Incident Angle Research Articles

On-Chip Polarization Rotators Using Metasurface.

Metasurfaces, with their ability to finely manipulate light properties (e.g., polarization), represent a frontier in optical technology. Here, we report innovative gold-based metasurfaces that are adept at changing the light polarization across a broad range of incident angles. Their expansive acceptance angle facilitates seamless integration with silicon waveguides, culminating in the realization of a novel, compact, broadband, and low-loss on-chip polarization rotator. The demonstrated metasurface devices show polarization conversion efficiencies as high as 98.5% at 1550 nm in the free space measurements. Unlike conventional plasmonic metasurfaces, which lack broadband capabilities, our metasurface-based waveplates show extinction ratios of >15 dB for a 120 nm bandwidth. These metasurfaces are positioned on top of up-reflecting mirrors fabricated in a micrometer-scale silicon-on-insulator platform to demonstrate on-chip polarization rotation. The demonstrated polarization rotator shows an extinction ratio of more than 10 dB for a 100 nm bandwidth. This study marks the first successful demonstration of on-chip polarization manipulation utilizing metasurface integration, heralding significant potential impacts for enhancing the functionality and miniaturization of photonic integrated circuits.

Multifunctional daytime radiative cooler resistant to UV aging

Passive radiative cooling presents a promising approach to mitigate global warming and reduce energy consumption. Existing coolers, however, face challenges in practical prolonged adoption due to their unappealing design, susceptibility to environmental pollutants, as well as degradation of polymers by ultraviolet (UV) irradiation from sunlight. This study introduces a multifunctional daytime radiative cooler (MDRC) with a dual-layered structure, combining practical functionality with aesthetic value. Its base layer consists of an Ag–TiO2–Ag thin film stack, imparting vibrant cyan, magenta, and yellow colors, even maintaining visually appealing from various incident angles, up to 75°, to ensure consistent color display. The top layer, comprising S–SiO2 nanospheres with UV resistance rather than polymers, not only forms a superhydrophobic surface with a contact angle of 155.502°, enhancing the self-cleaning capability of the MDRC against contamination and dust, but also renders the MDRC with extraordinary anti-aging capacity. Outdoor experiments has shown that the MDRC maintains operation at temperatures above ambient under direct solar irradiation, achieving a substantial temperature reduction of 6.82 °C compared to the same colored commercial coating. After three months of outdoor exposure, the MDRC demonstrated minimal degradation in performance, with decreases of only 0.29 °C during the day and 0.12 °C at night, underscoring its superior UV-resistant aging properties. This MDRC represents a robust solution for diverse durable outdoor raidative cooling applications, advancing toward real-world utilization.

Non-reciprocal optical Tamm state in a photonic crystal heterojunction containing Weyl semimetals

In the past decades, optical Tamm states (OTSs) in photonic crystal (PC) heterojunctions containing magneto-optical materials have been widely utilized to achieve non-reciprocal transmission. Nevertheless, as incident angle increases, both forward and backward OTSs in PC heterojunctions containing magneto-optical materials shift toward shorter wavelengths (i.e., blueshift), giving rise to weak non-reciprocities. In this paper, we achieve a non-reciprocal OTS in a PC heterojunction containing Weyl semimetals (WSMs). Interestingly, as incident angle increases, the forward OTS shifts towards longer wavelengths while the backward OTS shifts toward shorter wavelengths. Therefore, the non-reciprocity can be greatly enhanced. The underlying physical mechanism can be explained by the Fabry-Perot resonant condition. Besides, the effects of the axial vector b and the loss of WSM on non-reciprocity are investigated. These results would possess great potential applications in the design of circulators and isolators.

High sensitivity fiber SPR sensor based on a spiral coarse cone structure.

A fiber SPR sensor can achieve rapid and portable detection of trivalent arsenic ions (As3+) in drinking water or food, but their sensitivity and detection limit need to be further improved and developed toward specific detection. This article proposed the implementation of the SPR sensor using a biased core fiber spiral coarse cone structure. The fine core of the biased core fiber was used to reduce the mode of transmitted light. By controlling the pitch of the spiral core to control the SPR incidence angle, a significant increase in the sensitivity of the fiber SPR sensor was achieved. Meanwhile, the harmless glutathione (GSH) was modified on the surface of the sensing gold film to achieve the specific detection of As3+. The experimental results indicate that the spiral coarse cone fiber SPR sensor proposed in this article has a detection sensitivity of 32.48 nm/ppb for As3+, with a detection limit as low as 0.011 ppb, meeting the detection requirements of the World Health Organization for As3+ in water, which provides a new feasible solution for fast, portable, and highly sensitive detection of metal ions in water and food.

