Optical Efficiency Research Articles

Two-dimensional pnictogen carbides and their Janus structures: Potential on visible-light photocatalytic water splitting for hydrogen production

This study explored eight novel and highly stable monolayer configurations: C3X2 (X = N, P, As, Sb, and Bi) and C3XY (X = P and As, YAs and Sb) by analyzing their electronic, optical, and photocatalytic properties based on first-principles density functional theory. The findings indicated that the C3X2 monolayers, except for C3Bi2, exhibit indirect band gap semiconductor properties, and their band gaps are 1.497, 1.862, 2.272, 1.448, and 1.561 eV, respectively. Notably, only C3P2 and C3As2 fulfilled the prerequisites for photocatalytic water splitting, boast high electron mobility (up to ∼103 cm2/Vs), strong absorption in the visible light range, and high solar-to-hydrogen (STH) efficiency (30.16% for C3P2 and 23.05% for C3As2). Moreover, the Janus C3PAs, C3PSb, and C3AsSb monolayers exhibited indirect band gaps ranging from 1.616 to 2.070 eV and satisfied the band structure criteria for photocatalytic water splitting. These three Janus monolayers outperformed C3X2 in terms of optical absorption, carrier mobility, and STH efficiency owing to their inherent electric fields. The STH efficiency of C3PSb and C3AsSb reach 31.26% and 29.17%, respectively, with electron mobility reaching up to 4642.01 and 11902.64 cm2/Vs, respectively, indicating their exceptional potential for photocatalytic water splitting.

Three-layer polarisation volume grating with enhanced diffraction efficiency and FOV in AR and VR applications

ABSTRACT In the rapidly evolving fields of Augmented Reality (AR) and Virtual Reality (VR), achieving high diffraction efficiency and a wide field of view (FOV) is critical for enhancing visual experience. This paper presents a three-layer Polarisation Volume Grating (TL-PVG) structure designed to address the limitations of single-layer PVGs in AR/VR applications. By stacking multiple PVG layers with different tilt angles, TL-PVG achieves an expanded angular bandwidth and improved diffraction efficiency, enabling brighter and more immersive displays. The proposed TL-PVG structure incorporates polarisation multiplexing to optimise the optical diffraction efficiency by approximately 75%, thereby enhancing image brightness and sharpness. The experimental results demonstrate that TL-PVG significantly outperforms traditional single-layer PVGs, offering a promising solution for waveguide elements in next-generation AR/VR displays. This study provides a comprehensive analysis of the fabrication process, optical properties, and applications of TL-PVGs, highlighting their potential to revolutionise the AR/VR technology.

Effect of manufacturing tolerances on Micro-CPV assemblies: A quantitative approach based on statistical modeling

In micro-concentrator photovoltaics (micro-CPV) minimized components as cells (<1 × 1 mm2) and lenses are used, promising significant cost reductions through parallel manufacturing and reduced material volumes. However, tolerances, such as deviations from nominal size, geometry or position, impact module performance, especially for non-ideal alignment towards the sun. To study the interplay of different, independent tolerances and their effects on current generation, a comprehensive parameter study is practically not feasible, because of the vast number of possible combinations. In this work, we introduce a novel method for assessing tolerances by employing a Monte-Carlo approach to randomly select and combine tolerances in a cell-lens unit. It allows to identify relevant tolerances and quantitatively assess their influence on module performance, namely optical efficiency, and photocurrent as function of angle of incidence and, thus, acceptance angle. We apply the model to a micro-CPV module developed at Fraunhofer ISE and use tolerance distributions based on measurements. We find that the most crucial parameter is the position of the secondary optical element. Given the measured tolerance distributions, the acceptance angles for 90 % of the cases are above 0.5° for 10 % current loss. The developed approach is a crucial tool for identifying and assessing critical tolerances within a manufacturing line, facilitating techno-economic optimization of design and manufacturing processes.

