Search Results (779)

Evaporation Duct Height (EDH) is a crucial parameter in evaporation duct modeling, as it directly influences the strength of the waveguide trapping effect and significantly impacts the over-the-horizon detection performance of maritime radars. To address the limitations of low prediction accuracy and limited interpretability in existing deep learning models under complex marine meteorological conditions, this study proposes a surrogate model, BLA-EDH, designed to emulate the output of the Naval Postgraduate School (NPS) model for real-time EDH estimation. Experimental results demonstrate that BLA-EDH can effectively replace the traditional NPS model for real-time EDH prediction, achieving higher accuracy than Multilayer Perceptron (MLP) and Long Short-Term Memory (LSTM) models. Random Forest analysis identifies relative humidity (0.2966), wind speed (0.2786), and 2-m air temperature (0.2409) as the most influential environmental variables, with importance scores exceeding those of other factors. Validation using the parabolic equation shows that BLA-EDH attains excellent fitting performance, with coefficients of determination reaching 0.9999 and 0.9997 in the vertical and horizontal dimensions, respectively. This research provides a robust foundation for modeling radio wave propagation in the Yellow Sea and Bohai Sea regions and offers valuable insights for the development of marine communication and radar detection systems. Full article

Polymeric optical waveguides represent an essential component in photonic technology thanks to their ability to guide light through controlled structures, enabling applications in telecommunications, sensors, and integrated devices. With the development of new materials and increasingly versatile manufacturing methods, these structures are being integrated into various systems at a rapid pace, while their dimensions are constantly being reduced. This article explores the main fabrication methods for polymeric optical waveguides, such as traditional and maskless photolithography, laser ablation, hot embossing, nanoimprint lithography, the Mosquito method, inkjet printing, aerosol jet printing, and electrohydrodynamic (EHD) printing. The operating principle of each method, the equipment and materials used, and their advantages, limitations, and practical applications are evaluated, in addition to the propagation losses and characterization of the waveguides obtained with each method. Full article

Augmented reality (AR) displays are pivotal for delivering immersive experiences in the metaverse, thus driving significant research interest. Current AR systems, predominantly relying on diffraction principles, often suffer from low efficiency and face challenges in realizing monolithic full-color operation. Herein, we propose an AR system that integrates a broadband and highly efficient meta-grating in-coupler and an elliptical meta-grating out-coupler onto a single thin glass substrate. The meta-gratings, with unique nanostructures, enable coupling efficiency exceeding 60% for red (R), green (G), and blue (B) wavelengths across the entire field of view (FOV). Image-bearing light is first coupled into a single-layer optical waveguide via the meta-grating, then undergoes two-dimensional expansion through the elliptical meta-grating, and is ultimately coupled into the human eye to form a large AR FOV. Experimentally, we fabricated an optical waveguide prototype and validated the system’s high efficiency and color-enhanced imaging capabilities. This work advances the development of monolithic, trichromatic, highly efficient, and large FOV AR displays based on meta-grating technology. Full article

As a core functional device in microwave systems, attenuators play a crucial role in key aspects such as signal power regulation, amplitude attenuation, and impedance matching. Addressing the pressing technical issues currently exposed by attenuators in practical applications, such as excessive insertion loss, low attenuation accuracy, large physical dimensions, and insufficient process reliability, this paper proposes a design scheme for an RF three-bit reconfigurable stepped attenuator based on radio frequency micro-electromechanical systems (RF MEMS) switches. The attenuator employs planar integration of the T-type attenuation network, Coplanar Waveguide (CPW), Y-shaped power divider, and RF MEMS switches. While ensuring rational power distribution and stable attenuation performance over the full bandwidth, it reduces the number of switches to suppress parasitic parameters, thereby enhancing process feasibility. Test results confirm that this device demonstrates significant advancements in attenuation accuracy, achieving a precision of 1.18 dB across the 0–25 dB operational range from DC to 20 GHz, with insertion loss kept below 1.65 dB and return loss exceeding 12.15 dB. Additionally, the device boasts a compact size of merely 0.66 mm × 1.38 mm × 0.32 mm, significantly smaller than analogous products documented in existing literature. Meanwhile, its service life approaches 5 × 10⁷ cycles. Together, these two attributes validate the device’s performance reliability and miniaturization advantages. Full article

