Advanced Photonics Research最新文献

Intelligent characterization of van der Waals semiconductors is an essential process for industrial manufacturing and laboratory fabrication. A combination of microscopic images and artificial intelligence models is an efficient way for wafer-scale layer number identification of van der Waals semiconductors. This methodology overcomes the bottleneck of the conventional manual layer number counting approach, which requires a long period of manual inspection and induces high error rates when distinguishing layers with similar appearance. Here, a convolutional architecture that involves a fused network of ResNet-Inception with Attention Layer (RIAL) is developed for accurate multiclass classification of randomly distributed layers of chemical vapor deposition (CVD)-grown van der Waals semiconductors. RIAL model is first validated on the single-label datasets CIFAR-10/100, and subsequently fine-tuned on the custom-built microscopic image datasets of CVD-grown MoS₂. To compare with semantic segmentation, U-Net with Attention Layer (UNAL) is further implemented for pixel-wise classification of multiclass semiconductors. The quantitative analysis of RIAL and UNAL illustrates the versatility of attention convolutional network models in the wafer-scale identification of van der Waals semiconductors.

Highly demanding modern IR nanophotonic devices with spectrally sharp resonances often require precise fabrication methods or precisely controllable material responses to ensure appropriate spectral performance. In this context, photonic architectures based on low-loss thermo-optical materials have recently shown the possibility of yielding narrowband-resonance spectra and present accurate spectral adjustability in the order of a few tens of nanometers. Another way to adopt the temperature-driven optical effect of Si is demonstrated by achieving wide-band and highly precise spectral adjustability of the IR resonance wavelength in multilayered ultranarrowband photonic devices based on Si/SiO₂ distributed Bragg reflectors. This new approach is based on controlling the continuous and irreversible amorphous-to-crystal transformation of Si, yielding a colossal shift in the refractive index of Si, which results in wide-band spectral adjustability of the resonance wavelength of the fabricated devices by up to 100 nm. This design strategy can be adopted for other high-refractive-index materials such as Ge to achieve spectrally selective photonic devices with ultrafine wavelength tunability operating in the IR to near-infrared regions, such as narrowband thermal emitters and spectroscopic sensors.

Second-Harmonic Generation

In their Research Article (10.1002/adpr.202500033), Kung-Hsuan Lin and co-workers show that few-layer SnSe with ferroelectric stacking exhibits second harmonic generation (SHG) efficiencies up to three orders of magnitude higher than conventional nonlinear crystals. The SHG response is highly anisotropic and strongly dependent on the excitation wavelength.

Optical Antennas

A nanosphere(Cu₂O)-film(Au) hybrid resonator traps a visible photon and funnels the energy to creation of an electron-hole pair in gold. The resonant enhancements enable monitoring of interband transitions in Au for single Cu₂O particles. The reverse process, fluorescence from gold, is also observed for single particles with giant Purcell factors. More information can be found in the Research Article by Ali Kaan Kalkan and co-workers (10.1002/adpr.202400126).

Fourier ptychography microscope (FPM) is a computational imaging technique that can achieve a large field-of-view and high-resolution retrieval of complex-amplitude object function from a set of low-resolution intensity images. This study investigates the effects of system-model discrepancies in FP reconstruction under diverse scenarios characterized by experimental errors, including axial mispositioning of specimens, sample thickness, and factors affecting k-vector sampling positions—magnification, light-emitting diode (LED) height, and positional errors of LED elements. With the systematic investigation using experimental data and Gauss-Newton algorithm, we provided the level of tolerance for different types of experimental errors and its general relation to configurational parameters for FPM, such as the numerical aperture of objective lens, synthetic numerical aperture, and the spectrum overlapping ratio of low-resolution images. Also, we found that different types of errors can generate characteristic effects on the appearance of the reconstructed images, and therefore, reconstruction results could be highly inconsistent under various conditions of system-model mismatch, even if the reconstructed images are seemingly plausible. The investigation highlights the need for an improved algorithmic approach to physically accurate retrieval of complex-amplitude maps using a FPM.

The AlGaN/GaN quantum-well heterostructures typically exhibit a positive photoconductivity (PPC) during the light illumination. Surprisingly, the introducing the GaN/AlN superlattice (SL) back barrier into N-polar AlGaN/GaN quantum-well heterostructures induces a transition in these heterostructures from PPC to negative photoconductivity (NPC) as the SL period number increases at room temperature. This transition occurs under an infrared light illumination and can be well explained in terms of the excitation of hot electrons from the 2D electron gas and subsequent trapping them in a SL structure. The NPC effect observed in N-polar AlGaN/GaN heterostructures with SL back barrier exhibits photoconductivity yield exceeding 85$�\%$ and thus is the largest ones reported so far for semiconductors. In addition, the NPC signal remains relatively stable at high temperatures up to 400 K. The obtained results can be interesting for the development of NPC related devices such as photoelectric logic gates, photoelectronic memory, and infrared photodetectors.

