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Developing versatile systems that can concurrently achieve energy saving and energy generation is critical to accelerate carbon neutrality. However, challenges on designing highly effective, large scale, and multifunctional photonic film hinder the concurrent combination of passive daytime radiative cooling (PDRC) and utilization of sustainable clean energies. Herein, a versatile scalable photonic film (Ecoflex@h-BN) with washable property and excellent mechanical stability is developed by combining the excellent scattering efficiency of the hexagonal boron nitride (h-BN) nanoplates with the high infrared emissivity and ideal triboelectric negative property of the Ecoflex matrix. Strikingly, sufficiently high solar reflectance (0.92) and ideal emissivity (0.97) endow the Ecoflex@h-BN film with subambient cooling effect of ≈9.5 °C at midday during the continuous outdoor measurements. In addition, the PDRC Ecoflex@h-BN film-based triboelectric nanogenerator (PDRC-TENG) exhibits a maximum peak power density of 0.5 W m-2 . By reasonable structure design, the PDRC-TENG accomplishes effective wind energy harvesting and can successfully drive the electronic device. Meanwhile, an on-skin PDRC-TENG is fabricated to harvest human motion energy and monitor moving states. This research provides a novel design of a multifunctional PDRC photonic film, and offers a versatile strategy to realize concurrent PDRC and sustainable energies harvesting.
RESUMO
Passive daytime radiative cooling (PDRC) materials with sustainable energy harvesting capability is critical to concurrently reduce traditional cooling energy utilized for thermal comfort and transfer natural clean energies into electricity. Herein, a versatile photonic film (Ecoflex@BTO@UAFL) based on a novel fluorescent luminescence color passive radiative cooling with triboelectric and piezoelectric effect is developed by filling the dielectric BaTiO3 (BTO) nanoparticles and ultraviolet absorption fluorescent luminescence (UAFL) powder into the elastic Ecoflex matrix. Test results demonstrate that the Ecoflex@BTO@UAFL photonic film exhibits a maximum passive radiative cooling effect of â½10.1 °C in the daytime. Meanwhile, its average temperature drop in the daytime is ~4.48 °C, which is 0.91 °C higher than that of the Ecoflex@BTO photonic film (3.56 °C) due to the addition of UAFL material. Owing to the high dielectric constant and piezoelectric effect of BTO nanoparticles, the maximum power density (0.53 W m-2, 1 Hz @ 10 N) of the Ecoflex@BTO photonic film-based hybrid nanogenerator is promoted by 70.9% compared to the Ecoflex film-based TENG. This work provides an ingenious strategy for combining PDRC effects with triboelectric and piezoelectric properties, which can spontaneously achieve thermal comfort and energy conservation, offering a new insight into multifunctional energy saving.
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Lasers play a significant role in optical communication, medical, and scientific research, owing to their high brightness and high coherence. However, the high spatial coherence will lead to specific challenges, such as speckle noise in imaging and wavefront distortion during propagation through scattering media. Here, a continuous-wave (cw) degenerate cavity laser (DCL) with low spatial coherence is demonstrated with efficient suppression of the thermal lensing effect from the gain crystal. Experimentally, a cw degenerate laser output with about 2000 transverse modes corresponding to a speckle contrast of about 0.0224 is achieved. This laser can be used for speckle reduction and is robust against atmospheric turbulence, which may find applications in the field of laser imaging technology and illumination.
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In recent years, wide field-of-view imaging technology based on a metasurface has been widely applied. However, works on the reported sub-diffraction metalens with a wide field-of-view indicate that multiple structures are essential to effectively eliminate aberrations, which results in a heavy device thickness and weakens the advantage of an ultra-thin metasurface. To solve this problem, according to the super-oscillation theory and the translational symmetry of quadratic phase, as well as the principle of virtual aperture diaphragm based on wave vector filter, this Letter demonstrates a sub-diffraction metalens combined with a single quadratic metalens and a wave vector filter. Our design not only realizes the super-resolution effects of 0.74 to 0.75 times the diffraction limit in the wide field-of-view of nearly 180° for the first time to our knowledge but also compresses the device thickness to the subwavelength order in principle. The proposed ultra-thin sub-diffraction metalens with a wide field-of-view is expected to be applied in the fields of super-resolution fast scanning imaging, information detection, small target recognition, and so on.
