Photonic wire bonding is demonstrated to enable highly efficient coupling between multicore fibers and planar silicon photonic circuits. The technique relies on in-situ fabrication of ...three-dimensional interconnect waveguides between the fiber facet and tapered silicon-on-insulator waveguides. Photonic wire bonding can easily compensate inaccuracies of core placement in the fiber cross-section, does not require active alignment, and is well suited for automated fabrication. We report on the design, on fabrication, and on characterization of photonic wire bonds. In a proof-of-principle experiment, a four-core fiber is coupled to a silicon photonic chip, leading to measured coupling losses as small as 1.7 dB.
A solar-pumped laser (SPL) that converts sunlight directly into a coherent and intense laser beam generally requires a large concentrating lens and precise solar tracking, thereby limiting its ...potential utility. Here, we demonstrate a fully-planar SPL without a lens or solar tracking. A Nd3+-doped silica fiber is coiled into a cylindrical chamber filled with a sensitizer solution, which acts as a luminescent solar collector. The body of the chamber is highly reflective while the top window is a dichroic mirror that transmits incoming sunlight and traps the fluorescence emitted by the sensitizer. The laser-oscillation threshold was reached at a natural sunlight illumination of 60% on the top window. Calculations indicated that a solar-to-laser power-conversion efficiency could eventually reach 8%. Such an SPL has potential applications in long-term renewable-energy storage or decentralised power supplies for electric vehicles and Internet-of-Things devices.Solar-pumped laser systems are attractive for applications including hydrogen generation and space propulsion, but current technologies are cumbersome and rely on accurate tracking of the sun’s light. Here, lasing is achieved using a planar, luminescent solar collector removing the need for lenses or tracking.
Unclonable anticounterfeiting labels can be based on micrometer‐scale randomness created by stochastic processes like the distribution of luminescent microparticles in a transparent layer. Adding a ...microlens array to the layer can simplify the hardware needed for authentication in that magnification is no longer required. The bright point‐pattern generated under light‐emitting diode illumination can be captured by a standard digital camera. Shifting the angle of incidence (AOI) relocates the microlens foci changing the bright point‐pattern. This provides unclonability, as several distinct bright point patterns at different AOI can be required for authentication. However, it also imposes technical requirements for the authentication setup in terms of the tolerance with which the AOI must be controlled. Herein, the AOI tolerance, the deviation of angle between reference and test image for which sufficiently similar bright point patterns are recorded that they are considered matching by the authentication algorithm, is investigated. Using microlens arrays with a focal length of 550 μm, the average size of the phosphor particle was varied from 9 ± 1 to 32.5 ± 2 μm, resulting in a relaxation of tolerance from 0.8° to 3.6°. Methods to further increase the AOI tolerance and facilitate the practical implementation of these labels are discussed.
Unclonable anticounterfeiting labels creating patterns of bright emission points can be made from a microlens array and a layer doped with microparticle phosphors. The emission pattern depends on the illumination's incidence angle. Herein, the range of angular offsets that a test image can be taken with respect to a reference image is extended.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Optical gain of 8.3 km−1 is obtained in a neodymium‐doped silica fiber under simulated sunlight (intensity = 2.1 kW m−2). The fiber gain medium (length = 50 m) is coiled and attached to a solid‐state ...luminescent solar concentrator (LSC) disk (diameter = 180 mm). The disk/fiber unit is placed in a cavity comprising highly reflective (HRM) and dichroic (DM) mirrors to increase the photon confinement by a factor of 2.2 compared with a liquid LSC (also employing HRM/DM). The enhancement is mainly due to the air gap between HRM/DM and LSC, which affords total internal reflection (TIR) in the solid‐state LSC and an ideal boundary condition for the multilayer mirrors. The numerical calculations indicate that an additional 2.2‐times enhancement is achievable with a side wall exhibiting 90% diffuse reflection. This has been experimentally confirmed (1.9‐times optical‐gain enhancement is realized by adding a polytetrafluoroethylene side‐wall reflector). Overall, the solid‐state LSC‐based solar‐pumped laser (SPL) comprising reflective side walls exhibits a gain factor of 4.2, which is superior to its liquid‐state predecessor. Further improvements employing a solid‐state LSC design and fiber optimization will facilitate the market penetration of SPLs.
An improved solar‐pumped laser design is demonstrated. It comprises of a solid‐state luminescent solar concentrator sandwiched by a dichroic mirror and a highly reflective mirror. An optical gain of 8.3 km−1 is observed by exploiting both total internal reflection and multilayer reflectors. The observed gain is 4.2 times larger than our liquid‐state predecessor which recently demonstrated lasing.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Air‐stable inorganic cesium lead iodide (CsPbI3) perovskite thin films with a bandgap of 1.7 eV are a promising candidate for tandem cell solar cells, comprising a perovskite top cell with a ...crystalline silicon bottom cell. The device design and simulations are important to develop high‐efficiency photovoltaic devices. However, knowledge of complex optical constants of the CsPbI3 thin films is mandatory to complement such tasks. Herein, air‐stable inorganic CsPbI3 perovskite thin films are prepared using one‐step synthesis through a spin‐coating method. Variable angle spectroscopic ellipsometry (VASE) is then conducted at five angles (43.9°, 48.9°, 53.9°, 58.9°, and 63.9°) to obtain ellipsometric data (Ψ and Δ). The thickness nonuniformity model of the perovskite thin film combined with an effective medium approximation for describing rough surface is adopted to achieve excellent fitting. The complex optical constants of the CsPbI3 thin film are experimentally obtained in the wavelength range of 300–1200 nm. The present results open the door for design and simulations on high‐efficiency CsPbI3/c‐Si tandem solar cells.