Lithium niobate (LN) materials have become a key platform for constructing core optoelectronic devices such as electro-optic (EO) modulators, optical frequency combs, and integrated optical waveguides, owing to their broad transparent window, mature waveguide processes, and excellent electro-optic effect. They demonstrate revolutionary application value in light source generation, signal transmission, and intensity modulation of optical communication systems, and are hailed as the “silicon of the photonics field,” attracting significant attention from both academia and industry. Especially with the commercialization of high-quality thin-film lithium niobate (TFLN) materials, the performance of thin-film optoelectronic devices based on waveguide structures has achieved leapfrog improvements, with their loss characteristics and modulation bandwidth far exceeding those of traditional bulk material devices. This paper systematically combs the photonic properties of LN materials, introduces in detail the electro-optic effect and electro-optic modulation principle of LN electro-optic modulators, reviews some recent research achievements of scholars, focuses on expounding the preparation processes of waveguide-based TFLN, the types of waveguide-based optoelectronic devices, and the research progress of these devices, and discusses and compares the advantages and development potential of different routes. Full article

In order to solve the problem of the efficiency reduction and complex manufacturing of traditional grating couplers under environmental temperature fluctuations, a Si₃N₄ high-efficiency grating coupler integrating a distributed Bragg reflector (DBR) and thermo-optical tuning layer is proposed. In this paper, the double-layer DBR is used to make the down-scattered light interfere with other light and reflect it back into the waveguide. The finite difference time domain (FDTD) method is used to simulate and optimize the key parameters such as grating period, duty cycle, incident angle and cladding thickness, achieving a coupling efficiency of −1.59 dB and a 3 dB bandwidth of 106 nm. In order to further enhance the temperature stability, the amorphous silicon (a-Si) thermo-optical material layer and titanium metal serpentine heater are embedded in the DBR. The reduction in coupling efficiency caused by fluctuations in environmental temperature is compensated via local temperature control. The simulation results show that within the wide temperature range from −55 °C to 150 °C, the compensated coupling efficiency fluctuation is less than 0.02 dB, and the center wavelength undergoes a blue shift. This design is compatible with complementary metal-oxide-semiconductor (CMOS) processes, which not only simplifies the fabrication process but also significantly improves device stability over a wide temperature range. This provides a feasible and efficient coupling solution for photonic integrated chips in non-temperature-controlled environments, such as optical communications, data centers, and automotive systems. Full article

Augmented reality (AR) technology blends digital content with the real world to create immersive experiences. Diffractive waveguides, a key AR component, are popular because they balance weight, size, image quality, and ease of production. However, traditional glass-based waveguides have drawbacks like narrow viewing angles, blurry images, and rainbow-like distortions. To solve these issues, we developed ultra-thin, lightweight AR glasses using silicon carbide (SiC) and a new design method called the Period-Limited theory (PL theory). Our simulations show that the system works efficiently across red, green, and blue colors, removing rainbow distortions while keeping images clear and vibrant. Tests confirm that the design eliminates rainbow effects, provides a wide 55° field of view (FOV), and keeps each lens extremely light (just 2.12 g). This work offers a practical way to make compact, high-performance AR glasses with excellent display quality. Full article