Enhanced photocatalytic performance of (Mg, Cu) Dual-Doped ZnS nanosheets for Solar-Driven water treatment and embedded with PVA polymer membrane for reusability

Photocatalysis uses semiconductor materials to solar energy effectively purify to water by eliminating pollutants. Organic Dye degradation serves as a standard to assess the photocatalytic effects of the materials. In this study Mg, Cu dual-doped ZnS nanosheets were synthesized using the coprecipitation method. The impact of the concentration on the structural, morphology, optical, and degradation efficiency was investigated with XRD, XPS, TEM with EDAX, and UV spectroscopy. The pure ZnS and Zn0.98-xCu0.02MgxS (x = 0, 0.01, 0.02) (ZCM1, ZCM2, ZCM3, and ZCM4) nanosheets, exhibited cubic structure with high phase purity. The average crystalline size was calculated as 1.66, 1.60, 1.45, and 1.47 nm for the ZCM1, ZCM2, ZCM3, and ZCM4 nanosheets, respectively. TEM analysis revealed the presence of crumpled nanosheets. The bandgap of the ZCM1, ZCM2, ZCM3, and ZCM4 nanosheets were 3.99, 3.78, 4.03, and 4.09 eV respectively. This study investigated the photocatalytic activity of crystal violet dye when exposed to natural sunlight irradiation. Notably, ZCM3 nanosheets exhibited a high degradation rate of 99 % over 120 min under sunlight. Furthermore, the proposed dye degradation mechanism, effect of dosage, effect of dye variation, reusability, scavenging activity, and hemolytic activity were comprehensively discussed. The nanosheets embedded with the Polyvinyl alcohol (PVA) polymer membrane for reusability.

Integrated sensor chip of a resonant cavity light emitter and photon detector for wearable optical medicine

This work presents an integrated chip of a resonant cavity light emitter and photon detector (RCLEPD) to address the requirements of wearable optical medical devices for compact size, high efficiency, and interference resistance sensors. The optical radiation pattern and light extraction efficiency of the resonant cavity light emitting diode (RCLED) as well as the optical absorption spectrum of the resonant cavity enhanced photon detector (RCEPD) are theoretically simulated. Additionally, the wavelength selectivity of the RCEPD absorption spectrum is analyzed. Material epitaxial growth of RCLEPD was performed using metal-organic chemical vapor deposition (MOCVD), and an integrated sensing chip with an area of 2 × 2 mm2 was fabricated. Experimental results demonstrate that RCLED achieves a maximum external quantum efficiency of 10.206%, consistent with the simulation results, while maintaining a peak wavelength at 677.5 nm within a current range of 0-20 mA. Furthermore, the RCEPD exhibits a peak response wavelength at 678 nm, matching that of the RCLED. Utilizing RCLEPD as the sensor, photoplethysmography (PPG) signals are collected from the human wrist under different RCLED driving currents resulting in an average period of 977 ms which aligns with a human pulse frequency of 61 beats/min. With further processing techniques applied to PPG signals, RCLEPD is expected to be used as a sensor in wearable blood pressure and glucose monitoring devices.

Design and Performance Characteristics of Single-Axis Tracking Dual Confocal Low-Magnification Parabolic Trough CPV system

With the rapid increase of PV module utilization, the environmental pollution associated with waste photovoltaic (PV) module and its recycling is of concern. This paper proposes a concentrating photovoltaic (CPV) system to reduce the use of PV module. The cross-confocal method is employed for the concentrator to eliminate central dark streaks. In optical simulation, a theoretical uniformity index of 0.0466 and a theoretical optical efficiency of 89.87% were achieved. When the distance between the rotational axis and the center of gravity is less than 125.8mm, the system can withstand winds of 20.4m/s. The temperature range of the PV, obtained from finite element analysis, is from 295.71 K to 363.13 K. With the requirements of the relative optical efficiency of over 90% and the uniformity index of less 0.5, the system has a dimensional translation tolerance of approximately ±10mm, a dimensional rotation tolerance of about 5°, and a tracking angle tolerance of about 1°. The actual daily average output current of this system has increased by 100.91%. The ratio between the increase ratio of output current and the theoretical concentration ratio is 83.4%. The system demonstrates excellent optical performance and system tolerance.