Air‐stable all‐inorganic CsPbI3 perovskite thin films are prepared. Variable angle spectroscopic ellipsometry is conducted at five angles to obtain ellipsometric data (Ψ and Δ). Through model construction, the complex optical constants of the CsPbI3 thin film are experimentally obtained, which opens the door for design and simulations on high‐efficiency CsPbI3/c‐Si tandem solar cells.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The soiling of photovoltaic (PV) modules can significantly reduce their energy yield unless a mitigation strategy is employed. One solution investigated in this work involves the implementation of a ...passive self-cleaning superhydrophobic top cover. To this end, superhydrophobicity was induced by hot-embossing random microtextures on a highly transmissive and photostable fluorinated ethylene propylene (FEP) film. The impact of fabrication parameters (hot-embossing force and temperature) on achieving high contact angles (> 150°) and low roll-off angles (< 10°), which characterizes a surface as superhydrophobic, were investigated. It was found that a minimum threshold force of at least 15 kN and 5 kN must be used to achieve superhydrophobicity for processing temperatures of 270 °C and 280 °C respectively. Meanwhile at the highest investigated temperature of 290 °C, any force within the investigated range of 500 N to 50 kN suffices. The best fabrication parameters were identified (5 kN at 280 °C), resulting in a contact angle of 156 ± 1° and a roll-off angle of 8 ± 3°. When incorporated into a silicon PV mini-module, the addition of the textured FEP film enhances the short circuit current density (JSC) by 1.1%. Moreover, the self-cleaning properties of the textured FEP films result in a recovery ratio of 93.6% (in terms of JSC), which is significantly greater than that of the reference glass encapsulated PV mini-module (61.1%).
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•Random microtextures produce highly transmissive and superhydrophobic FEP surface.•Minimum threshold force to achieve superhydrophobicity identified (5 kN).•Easier to obtain superhydrophobicity at higher fabrication temperatures.•Relative 1.1% enhancement of power conversion efficiency of PV modules.•Self-cleaning recovery of 93.6% in terms of JSC achieved with best case sample.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We have developed a fully planar solar-pumped fiber laser using a solid-state luminescent solar collector (LSC). This laser does not use any focusing device, such as a lens or mirror; thus, it can ...lase without tracking the sun. Our developed device with an aperture of 30 cm emits 15 mW, corresponding to an optical-to-optical conversion efficiency of 0.023% and a collection efficiency of 0.21 W/m
2
. A 12-fold improvement over a previously developed liquid LSC is achieved by combining the total internal reflection of the solid-state LSC with dielectric multilayer mirrors. The observed laser power is in good agreement with that predicted via numerical simulation, demonstrating the effectiveness of our proposed method.
Superhydrophobic self-cleaning covers, exhibiting small roll-off angles of water droplets, mitigate the soiling of photovoltaic (PV) modules. In this work, microcone-textured fluorinated ethylene ...propylene (FEP) covers attached to the front side of PV modules offer improved performance via dual functionality, namely via self-cleaning and reduced parasitic reflection losses. The aspect ratio of the FEP microcone-textures was investigated in view of both functionalities. The best performing microcone-textured cover (aspect ratio of 0.7) demonstrated a significant enhancement in short-circuit current density (JSC) of 3.1% relative when applied to Cu(In,Ga)Se2 solar cells. Furthermore, compared to a planar FEP layer, the microcone-textures showed superior self-cleaning capability when tested using different soil types. Microcone-textured FEP recovered 100% and 65.8% of photocurrent generated when soiled with sea sand and Arizona test dust, respectively. We also present robust microcone-textured FEP covers such that superhydrophobicity was still achieved even with truncated microcones.
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•Superhydrophobicity achieved with microcone-textured FEP for all aspect ratios.•Optimum aspect ratio of 0.7 enhances both self-cleaning and light harvesting.•Significant self-cleaning enhancement observed for two distinct soil types.•Relative 2.9% power conversion efficiency enhancement for CIGS mini-modules.•Even imperfect microcone-textures in FEP achieved superhydrophobicity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
All-inorganic perovskites exhibit interesting properties and unprecedented stability compared to organic-inorganic hybrid lead halide perovskites. This work focuses on depositing and characterizing ...cesium lead bromide (CsPbBr
) thin films and determining their complex optical constants, which is a key requirement for photovoltaic device design. CsPbBr
thin films are synthesized via the solution method followed by a hot-embossing step to reduce surface roughness. Variable angle spectroscopic ellipsometry measurements are then conducted at three angles (45°, 55°, and 65°) to obtain the ellipsometric parameters psi (Ψ) and delta (Δ). For the present model, bulk planar CsPbBr
layer is described by a one-dimensional graded index model combined with the mixture of one Tauc-Lorentz oscillator and two Gaussian oscillators, while an effective medium approximation with 50% air void is adopted to describe surface roughness layer. The experimental complex optical constants are finally determined in the wavelength range of 300 to 1100 nm. Furthermore, as a design example demonstration, the simulations of single-junction CsPbBr
solar cells are conducted via the finite-difference time-domain method to investigate the properties of light absorption and photocurrent density.
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