Fabrication of AAO-based 3D particle-in-cavity nanostructures for ultrasensitive SERS detection.

Testing the Starobinsky model of inflation with resonant cavities

Abstract In this paper, a millimeter-wave dual-band filter with a W-band operating frequency is proposed based on a multi-mode resonator. Based on the research of multimode resonators, an ultra-wideband filter and a filter with transmission zeros are designed. By cascading and optimizing, a dual-band pass filter working in the W-band is designed. The two operating bands are 84.96 GHz ∼ 89.33 GHz and 96.57 GHz ∼ 103.64 GHz, respectively, and the 3 dB fractional bandwidth is 5% and 7.1%, respectively. The designed structure is prepared by using the CNC process. After testing, the test results agree with the simulation results. The 3 dB fractional bandwidth errors of the two operating bands are 0.5% and 1%, respectively.

Abstract To address the growing demand for customized Helmholtz acoustic metamaterials, a deep learning driven framework is developed for rapid performance prediction and on demand inverse design. In the first stage, a theoretical model of Helmholtz resonant cavities is established, and its validity is confirmed through finite element simulations and experimental measurements. Based on the theoretical model, a comprehensive dataset is generated, and a deep learning prediction model combining a multilayer perceptron with an attention mechanism is constructed to achieve accurate mapping from geometric parameters to sound absorption spectra. In addition, an inverse design model based on an autoencoder architecture is developed to infer structural parameters from desired sound absorption curves, thereby establishing a bidirectional relationship between acoustic performance and geometry. The proposed deep learning framework shows high prediction accuracy across a broad frequency range, with the inversely derived geometric parameters exhibiting excellent agreement with theoretical calculations. Moreover, the reconstructed absorption spectra closely match the target curves. These findings confirm that the deep learning based methodology provides an efficient, accurate, and generalizable approach for both forward and inverse design of Helmholtz resonant structures, offering a promising route for the rapid development and practical implementation of next generation acoustic metamaterials.

High-resolution short-wave infrared (SWIR) imaging requires photodetectors (PDs) with simultaneously low dark current and high responsivity. To achieve this goal, we demonstrate low-defect bulk germanium-on-insulator (bulk-GeOI) PDs designed for enhanced 1550 nm absorption and suppressed dark current via a resonant cavity and low-defect material platform. Devices were fabricated by direct bonding low-defect bulk Ge and thinning it to ~1300 nm, with an intrinsic layer thickness of only 800 nm. This design avoids epitaxial defects to lower intrinsic dark current while forming a resonant cavity for enhanced responsivity at 1550 nm. Precise doping and Al2O3/Si3N4 bilayer sidewall passivation were employed. From a design perspective, using low-defect bulk Ge minimizes the defects from epitaxial growth and reduces intrinsic dark current, while thinning the Ge layer enhances the resonant cavity effect to improve 1550 nm responsivity. Experimentally, despite the thin absorbing layer, our devices achieved nA-level dark currents (e.g., 18 nA at -1 V for 10 μm devices) alongside high responsivities. Detailed analysis indicates that this dark current is predominantly attributed to surface and sidewall defects from mesa etching, with minimal contribution from low-defect bulk material defects, validating the effectiveness of the bulk-Ge approach in suppressing intrinsic bulk leakage. Optically, the devices achieved high responsivities of 0.85 A/W (1310 nm) and 0.72 A/W (1550 nm), corresponding to external quantum efficiencies of 80.6% and 57.7%, respectively. This work establishes the bulk-GeOI platform as a promising path toward high-performance SWIR PDs, successfully decoupling high responsivity from bulk leakage and paving the way for future gains through refined surface and interface engineering.

Multi-band controllable acoustic topological insulator based on stacked composite resonant cavities

Three-dimensional simulation research on plasma uniformity engineering: diamond film uniformity regulation based on resonant cavity structural resonance design

Construction and photothermal properties of microsphere-modified cavity resonator absorbers with ultra-wide infrared spectrum absorption

Abstract High-sensitivity photon detectors are indispensable core components that drive advancements in high-sensitivity detection, low-light imaging, and optical quantum information processing technologies, with significant applications in quantum communication and quantum computing. This study proposes a structural design for superconducting nanowire single-photon detectors (SNSPDs) based on metallic metasurfaces. In this configuration, superconducting nanowires are embedded within a resonant cavity and covered by a metallic metasurface composed of an array of metal nanoparticles. This metallic metasurface exhibits tunable optical response characteristics when illuminated by incident light of varying wavelengths, thereby significantly enhancing the SNSPD’s light absorption performance within the target wavelength band. Numerical simulations indicate that when the incident electric field is parallel to the NbN nanowire, the absorption efficiency of a curved NbN nanowire with a fill factor of 0.14 exceeds 92% at 1550 nm. This result demonstrates excellent photon trapping capability, suggesting potential for improving the device’s detection efficiency.