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This paper proposes and demonstrates a flexible long-wave infrared snapshot multispectral imaging system consisting of a simple re-imaging system and a pixel-level spectral filter array. A six-band multispectral image in the spectral range of 8-12â µm with full width at half maximum of about 0.7â µm each band is acquired in the experiment. The pixel-level multispectral filter array is placed at the primary imaging plane of the re-imaging system instead of directly encapsulated on the detector chip, which diminishes the complexity of pixel-level chip packaging. Furthermore, the proposed method possesses the merit of flexible functions switching between multispectral imaging and intensity imaging by plugging and unplugging the pixel-level spectral filter array. Our approach could be viable for various practical long-wave infrared detection applications.
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In this paper, we demonstrated a miniaturized diffractive/refractive hybrid system based on a diffractive optical element and three refractive lenses to achieve solar-blind ultraviolet imaging within a range of 240-280â nm. We experimentally demonstrate the optical system has both outstanding resolution and excellent imaging capability. The experiments demonstrate that the system could distinguish the smallest line pair with a width of 16.7â µm. The modulation transfer function (MTF) at the target maximum frequency (77 lines pair/mm) is great than 0.76. The strategy provides significant guidance for the mass production of solar-blind ultraviolet imaging systems towards miniaturization and lightweight.
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Phase-gradient metasurfaces are two-dimensional (2D) optical elements that can manipulate light by imposing local, space-variant phase changes on an incident electromagnetic wave. These metasurfaces hold the potential and the promise to revolutionize photonics by providing ultrathin alternatives for a wide range of common optical elements such as bulky refractive optics, waveplates, polarizers, and axicons. However, the fabrication of state-of-the-art metasurfaces typically requires some time-consuming, expensive, and possibly hazardous processing steps. To overcome these limitations on conventional metasurface fabrication, a facile methodology to produce phase-gradient metasurfaces through one-step UV-curable resin printing is developed by our research group. The method dramatically reduces the required processing time and cost, as well as eliminates safety hazards. As a proof-of-concept, the advantages of the method are clearly demonstrated via a rapid reproduction of high-performance metalenses based on the Pancharatnam-Berry phase gradient concept in the visible spectrum.
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Free space optical (FSO) communication has gained widespread attention due to its advantages, including high confidentiality, high communication capacity, and no limitation of spectrum. One of the great challenges in FSO communication is the transmission performance degradation in atmospheric turbulence channel due to wavefront distortion and scintillation. Here, we proposed and experimentally demonstrated a 120 Gbit/s vector beam multiplexed coherent optical communication system with turbulence-resilient capacity. Four multiplexed vector beams, each carrying a 30 Gbit/s quadrature phase-shift keying signal, propagate through different turbulence conditions. The influence of turbulence channel on the vector beam impairments is experimentally investigated. Under the weaker turbulence conditions, the system bit error rates are below the forward error correction threshold of 3.8 × 10-3. In comparison with the Gaussian mode, the communication interruption probability of the vector beams system decreases from 36% to 12%-18% under stronger turbulence conditions.
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For the first time, to the best of our knowledge, we experimentally demonstrate a high-speed free-space secure optical communication system based on all-optical chaos modulation. The effect of atmospheric turbulence on optical chaos synchronization is experimentally investigated via a hot air convection atmospheric turbulence simulator. It is shown that, even under moderately strong turbulent conditions, high-quality chaos synchronization could be obtained by increasing the transmission power. Moreover, a secure encryption transmission experiment using a high bias current induced chaotic carrier for 8-Gbit/s on-off-keying data over a â¼10-m free-space optical link is successfully demonstrated, with a bit-error rate below the FEC threshold of 3.8 × 10-3. This work favorably shows the feasibility of optical chaotic encryption for the free-space optical transmission system.