Multifunctional computational fluorescence self-interference holographic microscopy

Fluorescence microscopy is crucial in various fields such as biology, medicine, and life sciences. Fluorescence self-interference holographic microscopy has great potential in bio-imaging owing to its unique wavefront coding characteristics; thus, it can be employed as three-dimensional (3D) scanning-free super-resolution microscopy. However, the available approaches are limited to low optical efficiency, complex optical setups, and single imaging functions. The geometric phase lens can efficiently manipulate the optical field’s amplitude, phase, and polarization. Inspired by geometric phase and self-interference holography, a self-interference fluorescent holographic microscope-based geometric phase lens is proposed. This system allows for wide-field, 3D fluorescence holographic imaging, and edge-enhancement from the reconstruction of only one complex-valued hologram. Experiments demonstrate the effectiveness of our method in imaging biological samples, with improved resolution and signal-to-noise ratio. Furthermore, its simplicity and convenience make it easily compatible with existing optical microscope setups, making it a powerful tool for observing biological samples and detecting industrial defects.

Perspective on Dual‐Tower Concentrated Solar Power Plants

ABSTRACTThis paper presents a comprehensive analysis of dual‐tower concentrated solar power (CSP) plants, highlighting their key technical advantages, including improved efficiency and enhanced heat distribution. The novel dual‐tower design, implemented at Guazhou, Gansu Province by Three Gorges Renewables, significantly enhances optical efficiency and reduces spillage losses compared to traditional single‐tower systems. Utilizing molten salts or particle receivers, the dual‐tower configuration offers a more efficient thermal management approach. A comparative analysis of various designs underscores the trade‐offs between increased efficiency and capital costs. The paper also discusses the economic and environmental benefits, technical challenges, and future research directions associated with dual‐tower systems, providing valuable insights into their potential to advance solar thermal technology.

Comparative Techno-Economic Analysis of Parabolic Trough and Linear Fresnel Collectors with Evacuated and Non-Evacuated Receiver Tubes in Different Geographical Regions

In the context of Concentrated Solar Power (CSP) technology, this paper presents a comparison between the Parabolic Trough Collector (PTC) and the Linear Fresnel Collector (LFC), considering both evacuated and non-evacuated receiver tubes. The comparison was carried out in terms of the Levelized Cost of Electricity (LCOE) considering a reference year and four locations in the world, characterized by different levels of direct normal irradiation (DNI) from 2183 kWh/m2/year to 3409 kWh/m2/year. The LCOE depends on economic parameters and on the net energy generated by a plant on an annual basis. The latter was determined by a steady-state 1D model that solved the energy balance along the receiver axis. This model required computing the incident solar power and heat losses. While the solar power was calculated by an optical ray-tracing model, heat losses were computed by a lumped-parameter model developed along the radial direction of the tube. Since the LFC adopted a secondary concentrator, no conventional correlation was applicable for the convective heat transfer from the glass cover to the environment. Therefore, a 2D steady-state CFD model was also developed to investigate this phenomenon. The results showed that the PTC could generate a higher net annual energy compared to the LFC due to a better optical performance ensured by the parabolic solar collector. Nevertheless, the difference between the PTC and the LFC was lower in the non-evacuated tubes because of lower heat losses from the LFC receiver tube. The economic analysis revealed that the PTC with the evacuated tube also achieved the lowest LCOE, since the higher cost with respect to both the LFC system and the non-evacuated PTC was compensated by the higher net energy yield. However, the non-evacuated LFC demonstrated a slightly lower LCOE compared to the non-evacuated PTC since the lower capital cost of the non-evacuated LFC outweighed its lower net annual energy yield. Finally, a sensitivity analysis was conducted to assess the impact on the LCOE of the annual optical efficiency and of the economic parameters. This study introduces key technical parameters in LFC technology requiring improvement to achieve the level of productivity of the PTC from a techno-economic viewpoint, and consequently, to fill the gap between the two technologies.