PVDF/Al2O3/Gd2O3 layers splitter with first-order suppression functionality

In the realm of optical component design, the proposed multilayer grating splitter represents a significant breakthrough. For the triple-layered grating in this paper, it combines the outstanding optical properties of polyvinylidene fluoride (PVDF), aluminum oxide (Al2O3), and gadolinium oxide (Gd2O3) to achieve high-efficiency outputs for both the 0th and −2nd orders under secondary Bragg angle incidence conditions. The diffraction efficiencies for both TE and TM polarizations exceed 97%, with energy uniformity surpassing 99%. These results highlight the potential of this design in precision beam control applications. The splitter's performance benefits from the intrinsic material properties and optimally designed structural dimensions, which enhance transparency and thermal stability under operational conditions. Through rigorous design and optimization, including modal methods and simulated annealing algorithms, the device achieves exceptional uniformity in diffraction efficiency, which is crucial for high-resolution spectroscopy and precision optical measurement applications.

Multi-band enhanced nonreciprocal thermal radiation based on Weyl semimetals

Previous studies manifested that the majority of structures that exhibit nonreciprocal thermal radiation in the mid-infrared are capable of achieving either single-band strong nonreciprocity or multi-band weak nonreciprocity at a large incidence angle. However, few structures can realize multi-band strong nonreciprocity at a small incidence angle. To address such scientific issues, we propose a tunable nonreciprocal thermal emitter based on gallium arsenide (GaAs)/graphene/Weyl semimetal (WSM). This device is capable of achieving strong nonreciprocity at 7.3 μm, 10 μm and 13.6 μm wavelengths at an incidence angle of 25.5°. It is shown that the field enhancement of the GaAs/graphene composite layer can improve the nonreciprocal response of the WSM layer. In addition, by changing the Fermi energy level of graphene and the axial vector b of the Weyl semimetal, tunable nonreciprocal thermal radiation can be realized. What's more, we find that the structure breaks Kirchhoff's law without lithography and an external magnetic field, which reveals the advantages of applying our research in the field of thermal radiation.

Anti-penetration properties of negative Poisson’s ratio honeycomb sandwich structure filled with foam

The ballistic responses of negative Poisson’s ratio honeycomb sandwich structures filled with aluminum foam are investigated using numerical simulation method. The residual velocity of the projectile, the energy absorption, and the failure forms of the sandwich structures are systematically analyzed. The influence of the impact position and incidence angle of the projectile, wall thickness, and concave angle of honeycomb, as well as the thickness of the front and back sheets of the structure on the penetration resistance is discussed. The results show that the foam-filled honeycomb sandwich structure has a better penetration resistance than the foam core sandwich structure with the same areal density, and the penetration resistance of the foam-filled honeycomb sandwich structure can be improved by designing its geometric parameters.

Enhancing payload capacity to low earth orbit via a relay solution trajectory with laser-powered vehicles

ABSTRACT Low Earth Orbit (LEO) stands as the primary access point for deep space exploration endeavors, encompassing a variety of space missions such as communication satellites, Earth observation platforms, and scientific research missions. In light of the expanding scope of human activities in space, the cost associated with accessing LEO has emerged as a critical focal point for spacecraft designers. Within the spectrum of proposed solutions, laser-powered vehicle has emerged as a viable avenue toward achieving cost-effective launch options. In order to significantly augment the payload capacity of laser-powered launch vehicles destined for LEO, this study introduced a novel Relay Solution Trajectory Flight Scheme. Central to this scheme was the implementation of a relay mirror system affixed to a satellite, which served to stabilize the incident angle of the laser beam directed toward the laser-powered vehicle, thereby ensuring continuous alignment between the laser beam and the vehicle’s axis throughout the duration of the flight. Following the development of comprehensive structural, propulsive, aerodynamic, and trajectory models tailored for the laser-powered vehicle, an optimization of its flight trajectory was conducted, comparing this innovative strategy with two conventional flight strategies. The outcomes of this analysis showcased a notable enhancement of 269.29% in payload capacity compared to conventional strategies that lacked a relay satellite system, within a designated 400 km LEO flight scenario. This endeavor underscored the transformative potential of advanced relay systems in reshaping payload delivery mechanisms and elevating mission feasibility levels, notwithstanding the intricate coordination challenges posed by intricate satellite systems.