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We propose a dual-band achromatic focusing metasurface based on polarization multiplexing and dispersion engineering. An anisotropic resonant phase meta-atom is designed to realize independent nonlinear phase manipulation along the orthogonal directions. Achromatic focusing metasurface and broadband reflectarray antenna are further constructed in the microwave region with a computer-assisted particle swarm optimization algorithm. The standard deviation of focus offset at 11-16 GHz (for x-polarization) and 18-24 GHz (for y-polarization) are compressed to 19.83% and 16.60% of the dispersive metasurface, respectively. The radiation gains of the reflectarray antenna increase by an average of 19.49 dB and 15.08 dB in the broadband region compared with the bare standard rectangle waveguides. Furthermore, such an achromatic metasurface can be utilized to realize different functions with polarization selectivity and applied to other frequency ranges, which holds great promise in integrated optics.
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In this paper, all-metallic reflective metasurfaces comprising S-shape streamline structures are proposed to achieve the photonic spin-Hall effect with average cross-polarization conversion efficiency exceeding â¼84% in the range of 8-14 µm. By comparing with all-metallic nanobricks, it is demonstrated that the electric field coupling could be enhanced by constructing a similar split ring resonator between adjacent unit elements to further improve its efficiency and bandwidth. As a proof of concept, the photonic spin Hall effect and spin-to-orbit angular momentum conversion could be observed by two metadevices with the maximum diffraction efficiency of â¼95.7%. Such an all-metallic configuration may provide a platform for various high-efficiency electromagnetic components, catenary optics, and practical applications.
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Beam scanning based on metasurfaces is widely discussed in recent years owing to its high integration, lightweight, and low cost. However, most of the reported beam scanning metasurfaces operate in either transmission or reflection mode. Here, we propose a full-space beam scanning metasurface based on transmission reflection switchable meta-atom and the quadratic phase distribution. As a validation, a metasurface array with 400 units (20 × 20) was experimentally demonstrated. Beam scanning of ± 35 ° was achieved in both transmission mode and reflection mode. A larger scanning angle (± 45 °) was further verified simulatively with a 900-units (30 × 30) array. The method provides an avenue for expanding the space of electromagnetic wave manipulation and may have great potential in wireless communication and radar detection.
RESUMO
Visible-infrared compatible camouflage is significant to enhance the equipment survivability through counteracting the modern detecting and surveillance systems. However, there are still great challenges in simultaneously achieving multispectral camouflage with high transmittance in visible, low emissivity in the atmospheric windows and high emissivity in the non-atmospheric window, which can be attributed to the mutual influence and restriction within these characteristics. Here, we proposed an optically transparent infrared selective emitter (OTISE) composed of three Ag-ZnO-Ag disk sub-cells with anti-reflection layers, which can synchronously improve the visible transmittance and widen absorption bandwidth in the non-atmospheric window by enhancing and merging resonance response of multi-resonators. Test results reveal that low emissivity in infrared atmospheric windows, high emissivity in the 5-8 µm non-atmospheric window and high optical transparency have been obtained. In addition, the radiative flux of OTISE in 3-5 µm and 8-14 µm are respectively 34.2% and 9.3% of that of blackbody and the energy dissipation of OTISE is 117% of that of chromium film. Meanwhile, it keeps good optical transparency due to the ultrathin Ag film. This work provides a novel strategy to design the optically transparent selective emissive materials, implying a promising application potential in visible and infrared camouflage technology.
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Active wave manipulation by ultracompact meta-devices is highly embraced in recent years, but a major concern still exists due to the lack of functional reconfigurability. Moreover, the phase or amplitude discontinuities introduced by collective response of discrete meta-atoms make current meta-devices far from practical applications. Here, we demonstrate actively tunable wavefront control with high-efficiency by combining catenary-based meta-atoms for intrinsic continuous phase regulation with the chalcogenide phase change material (PCM) of Ge2Sb2Te5. First, switchable beam deflection is demonstrated in a wide mid-IR range between 8 µm and 9.5 µm with 'on' and 'off' states for beam steering between anomalous and normal specular reflections. Second, a switchable meta-axicon for zero order Bessel beam generation is demonstrated with full width at half maximum (FWHM) as small as â¼0.41 λ (λ = 12 µm). As a result, our scheme for active and continuous phase control potentially paves an avenue to construct active photonic devices especially for applications where large contrast ratio is highly desirable, such as optoelectronic integration, wavefront engineering and so on.