Design rules for catalysis in single-particle plasmonic nanogap reactors with precisely aligned molecular monolayers

Plasmonic nanostructures can both drive and interrogate light-driven catalytic reactions. Sensitive detection of reaction pathways is achieved by confining optical fields near the active surface. However, effective control of the reaction kinetics remains a challenge to utilize nanostructure constructs as efficient chemical reactors. Here we present a nanoreactor construct exhibiting high catalytic and optical efficiencies, based on a nanoparticle-on-mirror (NPoM) platform. We observe and track pathways of the Pd-catalysed C-C coupling reaction of molecules within a set of nanogaps presenting different chemical surfaces. Atomic monolayer coatings of Pd on the different Au facets enable tuning of the reaction kinetics of surface-bound molecules. Systematic analysis shows the catalytic efficiency of NPoM-based nanoreactors greatly improves on platforms based on aggregated nanoparticles. More importantly, we show Pd monolayers on the nanoparticle or on the mirror play significantly different roles in the surface reaction kinetics. Our data provides clear evidence for catalytic dependencies on molecular configuration in well-defined nanostructures. Such nanoreactor constructs therefore yield clearer design rules for plasmonic catalysis.

Scalable fabrication approach and fill factor optimization for single pixel microlens arrays

Microlenses are a suitable approach to improve the performance of optical systems. An important optical efficiency determining parameter is the fill factor, which describes the relation of the lens area to the total optical active area. In this work, an optimization of the fill factor by optimizing the fabrication process steps is presented. The approach here is the use of i-line waferstepper lithography in combination with thermal reflow of photoresist and subsequent 1:1 pattern transfer in the lens material by reactive ion etching. For this method, the fill factor is determined by the minimum lens gap and, thus, the optical efficiency is strongly limited by the resolution limit of the i-line waferstepper lithography (350 nm). The goal of this investigation is to achieve the lowest possible lens gap even below the stepper-based resolution limit by optimizing each single process step without developing a new approach. The final result of the optimization was a fill factor improvement of 15%.

Ultra-compact dual-channel integrated CO2 infrared gas sensor

Expiratory CO2 concentrations can directly reflect human physiological conditions, and their detection is highly important in the treatment and rehabilitation of critically ill patients. Existing respiratory gas analyzers suffer from large sizes and high power consumption due to the limitations of the internal CO2 sensors, which prevent them from being wearable to track active people. The internal and external interference and sensitivity limitations must be overcome to realize wearable respiratory monitoring applications for CO2 sensors. In this work, an ultra-compact CO2 sensor was developed by integrating a microelectromechanical system emitter and thermopile detectors with an optical gas chamber; the power consumption of the light source and ambient temperature of the thermally sensitive devices were reduced by heat transfer control; the time to reach stabilization of the sensor was shortened; the humidity resistance of the sensor was improved by a dual-channel design; the light loss of the sensor was compensated by improving the optical coupling efficiency, which was combined with the amplitude trimming network to equivalently improve the sensitivity of the sensor. The minimum size of the developed sensor was 12 mm × 6 mm × 4 mm, and the reading error was <4% of the reading from −20 °C to 50 °C. The minimum power consumption of the sensor was ~33 mW, and the response time and recovery time were 10 s (@1 Hz), and the sensor had good humidity resistance, stability, and repeatability. These results indicate that the CO2 sensor developed using this strategy has great potential for wearable respiratory monitoring applications.

