Advanced Photonics Research最新文献

Organic photodiodes (OPDs) have made remarkable strides and now poised to surpass traditional silicon photodiodes (PDs) in various aspects including linear dynamic range (LDR), detectivity, wavelength selectivity, and versatility.^[1] Tunable mechanical and optoelectronic properties of organic semiconductors, coupled with lower process costs, have propelled OPDs into the spotlight across fields such as wearable light fidelity systems, flexible image sensors, and biomedical imaging.^[2–5] While most advanced organic imaging systems to date rely on polymer-based solution processes, challenges such as the use of toxic organic solvents and reproducibility issues hinder their commercialization.^[6,7] Vacuum-processed OPDs offer a promising alternative, boasting eco-friendliness and compatibility with large-scale fabrication facilities.^[8,9] In this review, recent advancements and challenges in vacuum-processed OPDs, an area that has received less attention compared to solution-processed counterparts, are explored. Herein, four primary pathways for development of vacuum-processed OPDs are outlined: 1) ultraviolet-selective OPDs, 2) visible-light-selective OPDs, 3) near-infrared or short-wave-infrared-sensitive OPDs, and 4) addressing challenges such as higher noise currents compared to inorganic PDs. In this review, it is aimed to furnish readers with a comprehensive understanding of vacuum-processed OPDs, spanning from materials design to device engineering.

Carbon dots (CDs) show great application potential with their unique and excellent performances. Coal and its derivatives are rich in aromatic ring structure, which is suitable for preparing CDs in microstructure. Coal-burning dust from coal-fired power plants can be utilized as a rich resource to separate and extract CDs. It is shown in the results that there are two main possible mechanisms for the formation of CDs in coal-burning dust. One is the self-assembly of polycyclic aromatic hydrocarbons contained in coal or produced by incomplete combustion of coal. The other mechanism is that the bridge bonds linking different aromatic structures in coal break, which will form CDs with different functional groups when the coals burn at high temperature. Under violet light excitation at 310–340 nm or red light at 610–640 nm, CDs extracted from coal-burning dust can emit purple fluorescence around 410 nm. The mechanism of up-conversion fluorescence emission of CDs is due to a two-photon absorption process. The recycling of CDs from coal-burning dust from coal-fired power plants are not only good to protect environment but will also be helpful for mass production of CDs.

Herein, deep learning-ghost imaging (DLGI) based on a digital micromirror device is realized to avoid the difficulties of a charge-coupled device (CCD) scientific camera being unable to obtain the sample images in extremely weak illumination conditions and to solve the problem of the inverse relationship between imaging quality and imaging time in practical applications. Deep learning for computational ghost imaging typically requires the collection of a large set of labeled experimental data to train a neural network. Herein, we demonstrate that a practically usable neural network can be prepared based on the simulation results. The acquisition results of the CCD scientific camera and the simulation results with low sampling are used as the training set (1000 observations) and we can complete the data acquisition process within one hour. The results show that the proposed DLGI method can be used to significantly improve the quality of the reconstructed images when the sampling rate is 60%. This method also reduces the imaging time and the memory usage, while simultaneously improving the imaging quality. The imaging results of the proposed DLGI method have great significance for application in clinical diagnosis.

With increasing demand for energy saving and environmental sustainability, electrochromic devices (ECDs) are considered as emerging display devices with low energy consumption. While various reflective-type displays produce images with low energy, achieving full color displays often involves much device complexity and nonflexibility. Multicolor ECDs aim to realize full color reflective-type displays, surpassing the current monochromic type or limited coloration capabilities in a 1D color space. Enhancing device flexibility is also highly desirable for use of ECDs in wearable and flexible electronics for health monitoring and advanced textiles with easy visualization. In this review, recent advances in multicolor and flexible ECDs are examined. Several primary strategies to achieve multicolor ECD are described, including material modifications, color overlay, and dye-mediated colorations. In addition, recent developments in flexible ECDs are explored, emphasizing novel materials and fabrication processes that improve mechanical durability and reliability under deformation. It is expected that this review will provide a comprehensive understanding of multicolor and flexible ECDs for applications in smart windows, displays, and wearable electronics.