The all-inorganic lead halide perovskites, including cesium lead iodide (CsPbI₃), have attracted significant attention due to their possible applications in photovoltaics, light-emitting devices, and other optoelectronic technologies, driven by their intrinsic optoelectronic properties. This study introduces a simple, green, and scalable solution synthesis method for the CsPbI₃ perovskite fabrication, utilizing β-diketonate [Cs(hfa)]_n and [Pb(hfa)₂diglyme]₂ precursors and ethanol as solvent. The as-synthesized nanoribbons are initially fabricated in the pure yellow δ-phase, as confirmed by X-ray diffraction and energy-dispersive X-ray analysis. Thermal analysis through differential scanning calorimetry highlights the reversible phase transition from δ-CsPbI₃ to the black cubic α-phase. The photoactive and metastable black γ-CsPbI₃ is obtained via high-temperature annealing and rapid cooling under inert conditions. Optical characterizations have been performed in order to extrapolate a bandgap of 2.89 eV for the δ-phase and 1.62 eV for the γ-phase, while the photoluminescence analysis displays intense emissions at 530 and 700 nm for the δ- and γ-phase, respectively. Ambient photoemission spectroscopy further elucidates the energy levels of the γ-phase, determining a highest occupied molecular orbital energy of 5.68 eV and a work function of 4.32 eV. These findings demonstrate the possibility to synthesize pure CsPbI₃ and obtain the γ-CsPbI₃ phase with promising applications.

Electroceuticals are a novel type of therapeutics that employ electrical stimulation to modulate neural circuits and recover impaired physiological functions. Traditional systems using implanted leads as electrode and/or connecting wires pose several clinical challenges, including infection risk, anatomical incompatibilities, and leads dislodgement. Recent progress in optoelectronic biointerfaces is establishing new paradigms for electroceutical intervention by enabling precise, minimally invasive, and nongenetic neuromodulation through light-driven wireless technologies. In this review, first, the modulation mechanism of representative organic and inorganic semiconductor-based optoelectronic biointerfaces is demonstrated, which can be designed into flexible and tissue-conforming architectures. Then, further their capabilities to modulate structures at various levels, including neurons, nerve tissues, and the cerebral cortex are emphasized. Beyond neuromodulation, their promising therapeutic value and translational potential are highlighted, encompassing vision restoration, nerve regeneration, and treatment of Parkinson's disease. Together, these advancements mark a transformative shift toward next-generation bioelectronic medicine.

A theoretical and experimental characterization of the optical modes of dispersionless ring cavities incorporating phase modulators (PM) and/or frequency shifters (FS) is presented. Using linear operator theory, the exact response of these cavities to arbitrary modulating waveforms and optical inputs is computed and shown to be a filtering process that selects a certain class of fields, invariant under multiple roundtrips, which are identified with the cavity's optical modes. The different types of PM/FS cavity modes are analyzed. This approach also leads to a representation of these cavities as unmodulated resonators preceded and followed by complementary phase modulations, which are linearly related to the imparted intracavity phase modulation or frequency shift. The theory is experimentally validated by the external injection of engineered phase and frequency modulated cavity modes in an Er:fiber PM fiber loop, and also compared with the emission modes of frequency modulated lasers and continuous wave (CW) frequency shifted feedback lasers. These results provide a unified view for the linear analysis of systems employing PM/FS active cavities or resonators, of interest in the field of photonic signal generation and processing.

Ultrafast events, from the rapid propagation of shock waves to molecular vibrations and electron dynamics, can unfold on timescales as short as femtoseconds. Limited by the imaging speed of charge-coupled device and complementary metal-oxide-semiconductor sensors, conventional imaging systems cannot capture such high-speed phenomena. Researchers have developed various ultrafast photography techniques to address this challenge, incorporating electronic, mechanical, and optical methods to achieve imaging speed in the trillion frames per second. This review categorizes ultrafast photography into four types: multishot passive technique, multishot active technique, single-shot passive technique, and single-shot active technique. It examines the evolution from early mechanical and electronic high-speed cameras to modern optical and computational imaging. These innovations have broad applications in physics, chemistry, biology, and engineering, providing new insights into ultrafast dynamics. This review discusses the latest developments, compares key techniques, and explores future directions in ultrafast photography research.