Design and application of coal gangue sorting system based on deep learning

With the advancement of science and technology, coal-washing plants are transitioning to intelligent, information-based, and professional sorting systems. This shift accelerates the construction a modern economic system characterized by green and low-carbon development, thereby promoting the high-quality advancement of the coal industry. Traditional manual gangue picking and multi-axis robotic arm gangue selection currently suffer from low recognition accuracy, slow sorting efficiency, and high worker labor intensity. This paper proposes a deep learning-based, non-contact gangue recognition and pneumatic intelligent sorting system. The system constructs a dynamic database containing key feature information such as the target gangue's contour, quality, and center of mass. The system elucidates the relationships between ejection speed, mass, volume, angle of incidence, and the impact energy matching mechanism. Demonstration experiments using the system prototype for coal gangue sorting reveal that, compared to existing robotic arm sorting methods in coal washing plants, this system achieves a gangue identification accuracy exceeding 97%, a sorting rate above 91%, and a separation time of less than 3 s from identification to separation, thereby effectively enhancing raw coal purity.

Klein tunneling and Fabry-Perot resonances in the α - T 3 bilayer with aligned stacking

This paper investigates the quantum tunneling effect on the α − T 3 bilayer with aligned stacking. An effective model is constructed to describe the properties around the triple band crossings for stacking with a vertical alignment of sites in the bilayer system. Focusing on these band crossings, it is found that while the energy spectrum remains gapless throughout, it is characterized by flat energy bands. Subsequently, the transmission coefficient, T, for Dirac quasi-electrons across a rectangular potential barrier is calculated, alongside the relationship between the transmission rate and the coupling parameter α. It is observed that super-tunnel phenomena occur at certain values of the quasiparticle energy, where the transmission is perfect regardless of the angle of incidence on the barrier, with α = 1. Furthermore, it is found that for a wide range of parameter values, the transmittance evolves monotonically and exponentially with increasing alpha. The paper also highlights the occurrence of the Klein paradox in the system, where quasiparticles approaching the barrier with zero-angle incidence exhibit ideal quantum transparency.

Manipulation of Helicity-Dependent Photocurrent and Stokes Parameter Detection in Topological Insulator Bi2Te3 Nanowires.

Helicity-dependent photocurrent (HDPC) and its modulation in topological insulator Bi2Te3 nanowires have been investigated. It is revealed that when the incident plane of a laser is perpendicular to the nanowire, the HDPC is an odd function of the incident angle, which is mainly contributed by the circular photogalvanic effect originating from the surface states of Bi2Te3 nanowire. When the incident plane of a laser is parallel to the nanowire, the HDPC is approximately an even function of the incident angle, which is due to the circular photon drag effect coming from the surface states. It is found that the HDPC can be effectively tuned by the back gate and the ionic liquid top gate. By analyzing the substrate dependence of the HDPC, we find that the HDPC of the Bi2Te3 nanowire on the Si substrate is an order of magnitude larger than that on SiO2, which may be due to the spin injection from the Si substrate to the Bi2Te3 nanowire. In addition, by applying different biases, the Stokes parameters of a polarized light can be extracted by arithmetic operation of the photocurrents measured in the Bi2Te3 nanowire. This work suggests that topological insulator Bi2Te3 nanowires may provide a good platform for opto-spintronic devices, especially in chirality and polarimtry detection.

A method for extracting P‐SV‐converted wave angle‐domain common‐image gathers based on elastic‐wave reverse‐time migration

AbstractMulticomponent seismic technology utilizes the kinematic and dynamic characteristics of reflected P‐waves and converted S‐waves to reduce ambiguity in seismic exploration. The imaging and inversion accuracy of P‐SV‐converted waves are important in determining whether multicomponent seismic exploration can achieve higher exploration accuracy than conventional P‐wave exploration. Pre‐stack inversion of P‐SV‐converted waves requires precise input of P‐SV‐converted wave angle‐domain common‐image gathers. Consequently, the P‐SV‐converted wave angle‐domain common‐image gather extraction accuracy will significantly affect the P‐SV‐converted wave inversion accuracy. However, existing methods for extracting P‐SV‐converted wave angle‐domain common‐image gathers are constrained by issues such as the P‐ and S‐wave crosstalk artefacts, low‐frequency noises and inaccurate calculation of P‐wave incident angles, leading to poor imaging accuracy. We study an angle‐domain cross‐correlation imaging condition and address three key issues based on this condition: the decoupling of P‐ and S‐waves, the separation of up‐going and down‐going waves and the precise calculation of P‐wave incident angles. Our strategies facilitate high‐precision extraction of P‐SV‐converted wave angle‐domain common‐image gathers using elastic wave reverse‐time migration. In this paper, first, we employ the first‐order velocity‐dilatation‐rotation elastic wave equations to decouple P‐ and S‐waves automatically during source and receiver wavefield extrapolations. Second, we calculate the optical flow vectors of P‐ and S‐waves to ensure stable calculations of wave propagation directions. Based on this, we obtain up‐going and down‐going waves of P‐ and S‐waves. Meanwhile, we calculate the incident angle of the source P‐wave using geometric relations. Lastly, we apply the angle‐domain imaging condition to achieve high‐precision extraction of P‐SV‐converted wave angle‐domain common‐image gathers. Model examples demonstrate the effectiveness and advantages of the proposed method.