The remarkable properties of toroidal metasurfaces, featuring ultrahigh-Q bound states in the continuum (BIC) resonances and nonradiating anapole modes, have garnered significant attention. The active manipulation of quasi-BIC resonance characteristics offers substantial potential for advancing tunable metasurfaces. This study explores explicitly the application of vanadium dioxide, a phase change material widely used in active photonics and room-temperature bolometric detectors, to control quasi-BIC resonances in toroidal metasurfaces. The phase change transition of vanadium dioxide occurs in a narrow temperature range, providing a large variation in material resistivity. Through heating thin film patches of vanadium dioxide integrated into a metasurface comprising gold split-ring resonators on a sapphire substrate, remarkable control over the amplitude and frequency of quasi-BIC resonances is achieved due to their high sensitivity to losses present in the system. Breaking the symmetry of meta-atoms reveals enhanced tunability. The predicted maximum change in the quasi-BIC resonance amplitude reaches 14 dB with a temperature variation of ≈10 °C.

Topological Photonic Insulators

In article number 2400023, Vien Van and Hanfa Song present the design and realization of (2 + 1)D topological photonic insulators hosting all flat bands, which exhibit novel properties such as anomalous Floquet insulator phase, ultra-wide edge mode continuum, super robustness to disorder, and photon caging in compact localized bulk states. These lattices have broadband applications in topologically-protected quantum photonics and programmable photonic circuits.

The hole accelerator is proven to benefit the hole injection for traditional light-emitting diodes (LEDs) because the induced electric field provides the holes with more kinetic energy to pass through the electron-blocking layer, enhancing the hole injection efficiency. Herein, the effect of the hole accelerator (HA) layer on the micro-LEDs by modeling the characteristics of the devices with a current density of lower than 10 A cm⁻² is investigated. The simulation results show that the appended HA layer brings a knot of the electric field in the HA layer, leading to higher internal quantum efficiency (IQE) than the device without HA under the low current density. The thickness and composition of HA, the quantum number, and the material of quantum barrier are also simulated and analyzed. The simulated radiative, Shockley–Read–Hall, and Auger recombination rates show that the IQE of the micro-LED with the HA layer is higher than that without the HA layer under the current density of lower than 10 A cm⁻².

Photoinduced Structural Modification

In article number 2300326, Ashim Dhakal and co-workers show that photo-induced metastable modification of electronic structure in graphite allows for multiphoton processes that can up-convert an O-band infrared excitation to visible-NIR band in graphite powder. Theoretically, this process can upconvert an infrared light near the wavelength of 3 μm to VIS-NIR wavelengths. It opens exciting new avenues for applications in visible light generation and low-noise imaging using infrared light excitation.

Herein, a novel approach is presented to mitigate the fluorescence interference during the detection of vibrational signal via the stimulated emission depletion (STED). STED is the mechanism commonly employed in optical imaging; however, its application should not be confined solely to this field. To explore additional possibilities, a novel application of STED in vibrational spectroscopy detection is introduced. Vibrational spectroscopy is a widely used technique for the material detection and identification, but its sensitivity is influenced by impurity signals, especially the fluorescence. The proposed method is capable of suppressing fluorescence without influencing vibrational signal. At the low concentration of fluorescent impurities, the signal-to-background ratio of vibrational spectroscopy is 2.6 times as high as that without this method. The introduction of depletion light can enhance the detection of vibrational signals, resulting in more optimal signal detection. A promising new application of STED other than super-resolution imaging is investigated.

Optically pumped threshold fluences are a widely reported metric to benchmark the performance of thin-film gain media and lasers. Estimating the threshold fluence for nonhomogeneous beams, such as a circular Gaussian excitation, is not trivial since the average fluence depends on the estimated spot diameter. Using an exemplary lead halide perovskite film, the inversion volume at different pump energies is mapped. It is shown that the peak fluence of an arbitrary spatial beam profile is more relevant at the threshold, as it provides an upper bound to the threshold fluence. Also, simple conversion factors to estimate the peak fluence using Gaussian excitation beams are provided and the methodology to arbitrary profiles is extrapolated. Furthermore, it is advocated for using flat-top or uniform stripe excitations to unambiguously extract the threshold fluence, since these excitations display minor discrepancies between the average and peak fluence, and keep the inversion volume relatively constant during the measurement.