The paper is a thorough review of high-gain antenna concepts of microstrip antennas to fifth-generation (5G) and next-generation (6G) wireless communication systems. The reason behind the extensive implementation of microstrip antennas includes their small shape, simple integration capabilities and reduced costs of fabrication. Nevertheless, the traditional designs have inherent drawbacks such as low gain, low bandwidth and high losses at high frequencies.These limitations do not enable them to amplify 5G/6G applications to longer ranges and data rates of extreme resolution. To solve these issues, general strategies are rigorously analyzed. These are metasurface loading to do wave front manipulation and to focus frequencies; frequency-selective surface (FSS) reflectors to create resonant cavity and a gain enhancement of forward radiations; optimization of dielectric substrates with low-loss ceramics and new fabrication; and array configurations that provide gain superposition. The review identifies the performance trade-offs in one technique and underlines the cooperative approach to the design. Balanced gains, bandwidth, profile, and compatibility are made at the cost of composite structures, multi-objective optimization algorithms, and system-level integration. The problems of processing complexity, material losses in millimeter-wave bands, and computing needs are examined nowadays. Intelligent surfaces should move towards reconfigurable surfaces, intelligent design, heterogeneous chip integration, and sensing-communication co-arrangement to support 6G requirements. The paper offers a lot of insights and references into the high-gain microstrip antenna technologies in the next-generation wireless networks.

This study investigates the influence of cavity configuration on the performance of two-dimensional (2D) photonic crystal (PhC) sensors, with particular emphasis on the effect of doubling the number of cavities. A comparative analysis between single-cavity and dual-cavity configurations is conducted to evaluate their impact on key sensing parameters. In the dual-cavity configuration, two resonant cavities are introduced between coupled waveguides, enabling strong optical mode coupling and enhanced electromagnetic field confinement within the sensing region. This coupling leads to sharper resonance peaks, reduced linewidths, and increased interaction between the optical field and the infiltrated analyte. As a result, the dual-cavity sensor exhibits significantly improved sensing performance, achieving a high sensitivity of 9261.54 nm/RIU, a quality factor of 15,352.38, a figure of merit exceeding 4.5 × 107, and a detection limit below 1.7 × 10−7 RIU. These results demonstrate that doubling the cavity number effectively amplifies light–matter interaction and resonance stability, making the proposed dual-cavity 2D PhC sensor a highly promising platform for precise refractive index sensing in biomedical applications.

We develop a fully computational framework to simulate exciton-polaron-polariton formation in moiré superlattices under strong light-matter coupling. The model combines parametrized moiré potentials with analytical cavity representations and non-Hermitian quantum propagation to capture hybridization between moiré-confined excitons and cavity photons. The present model uses a reduced first-harmonic parametrization of the moiré potential and omits atomic-scale reconstruction and material-specific microscopic details. Even so, it captures the leading energy modulation and provides qualitative polariton dynamics predictions relevant to current experiments. The calculated detuning-coupling map reveals the onset of strong coupling near gX ≈ 0.035 eV, yielding a transient Rabi splitting of ħΩR ≈ 6 meV that collapses within 0.3 ps due to carrier-induced dephasing. Time-resolved spectra show ultrafast conversion from neutral excitons to exciton-polarons with formation and depletion times of τAP ≈ 0.24 ps and τX0 ≈ 0.27 ps, respectively. Principal component and Bayesian analyses quantitatively recover the optimal coupling (gX ≈ 0.034 eV) and cavity resonance (EC ≈ 1.72 eV), consistent with reported Rabi splittings in twisted TMD nanocavity systems. This work provides a predictive computational platform for understanding correlated exciton-photon phenomena in two-dimensional moiré quantum materials.