Enhanced Photoemission Performance of InGaN Inclined Nanowire Array.

We propose to improve the solar energy utilization by using InGaN inclined nanowire array photocathodes. We first study vertical nanowire array. On the basis of vertical nanowire array, we study inclined nanowires by changing the inclination angle of nanowires. The inclined nanowires exhibit higher quantum efficiency at larger period and larger inclination angle. However, the infinite expansion of period will cause its performance to degrade. The quantum efficiency of inclined nanowires with a period of 175 nm and an inclination angle of 5.35° is as high as 80.2% when the incident light angle is irradiated at 5°. In addition, applying an electric field can improve the collection efficiency of inclined nanowires and help them maintain a high collection efficiency over a longer wavelength range. The design principles proposed in this work will provide a theoretical reference for the performance improvement of InGaN photocathodes.

Vanadium dioxide-assisted switching of a half-wave and quarter-wave plate to a dual-band absorber for the terahertz wave

In this study, we present a broadband, multi-functional, and switchable metamaterial for terahertz (THz) waves. The metamaterial design achieves high polarization conversion efficiency and can seamlessly transition between a polarization converter (PC) and a dual-band absorber through the phase transition behavior of vanadium dioxide (VO2). Our design facilitates linear to-cross (Half-wave plate) and linear to-circular (Quarter-wave plate) polarization conversion across a bandwidth extending from 0.58 THz to 0.88 THz, and 0.35 THz to 0.50 THz respectively. Near-perfect absorption at 0.35 THz and 0.99 THz was observed when VO2 changed its phase from an insulator to a conductor. These broadband features are realized through a straightforward metamaterial design incorporating only a reflector, a dielectric spacer, and an antenna (meta-atom resonator). Our designed structure demonstrates impressive angular stability for incident angles ranging from 0° to 45°. The proposed switchable metamaterial holds promise for advancing the development of tunable polarization rotating devices and on/off switching LPC devices, offering broad applications in THz detection, sensing, and communications.

Plane SV-waves scattering by seawater convex surface topography and underlying lined tunnel in a saturated half-space

Analytical solutions of boundary-valued problems for aboveground topography and underground buried structures, especially for sites with overlying seawater, have always been challenging. Based on the region decomposition technique (RDT) and Hankel integral transform method (HITM), SV-waves scattering by the convex circular topography with seawater and underlying tunnel in a saturated half-space is solved. The primary problem is tackling additional scattered waves introduced by the water–soil interface and convex topography, while ensuring boundary conditions are all met. To this end, scattering wave potential functions in cylindrical coordinates are first transformed into the Hankel integral form in Cartesian coordinates. This greatly facilitates the straightforward application of free boundary conditions at the soil–seawater flat interface, rather than making a large circular arc approximate assumption, which, in turn, avoids the resultant accumulating errors. Secondly, scattering problem to be solved is mathematically and analytically formulated as solving a 5 × 5 linear equation system comprised of wave functions inside the convex topography and lining tunnel while satisfying all physical continuous boundary conditions. This is the main innovation and resulting consequence from the theoretical derivation process. Finally, validation of numerical examples between this paper, existing studies and theoretical analysis further demonstrates the reliability and general adaptability of solutions. Parametric studies of the incident SV waves are conducted to investigate the spatially varying seismic response. The effects of SV-waves incident angles and frequencies, tunnel burial depth, tunnel lining thickness, saturated soil porosity, and seawater depth are investigated and analyzed in detail. This study provides a feasible scheme of investigating the dynamic response of complex submarine sites, which is of great significance for both theoretical value and engineering purposes.

Experimental Demonstration of a Broadband Perfect Absorbing Metasurface For Noise And Vibration Attenuation

Recently, we reported a novel design of perfect flexural wave-absorbing metasurface that provides broadband performance and accommodates wide incident angles. The proposed absorber is manufactured using advanced 3D printing technology. The simple design and fabrication process could be easily expanded from 1D to 2D structures. In this study, we conduct experimental evaluations on both 1D and 2D structures, showcasing its exceptional noise and vibration attenuation capabilities compared to conventional damping treatments. Our approach offers practical potential for the development of lightweight materials suitable for noise and vibration control in confined spaces.