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In this work, we propose dynamic holography based on metasurfaces combining spatial channel multiplexing and polarization multiplexing. In this design, spatial channels can provide up to 3N holographic frames, which not only increase the possibility of dynamic control but also increase the privacy of the holographic display. This design is also sensitive to polarization, so it further expands the spatial channel capacity. For the left and right circular polarization incident light, there are different dynamic pixel schemes. Therefore, this approach holds promise in the holographic display, optical storage, optics communication, optical encryption, and information processing.
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Conventional achromatic optical systems are matured to achieve effective chromatic aberration correction and diffraction-limited resolution by the multiple bulky lenses. The emergence of the super-oscillation phenomenon provides an effective method for non-invasive far-field super-resolution imaging. Nevertheless, most super-oscillatory lenses are significantly restricted by the chromatic aberration due to the reliance on delicate interference; on the other hand, most achromatic lenses cannot break the diffraction limit. In this article, a single-layer broadband achromatic metasurface comprising sub-wavelength anisotropic nanostructures has been proposed to achieve sub-diffraction focusing with a focal length of f=60 µm and a diameter of 20 µm in the visible ranging from 400 nm to 700 nm, which are capable of generating sub-diffraction focal spots under the left-handed circularly polarized incident light with arbitrary wavelength in the working bandwidth at the same focal plane. This method may find promising potentials in various applications such as super-resolution color imaging, light field cameras, and machine vision.
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We investigate the topology optimization of geometric phase metasurfaces for wide-angle and high-efficiency deflection, where adjoint-based multi-object optimization approach is adopted to improve the absolute efficiency while maintaining the polarization conversion characteristic of geometric phase metasurfaces. We show that, for the initially discrete geometric phase metasurfaces with different materials and working wavelengths, the topology shapes gradually evolve from discrete structures to quasi-continuous arrangements with the increment of optimization iteration operations. More importantly, the finally optimized metasurfaces manifest as catenary-like structure, providing significant improvements of absolute efficiency. Furthermore, for the initial structure with catenary distribution, the corresponding optimized metasurface also has a catenary-like topology shape. Our results on the topology-optimized geometric phase metasurfaces reveal that, from the perspective of numerical optimization, the continuous catenary metasurfaces is superior to the discrete geometric phase metasurfaces.
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Based on the delicate interference behavior of light in the far field, the optical super-oscillatory phenomenon has been successfully applied in non-invasive sub-diffraction focusing and super-resolution imaging in recent years. However, the optical super-oscillatory field is particularly sensitive to the change of incident angle, leading to a limited field of view for super-resolution imaging. In this paper, a super-oscillatory metasurface doublet is proposed to achieve far-field sub-diffraction focusing with an incident angle of up to 25°. The constructed doublet, consisting of high-aspect-ratio rectangular nanopillars with high efficiency, is further demonstrated through a full-wave simulation, and the numerical results indicate that the sub-diffraction foci with about 0.75 times of the diffraction limit is achieved for different incident angles. The proposed super-oscillatory metasurface doublet may find intriguing applications in label-free super-resolution microscopy and optical precise fabrication.
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Pancharatnam-Berry geometric phase has attracted enormous interest in subwavelength optics and electromagnetics during the past several decades. Traditional theory predicts that the geometric phase is equal to twice the rotation angle of anisotropic elements. Here, we show that high-order geometric phases equal to multiple times the rotation angle could be achieved by meta-atoms with highfold rotational symmetries. As a proof of concept, the broadband angular spin Hall effect of light and optical vortices is experimentally demonstrated by using plasmonic metasurfaces consisting of space-variant nanoapertures with C2, C3, and C5 rotational symmetries. The results provide a fundamentally new understanding of the geometric phase as well as light-matter interaction in nanophotonics.
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In this paper, a highly integrated array-based imaging system, composed of a lens array and a metasurface array, is proposed to achieve multispectral real-time imaging within a wide range of 400-1100â nm numerically. Each channel has an achromatic bandwidth of 50 nm and an aperture of about 5 mm, with the system average efficiency reaching over 91%. It breaks the restrictions of cumbersome volumes and limited materials that deteriorate the performance of conventional systems, facilitating miniaturization and integration. Moreover, the design method is also suitable for other spectral bands, widening applications of metasurfaces in multispectral imaging.