Biosensors have been extensively investigated for the diagnosis, monitoring, and treatment of diseases due to their high sensitivity, fast response, and potential for real-time detection. Among different optical architectures, porous silicon microcavities stand out because of their tunable optical properties, high surface area, and compatibility with biomolecular immobilization. In this work, porous silicon microcavities were fabricated by electrochemical anodization and structurally and optically characterized in order to investigate the key fabrication parameters and assess their suitability as optical transducers for biosensing applications. The microcavities were designed by inserting a defect layer between two Bragg mirrors, using different numbers of periods and anodization conditions. Structural characterization was performed by scanning electron microscopy, while optical behavior was analyzed through reflectance spectroscopy, confirming the formation of a photonic bandgap and a well-defined cavity resonance. In addition, a literature review was conducted to identify the most relevant parameters used for the characterization and validation of porous silicon microcavity-based biosensors, including sensitivity, limit of detection, and quality factor. The results indicate that microcavities with a reduced number of Bragg mirror periods can preserve optical confinement while enhancing molecular infiltration, which is a critical requirement for high-performance biosensors.

Normal-conducting radio frequency cavities are essential in particle accelerators, but their operational stability is often compromised by thermal-induced resonant frequency detuning during high-power operation. This paper introduces a digital low-level radio frequency system that performs autonomous frequency tracking and compensation in a standalone configuration. Specifically, during powering up and rf conditioning, the tracking operates without dependence on external instrumentation. The system employs a vector modulator driven by two orthogonal analog sinusoids of equal amplitude to modulate the reference signal, achieving an adjustable output bandwidth of ± 1.5 6 MHz with a precision of 95.3 Hz entirely within the LLRF framework. A phase-locked loop controller embedded in the system dynamically synchronizes the rf frequency to the cavity resonance, while a real-time spectrum analyzer implemented in the FPGA monitors frequency deviations in a closed-loop manner. Experimental results verify that the system can resolve spectral components within a 1.56-MHz bandwidth and generate arbitrary-frequency rf signals over a 3-MHz span using only its integrated LLRF resources. In high-power tests, the embedded PLL-based tracking maintained the reflected power at 8.5% of the incident power under thermal detuning exceeding 200 kHz, thereby ensuring operational stability through a unified LLRF-based approach.

Second-harmonic generation (SHG) is a key nonlinear optical effect that only occurs in the absence of inversion symmetry. While centro-symmetric materials based on that definition would not sustain an SHG signal, the presence of an interface in a thin film can lead to a local deviation from the inversion symmetry and, hence, to a local second-order hyperpolarizability. To give rise to a notable SHG signal, the inversion symmetry needs to be broken at a global scale, suggesting that at least three materials must be stacked in an alternating manner when thin films are considered. Although such materials can be implemented with surface-anchored metal–organic frameworks (SURMOFs), their suitability for generating a strong second-order nonlinear response has remained unexplored so far. Here, we numerically investigate SHG from thin films of three different SURMOFs stacked above each other using a scale-bridging multi-scale framework combining precise quantum chemistry and fast Maxwell optical simulations. We determine the impact of the thickness of each SURMOF layer on the SHG signal. Our results indicate that interfaces between materials with similar SURMOF parameters contribute little to SHG, whereas interfaces to the surrounding dominate the response. Moreover, we demonstrate that the SHG signal can always be significantly boosted at specific total film thicknesses due to cavity resonances. At these resonances, reducing the individual layer thicknesses to the molecular scale, thereby allowing the film to behave as a bulk material composed almost entirely of interfaces, leads to a two-fold increase in the SHG signal compared to films with thicker layers. This introduces a trade-off between simpler fabrication and the enhanced SHG achievable with ultrathin layers. Our findings highlight the importance of interface effects in designing layered SURMOF structures with optimized nonlinear optical properties, offering guidance for future material explorations.

Single photons in Laguerre-Gaussian (LG) beams, which carry orbital angular momentum (OAM), could enable more robust and efficient photonic quantum communication and information processing, as well as enhanced sensitivity in quantum metrology and imaging. However, as most implementations are indirect or require additional mode-shaping elements, the direct generation of single photons with OAM has received growing interest. Colloidal lead halide perovskite quantum dots (QDs) have recently emerged as a versatile material that can produce indistinguishable single photons quasi-deterministically at a high rate. Here, we integrate single CsPbBr3 QDs into an open Fabry-Perot microcavity with a nanofabricated Gaussian-shaped deformation, demonstrating Purcell-enhanced single-photon generation into individual cavity modes with up to 18.1 ± 0.2 times accelerated decay, down to tens of picoseconds. By in situ tuning of the cavity resonance, we can selectively couple a single QD to different LG modes and observe the spatial patterns of the generated single-photon beams emitted from the cavity. Our findings may guide the development of high-photon-rate sources that directly generate single-photon LG beams for advanced quantum photonic applications.