This paper proposes and experimentally demonstrates a novel physical-layer encryption scheme for terahertz (THz) wireless communication based on a logical AND operation between dual THz beams transmitted from spatially separated sources. Unlike previous studies, confined to chip-scale or waveguide configurations, our approach validates the concept under free-space transmission, thereby highlighting its applicability to real wireless environments. The system utilizes uni-traveling carrier photodiodes (UTC-PDs) to generate independent THz carriers, and coherent detection combined with envelope extraction enables analog-domain realization of the AND operation. Experimental results confirm successful decryption at data rates up to 1.5 Gbit/s, achieving bit error rates (BERs) below the forward error correction threshold (e.g., 3.13 × 10⁻¹⁰ at 500 Mbit/s). Furthermore, spatial mapping and simulation show strong agreement with measurements, yielding a predictive accuracy of approximately 84% and validating spatial selectivity as a security feature. These findings establish the novelty of applying dual-beam logical operations for secure THz transmission and provide a foundation for scalable, low-complexity physical-layer security in next-generation wireless networks. Full article

This paper presents a triple-ring optical filter designed through direct binary search inverse design, comprising three cascaded rings in an add–drop configuration. We established a physical model using temporal coupled-mode theory to derive theoretical spectra and analyze key transmission parameters. Subsequently, we encoded the target transmission performance into a figure of merit to optimize the coupling coefficients between ring resonators and waveguides. We verify the theoretical parameters using three-dimensional finite-difference time-domain simulations. The optimized filter achieves a free spectral range of 86 nm, an insertion loss of 0.4 dB, an extinction ratio of 20 dB, and a narrow spectral linewidth of 0.2 nm within a compact footprint of $29 \mathsf{\mu }\mathrm{m}\times 46.5 \mathsf{\mu }\mathrm{m}$. This device demonstrates significant application potential, particularly in laser external cavities, dense wavelength division multiplexing systems, and sensing applications. Furthermore, this work provides a systematic design framework for the precision design of photonic devices. Full article

This paper presents the design and performance evaluation of a compact four-element coplanar waveguide (CPW)-fed antenna array operating in the 3.3–3.6 GHz frequency band. The proposed antenna is tailored for sub-6 GHz 5G New Radio (NR) applications, specifically aligning with the n77/n78 bands widely adopted for mid-band 5G deployment. The CPW feeding technique enables low-profile integration and ease of fabrication, while the multi-element configuration supports enhanced gain and spatial diversity. Both simulated and measured results demonstrate good impedance matching (|S₁₁| < −10 dB), stable radiation patterns, and inter-element isolation suitable for MIMO operation. The design offers a promising solution for compact 5G antenna systems and can be extended to future wireless communication platforms requiring high efficiency and compact form factors. Full article

Meta-optics, enabled by metasurfaces consisting of two-dimensional arrays of meta-atoms, offers ultrathin and multi-functional control over the vectorial wavefront of light at subwavelength scales. The unprecedented optical element technology is a promising candidate to overcome key limitations in augmented reality (AR) and virtual reality (VR) near-eye displays particularly in achieving compact, eyeglass-type form factors with a wide field-of-view, a large eyebox, high resolution, high brightness, and reduced optical aberrations, at the same time. This review highlights key performance bottlenecks of AR/VR displays in the perspective of optical design, with an emphasis on their practical significance for advancing current technologies. We then examine how meta-optical elements are applied to VR and AR systems by introducing and analyzing the major milestone studies. In case of AR systems, particularly, two different categories, free-space and waveguide-based architectures, are introduced. For each category, we summarize studies using metasurfaces as lenses, combiners, or waveguide couplers. While meta-optics enables unprecedented miniaturization and functionality, it also faces several remaining challenges. The authors suggest potential technological directions to address such issues. By surveying recent progress and design strategies, this review provides a comprehensive perspective on the role of meta-optics in advancing the optical engineering of next-generation AR/VR near-eye displays. Full article