Processing wheat straw into a near-infrared light selective transmission film

This research focuses on the development of near-infrared light selective transmission film (NIR-LSTF) utilizing wheat straw biomass, extracting lignocellulose and lignin through the acetic acid method. Employing a hydrogel-based approach, lignin was encapsulated and underwent self-assembly both within and atop the hydrogel, enabling initial integration with cellulose. Hot pressing facilitated the thorough amalgamation of lignin into the cellulose matrix, enhancing the NIR-LSTF's resistance to environmental wear and creating a dense structure that minimizes light loss and reflection, thus outperforming traditional materials in optical efficiency and functionality. Moreover, the presence of lignin imparts the material with unique selective absorption characteristics, effectively blocking nearly all ultraviolet light and visible light (approximately 100 % at 610 nm and 78 % at 780 nm), while maintaining a high transmittance rate (∼90 %) in the near-infrared spectrum. This property underscores the films' significant potential in applications demanding near-infrared transparency. The efficacy of NIR-LSTF in the realms of infrared surveillance and privacy protection was assessed, yielding favorable experimental outcomes. This study paves a new pathway for the valorization of agricultural waste biomass within the near-infrared optical domain.

Output power analysis of low concentrated solar cells with fresnel lens optics

In this work, we introduce a П-shaped LCPV which works with a simple single-axis solar tracking system. The simulation of the П-shaped LCPV was made on COMSOL Multiphysics and output power of the LCPV was modeled and compared with other PV, LCPV systems using predicted optical efficiency at different incidence angles by regression methods such as XGBoost regression, Linear Regression, Support Vector Regression, Decision Tree Regression, Random Forest Regression. The most effective one was XGBoost regression with accuracy of 91.23931 %. The П-shaped LCPV generates 2.2 times more energy than the fixed nine-solar cell panel per a day. Using nine solar cells and the designed optics allows the system to operate well at wider incidence angles using a single-axis solar tracking system which rotates the system only 4 times a day. The П-shaped LCPV is less complex and cheaper than an ordinary Fresnel lens-based LCPV.

Frequency tuning of a squeezed vacuum state using interferometric enhanced acousto-optic effect

Quantum frequency conversion is one of the important tools for quantum information processing. So far, the frequency conversion of continuous variable quantum state in radio frequency range has not been demonstrated yet. Here, we experimentally demonstrate the optical frequency fine tuning of a squeezed vacuum state by using an acousto-optic modulator based bi-frequency interferometer. The systematic efficiency of the frequency tuning device is 91%, which is only confined by the optical transmission efficiency of the acousto-optic modulators. The amount of frequency tuning is 80 MHz, which is orders of magnitude larger than the line-width of the laser used to generate the squeezed state and can, in principle, be further extended. A squeezed vacuum state with −3.47 ± 0.02 dB squeezing level is sent to the frequency tuning device, and a squeezing level of −1.98 ± 0.02 dB is directly measured by a fiber coupled homodyne detector after the frequency tuning. Our scheme can also be applied to a variety of other quantum optical states as well and will serve as a handy tool for quantum networks.

A robust, fiber-coupled scanning probe magnetometer using electron spins at the tip of a diamond nanobeam

Abstract Fiber-coupled sensors are well suited for sensing and microscopy in hard-to-reach environments such as biological or cryogenic systems. We demonstrate fiber-based magnetic imaging based on nitrogen-vacancy (NV) sensor spins at the tip of a fiber-coupled diamond nanobeam. We incorporated angled ion implantation into the nanobeam fabrication process to realize a small ensemble of NV spins at the nanobeam tip. By gluing the nanobeam to a tapered fiber, we created a robust and transportable probe with optimized optical coupling efficiency. We demonstrate the imaging capability of the fiber-coupled nanobeam by measuring the magnetic field generated by a current-carrying wire. With its robust coupling and efficient readout at the fiber-coupled interface, our probe could allow new studies of (quantum) materials and biological samples.

Pushing Radiative Cooling Technology to Real Applications.

