to the simple Su–Schrieffer–Heeger (SSH) model. Then, if two super-lattices carrying different topological phases are attached, a new topological interface state can occur at the interface between the two super-lattices. Finally, we find the nested topological band-gap structure in two-dimensional (2D) photonic super-lattices. Consequently, such nested topological structures can widely exist in complex super-lattices. Our work improves the topological study of photonic super-lattices and provides a new way to realize topological interface states and topological phase transitions in 1D and 2D photonic super-lattices. Topological interface states in super-lattices are sensitive to frequency and have high accuracy, which is desired for high-performance filters and high-finesse cavities. Full article

In this paper, we study the nonlinear optical bistability (OB) in a symmetrical multilayer structure. This multilayer structure is constructed by embedding a nonlinear three-dimensional Dirac semimetal (3D DSM) into a Fabry–Perot cavity composed of one-dimensional photonic crystals. The OB phenomenon stems from the third order nonlinear conductivity of 3D DSM. The local field of resonance mode could enhance the nonlinearity and reduce the thresholds of OB. This structure achieves the tunability of OB due to the fact that the transmittance could be modulated by the Fermi energy. It is found that the OB threshold and threshold width could be remarkably reduced by increasing the Fermi energy of the 3D DSM. Besides, we also found that the OB curve depends heavily on the angle of incidence of the incident light, the structural parameters of the Fabry–Perot cavity, and the position of the 3D DSM inside the cavity. After parameter optimization, we obtained OB with a threshold of ${10}^6 \mathrm{V}/\mathrm{m}$. We believe this simple multilayer structure could provide a reference idea for realizing low-threshold and tunable all-optical switching devices. Full article

Responsive photonic crystal hydrogel sensors are renowned for their colorimetric sensing ability and can be utilized in many fields such as medical diagnosis, environmental detection, food safety, and industrial production. Previously, our group invented responsive photonic nanochains (RPNCs), which improve the response speed of photonic crystal hydrogel sensors by at least 2 to 3 orders of magnitude. However, RPNCs are dispersed in a liquid medium, which needs a magnetic field to orient them for the generation of structural colors. In addition, during repeated use, the process of cleaning and redispersing can cause entanglement, breakage, and a loss of RPNCs, resulting in poor stability. Moreover, when mixing with the samples in liquid, the RPNCs may lead to the contamination of the samples being tested. In this paper, we incorporate one-dimensional oriented RPNCs with agarose gel film to prepare heterogeneous hydrogel films. Thanks to the non-responsive and porous nature of the agarose gel, the protons diffuse freely in the gel, which facilitates the fast response of the RPNCs. Furthermore, the “frozen” RPNCs in agarose gel not only enable the display of structural colors without the need for a magnet but also improve the cycling stability and long-term durability of the sensor, and will not contaminate the samples. This work paves the way for the application of photonic crystal sensors. Full article

The combination of higher-order topological insulators and valley photonic crystals has recently aroused extensive attentions due to the great potential in flexible and efficient optical field manipulations. Here, we computationally propose a photonic device for the 1550 nm communication band, in which the topologically protected electromagnetic modes with high quality can be selectively triggered and modulated on demand. Through introducing two valley photonic crystal units without any structural alteration, we successfully achieve multi-dimensional coupled topological states thanks to the diverse electromagnetic characteristics of two valley edge states. According to the simulations, the constructed topological photonic devices can realize Fano lines on the spectrum and show high-quality localized modes by tuning the coupling strength between the zero-dimensional valley corner states and the one-dimensional valley edge states. Furthermore, we extend the valley-locked properties of edge states to higher-order valley topological insulators, where the selected corner states can be directionally excited by chiral source. More interestingly, we find that the modulation of multi-dimensional coupled photonic topological states with pseudospin dependence become more efficient compared with those uncoupled modes. This work presents a valuable approach for multi-dimensional optical field manipulation, which may support potential applications in on-chip integrated nanophotonic devices. Full article

Topological photonics has been widely investigated due to its profound physical significance and great number of potential applications. Microwaves have long wavelengths, so it is relatively easy to manufacture large-sized microwave photonic crystals, enabling researchers to observe and measure phenomena such as topological boundary states. Nevertheless, the quality factors (QFs) of most resonators composed of traditional materials in the microwave region are relatively low, leading to topological edge states with high decay rates. In this study, we present a one-dimensional topological photonic crystal in the microwave region based on coupled superconducting resonators. A topological state with a QF as high as 6000 is observed, which proves this to be a new platform for the investigation of topological photonics with low decay rates in the microwave regime. Full article