Although epsilon-near-zero (ENZ) media have emerged as a promising platform for power dividers, the majority of existing designs are confined to fixed power splitting. In this work, two dynamically tunable power dividers using waveguide ENZ media are proposed by precisely modulating the internal magnetic field and the widths of the output waveguides. The first approach features a mechanically reconfigurable ring-shaped ENZ waveguide. By continuously re-distributing the magnetic field within the ENZ tunneling channels utilizing rotatable copper plates, arbitrary power division among multiple output ports is constructed. The second design integrates a rectangular-loop ENZ cavity into a substrate-integrated waveguide, with four positive–intrinsic–negative diodes embedded to dynamically activate specific output ports. This configuration steers electromagnetic energy toward output ports with varying cross-sectional areas, enabling on-demand control over both the power division and the number of output ports. Both analytical and full-wave simulation results confirm dynamic power division, with transmission efficiencies exceeding 93%. Despite differences in structure and actuation mechanisms, both designs exhibit flexible field control, high reconfigurability, and excellent transmission performance, highlighting their potential in advanced applications such as real-time wireless communications, multi-input–multi-output systems, and reconfigurable antennas. Full article

Narrow-linewidth broadband tunable external cavity diode lasers (NBTECDLs), with their broadband tuning range, narrow linewidth, high side-mode suppression ratio (SMSR), and high output power, have become important laser sources in many fields such as optical communication, spectral analysis, wavelength division multiplexing systems, coherent detection, and ultra-high-speed optical interconnection. This paper briefly describes the basic theory of NBTECDLs, introduces NBTECDLs with diffraction grating type, fiber Bragg grating (FBG) type, and waveguide type, and conducts an in-depth analysis on the working principles and performance characteristics of NBTECDLs based on different NBTECDL types. Then, it reviews the latest research progress on Littrow-type, Littman-type, FBG-type, and waveguide-type NBTECDLs in detail and compares and summarizes the characteristics of Littrow-type NBTECDLs, Littman-type NBTECDLs, FBG-type NBTECDLs, and waveguide-type NBTECDLs. Finally, it looks at the structural features, key technologies, optical performance, and application fields of the most cutting-edge research in recent years and summarizes the challenges and future development directions of NBTECDLs. Full article

Waveguide-integrated metasurfaces offer a promising platform for ultracompact on-chip optical systems, enabling applications such as fluorescence sensing, holography, and near-eye displays. In particular, integrated achromatic metalenses that couple guided modes to free-space radiation are highly desirable for single-molecule fluorescence sensing, where high numerical aperture (NA), efficient light focusing, and consistent focal volume overlap across excitation and emission wavelengths are critical. However, designing integrated high-NA metalenses with multi-wavelength operation remains fundamentally challenging due to the wavelength-dependent propagation of guided modes. Here, we present an inverse design framework that simultaneously optimizes the geometries and positions of silicon nitride nanofins atop a slab waveguide to achieve diffraction-limited focusing at three wavelengths with unity NA. The resulting metalens outperforms conventional segmented designs in focusing efficiency and sidelobe suppression, particularly at wavelengths corresponding to the excitation and emission bands of the model fluorophore Alexa Fluor 647. Numerical analysis shows that the design yields a high molecule detection efficiency suitable for epi-fluorescence single-molecule sensing. This work highlights the potential of inverse-designed metalenses as a versatile on-chip platform for advanced applications in fluorescence spectroscopy, augmented reality, or optical trapping. Full article

A low-profile beam-scanning antenna array for cost-effective 5G millimeter-wave (mmWave) applications is proposed in this work. The array features a compact single-layer substrate structure while achieving a wide operating bandwidth covering the 5G n257 band (26.5–29.5 GHz). A novel antenna element is first designed and analyzed, employing a metallic rectangular patch with shorting pins as the radiator, excited through a modified coplanar waveguide (CPW) feeding structure. Based on this element, four-element and eight-element linear arrays are developed with an overall profile of only 0.07 λ at 28 GHz and fabricated to experimentally assess beam-scanning performance. To accurately characterize and validate the radiation behavior, an mmWave beam box system is utilized for pattern measurements. The results demonstrate that the fabricated arrays achieve an impedance bandwidth fully covering the 5G n257 band with VSWR < 2, while the measured beam-scanning performance closely agrees with simulations. These findings confirm that the proposed design and its extensions offer strong potential for practical integration into future 5G mmWave communication devices. Full article