Tunable wideband terahertz absorber based on single-layer patterned graphene

In this study, we propose and validate a broadband terahertz perfect absorber. The absorber has a simple structure, which consists of a gold (Au) substrate, a TOPAS dielectric layer and a patterned graphene layer. By the simulations, a broad absorption band can be obtained with a high absorption above 90% between 3.31 THz and 7.15 THz, and the relative bandwidth reaches 73.4%. Meanwhile, the absorption higher than 99% is between 3.81 THz and 6.6 THz with a relative bandwidth of 53.6%. The mechanism of the surface excited plasma (SPP) and electromagnetic dipole resonance are responsible for its almost perfect broadband absorption. By changing the Fermi energy level of the graphene layer, the flexible broadband absorption spectra can be acquired. By varying the geometrical parameters of the structure, a wider spectral range of absorption wavelengths can be realized. For both TE and TM polarization, the absorption can remain above 90% over a wide range of incidence angles. Due to the independent tunability and high absorption of the proposed device, it has great potential applications in terahertz imaging, smart absorption, detectors and communications.

Ultra-broadband and thin switchable multifunctional metamaterial for terahertz wave

An ultra-broadband thin multi-functional and switchable metamaterial is examined in the terahertz (THz) regime. The proposed design achieved high polarization conversion efficiency and can be switched from a polarization converter to an absorber using the phase change transitioning of vanadium dioxide (VO2). The linear polarization conversion is achieved from 6.0 THz to 15.0 THz, achieving a bandwidth of 9.0 THz, and the absorption is realized from 5.0 THz to 16.0 THz with a bandwidth of 11.0 THz. These broadband characteristics were achieved by a simple metamaterial design incorporating a few layers. The relative bandwidth was 85% for the polarization conversion and 105% for the absorption. Moreover, the angular stability of the designed structure is impressive for various incident angles from 0° to 45°. The proposed switchable design has the potential to contribute to the development of tunable polarization rotating devices, on/off switching LPC devices, which have wide application potentials in THz detection, sensing, adaptive optics, and communications.

Electromagnetic transmission of two-dimensional inhomogeneous plasma photonic crystal

A 2D tunable plasma photonic crystal (PPC) was constructed and implemented experimentally over a frequency range of 1 GHz–12 GHz within the electromagnetic spectrum. The PPC was simulated using an inhomogeneous model of a plasma tube based on microwave diagnostics and numerical simulations. The simulation results were found to be in good agreement with the experimental results. The data indicates that for TM polarization, localized plasmons will be excited at various positions within the tube, which does not rely on an interface with the medium, resulting in a broad forbidden band due to plasma inhomogeneity. The bandwidth of this band is consistent with the plasma frequency range. Furthermore, a lattice resonance band is observed, which is related to the incident angle. The cutoff effect of inhomogeneous PPC for TE polarization can be predicted by averaging the plasma parameters. The structure or plasma parameters can be adjusted to tune all the bands mentioned above. These findings can be used as a reference for applications in communication and microwave devices, and could potentially be utilized as a diagnostic tool for plasma parameters.

Transport properties through alternating borophene and graphene superlattices

The electronic transport properties of two junctions (BGB, GBG) made of borophene (B) and graphene (G) are investigated. Using the transfer matrix method with Chebyshev polynomials, we have studied single and multiple barriers in a superlattice configuration. We showed that a single barrier exhibits remarkable tilted transport properties, with perfect transmission observed for both junctions under normal incidence. We found that robust superlattice transmission is maintained for multiple barriers, particularly in the BGB junction. It turns out that by varying the incident energy, many gaps appear in the transmission probability. The number, width, and position of these transmission gaps can be manipulated by adjusting the number of cells, incident angle, and barrier characteristics. For diffuse transport, we observed considerable variations in transmission probability, conductance and the Fano factor, highlighting the sensitivity of these junctions to the physical parameters. We showed different behaviors between BGB and GBG junctions, particularly with respect to the response of conductance and Fano factor when barrier height varies. For ballistic transport, we have seen that the minimum scaled conductance is related to the maximum Fano factor, demonstrating their control under specific conditions of the physical parameters. Analysis of the length ratio (geometric factor) revealed some remarkable patterns, where scaled conductance and the Fano factor converged to certain values as the ratio approached infinity.