Radiative cooling is achieved by controlling surface optical behavior toward solar and thermal radiation, offering promising solutions for mitigating global warming, promoting energy saving, and enhancing environmental protection. Despite significant efforts to develop optical surfaces in various forms, five primary challenges remain for practical applications: enhancing optical efficiency, maintaining appearance, managing overcooling, improving durability, and enabling scalable manufacturing. However, a comprehensive review bridging these gaps is currently lacking. This work begins by introducing the optical fundamentals of radiative cooling and its potential applications. It then explores the challenges and discusses advanced solutions through structural design, material selection, and fabrication processes. It aims to provide guidance for future research and industrial development of radiative cooling technology.

Enhancing optical output power efficiency in nitride‐based green micro light‐emitting diodes by sidewall ion implantation

AbstractThough micro‐LED (light‐emitting diode) displays are considered the emerging display technology, the micron‐scale LED chip size encounters severe efficiency degradation that may impact the power budget of the displays. This work proposes an ion implantation method to deliberately create a high‐resistivity sidewall in the InGaN/GaN green LED. Our study demonstrates that ion implantation suppresses reverse leakage current due to the mitigation of sidewall defects. For an LED mesa size of 10 × 10 μm2, optical output power density is improved by 36.2% compared to the device without implantation. Compared to a larger 100 × 100 μm2 device without implantation, we achieve only 21.3% degradation of output power density under 10 A/cm2 injection for a 10 × 10 μm2 LED with implantation. In addition, the ion implantation method can lower the wavelength shift by reducing light emission from the region near the sidewall (where the amount of Indium [In] clustering differs from the mesa region). The results show promise in addressing the efficiency challenges of micro‐LED displays by selective ion implantation.

Bionically inspired flattened linear Fresnel concentrator and its photothermal application on building façade

The paper presents a low wind-load linear Fresnel concentrator (LFR) for solar energy harvesting on high-rise building façades. This concentrator, characterized by a significantly reduced thickness compared to conventional designs, is termed “flattened linear Fresnel concentrator.” The concentrator imitates the “Shade Avoidance Response” of plants by attaching a rod to the mirror to form an Off-axis mirror that mitigates inter-mirror blocking in a constrained space. The paper initially outlines a comprehensive overview of the bionic theory of the concentrator. Subsequently, the paper develops an optimization model and parameter calculation procedure for the two competing objectives of flattening profile and boosting optical efficiency. Based on this, the paper discusses in detail the advantages of flattened Off-axis concentrators for building facades. Finally, this paper conducted a photothermal comparison experiment with a conventional LFR device installed vertically, and by analyzing the experimental data, it was revealed that the photothermal efficiency of the Off-axis flattened concentrator was 10.82% higher than that of the conventional LFR device, and the photothermal efficiency in one day reached 57.43%. Additionally, the paper examines the sunlight self-adaptive feature of the flattened Off-axis concentrator, demonstrating its advantages for façade integration through experimental data analysis.

Fabrication and Performance Evaluation of a Directly Immersed Photovoltaic-Thermal Concentrator for Building Integration

A novel concentrating photovoltaic-thermal solar collector was designed, fabricated and experimentally investigated at the University of Lleida, in Spain. Two designs based on two dielectric liquids, isopropyl alcohol (IPA) and deionised water (DIW), were developed. In both cases, the solar cells were directly liquid-immersed. The study includes experiments and numerical simulations. The proposed concentrator was incorporated into a testing unit to examine its potential as a façade by controlling light and thermal flux transmitted into a building. The results show promising electrical performance and acceptable thermal performance, with thermal losses ranging from 14 to 20 W °C−1m−2. The optical efficiency was around 73% in the case of the concentrator with DIW and about 76% for the one with IPA. Regarding electrical performance, the fill factors for IPA and DIW configurations are as follows: 62.8% and 61.7%, respectively. The comparison results reveal striking differences between the testing unit with and without solar concentrators, with the concentrator-equipped unit showing around four times lower illuminance and a 50% reduction in maximum heat fluxes and interior temperature. Generally speaking, it can be said that these energy-generating façades show satisfactory behaviour and offer interesting possibilities for building-integrated applications.