ABSTRACT This work proposes a substrate integrated waveguide (SIW) stacked filtering antenna for 5 G millimeter-wave applications, featuring broadband operation and high selectivity. The antenna integrates a dual-layer structure: a SIW cavity with an etched rectangular slot and symmetric C-shaped Defected Ground Structure (DGS) in the feeding layer, and four truncated-corner patches as radiators. Due to the perturbation of the rectangular slot, two resonant modes are generated in the SIW resonant cavity, and a radiation null is introduced to improve the out-of-band suppression. The slot couples with the upper 2 × 2 patch array, generating a third resonant mode and broadening the bandwidth. The energy radiated by the 2 × 2 patches superimposes in phase, significantly enhancing the gain. Furthermore, the DGS suppresses unwanted interference modes in the SIW, introduces a radiated null point that results in a filtering response, and provides additional resonant modes to further extend the bandwidth. To validate the design, the prototype of the antenna is fabricated and measured, and the measured results show that the proposed antenna has a −10 dB impedance bandwidth of 16.91% (24.13 ~ 28.59 GHz), a stable practical boresight gain of 4.5 to 6.2 dBi in the operating band, and >15 dB out-of-band rejection.

This work presents microwave sensing of ethanol concentration in ethanol–water mixtures using a low-cost 3D-printed cavity resonator. The objective is to realize a customizable liquid sensor that combines high measurement accuracy with inexpensive, in-house fabrication. The cylindrical cavity is fabricated from polylactic acid using fused deposition modeling and metallized on its inner surface with copper tape. The resonator operates in the TM010 mode with a resonant frequency of 3 GHz. A standard 1.5 mL centrifuge tube is used as a modular sample holder and inserted through a circular opening in the top endcap of the cavity. The quality factor of the air-filled cavity is 200, which decreases to 37.3 when the cavity is loaded with deionized water. As an application example, ethanol concentrations in ethanol–water mixtures are determined using both the resonant frequency and the peak magnitude of the transmission coefficient (|S21|). For ethanol concentrations between 20% and 100%, the concentration can be accurately extracted from the resonant frequency alone: a quartic calibration curve yields a coefficient of determination R2=0.9992, an average sensitivity of approximately 8.4 MHz/% ethanol, and a mean absolute error of about 0.58% on the calibration set. In addition, a cubic calibration based on the peak ∣S21∣ over the 0–90% concentration range achieves a mean absolute error of approximately 0.52% on the calibration set and about 0.55% on an independent validation set covering 5–85% ethanol. Comparison with conventionally machined metal cavities shows that the proposed 3D-printed cavity achieves a high Q-factor at significantly lower cost and can be fabricated in-house using a standard 3D printer. These results demonstrate metrologically relevant performance in terms of low error and high sensitivity using a low-cost and easily replicable platform for microwave liquid sensing in biomedical and chemical engineering applications.

This paper presents a nanoscale sensor based on a metal-insulator-metal (MIM) waveguide coupled with a composite resonant cavity, where the ring resonator is embedded with triangular, semicircular, and rectangular structural elements. The transmission characteristics and sensing performance of the structure were systematically analyzed using the finite element method. The results indicate that the interference between the continuous mode in the waveguide and the discrete mode in the resonant cavity generates a distinct asymmetric Fano resonance. The optimized sensor achieves a sensitivity of 2960 nm/RIU and a figure of merit (FOM) of 59.79. Experimental verification confirms that the structure exhibits high responsiveness in temperature sensing, providing an effective solution for integrated photonic devices.

ABSTRACT A narrowband all‐dielectric absorber capable of covering the long‐infrared band is designed. The structure of this absorber consists of an upper dielectric layer, a lower dielectric substrate, and a reflective layer. The absorption bandwidth of the absorber is 5 µm for an absorption greater than 90%. The absorber demonstrates polarization‐insensitive and large‐angle absorption characteristics in the wavelength range of 6–18 µm. To further broaden the absorption bandwidth, a broadband metamaterial absorber (BMA) was designed, which consists of a top Ti layer, middle and lower Si 3 N 4 dielectric layers, and a substrate layer. The absorption bandwidth of the BMA is 10.5 µm, with an average absorption of up to 92.5% in the 6–18 µm wavelength range. The BMA exhibits polarization‐insensitive and large‐angle absorption characteristics. At a 60° incident angle under TM and TE modes, the average absorption is 89% and 77%, respectively. The high absorption and broadband characteristics of the absorber are mainly attributed to the synergistic effect of localized surface plasmon resonance, propagating surface plasmon resonance, and cavity resonance, which jointly dominate the absorption process. This high‐performance absorber has promising development prospects in cutting‐edge fields such as infrared detection, stealth technology, and sensing.