Advanced Photonics Research最新文献

Graphene-based absorbers have various modern applications across industries due to their exceptional properties. Some common applications include: thermal management and energy storage. Herein, the design and simulation of a broadband tunable absorber based on graphene with perfect absorption spectra in the near-infrared region are reported. The proposed structure consists of an MgF₂ layer and golden disc surrounded by L-shaped golden arms placed on single layer of graphene. The structure guarantees polarization-insensitive (PI) performance under normal incident due to the symmetrical design. The investigation of the PI of the structure reveals almost similar absorption for oblique incident angles up to 55° for TM and up to 60° for TE polarization. The desirable resonance wavelength is achievable by tuning the geometrical parameters. By changing the chemical potential of graphene, the absorption and bandwidth of absorber are controllable. A full width at half maximum of 330 nm is another superiority of this absorber. These considerable aspects of the proposed structure make it practical for varieties of applications such as cloaking, sensing, switching, and so on.

In this work, a comparative analysis of gallium nitride (GaN) thin films is conducted, both with and without photonic crystal (PhC) structures, focusing on their scintillation and photoluminescence properties. GaN's suitability for diverse optoelectronic and radiation detection applications is analyzed, and this study examines how PhC implementation can enhance these properties. Methodologically, the emission spectra is analyzed from 5.9 keV X-ray sources, decay curves, pulse height spectra in response to ²⁴¹Am 5.5 MeV alpha-rays, and photoluminescence spectra induced by UV excitation. The findings demonstrate a substantial increase in quantum efficiency for PhC GaN, nearly tripling the light yield that of conventional plain GaN thin films under the UV excitation. The enhancement is predominantly attributed to the PhC GaN's proficiency in guiding light at 550 nm, a feature indicative of its spectral filtering capabilities, as detailed in the study. Furthermore, side-band scintillations, stemming from inherent materials like Chromium that generate scintillations at diverse wavelengths, are effectively mitigated. A key finding of this study is the effective detection of light not only at the rear but also along the lateral sides of the films, offering new possibilities for radiation detector design and architecture.

The search for alternatives to Pb-based perovskites, due to concerns about stability and toxicity, has led to the exploration of Pb-free options. Tin (Sn) and bismuth (Bi) are promising candidates, given their similar ionic radii to Pb and the isoelectronic nature of Pb²⁺ and Bi³⁺, which suggest comparable chemical properties. Among these, CsSnBr₃ and Cs₃Bi₂Br₉ are relatively underexplored but offer lower toxicity and enhanced stability while demonstrating optoelectronic properties suitable for various applications. In this study, CsSnBr₃ and Cs₃Bi₂Br₉ nanocrystals are synthesized using a colloidal method and integrated into Schottky diodes. X-ray photoelectron spectroscopy analysis of the surface chemistry confirms improved thermal and phase stability compared to Pb-based perovskites. Schottky diode parameters, including ideality factor, barrier height, and series resistance are assessed using conventional thermionic emission, modified Cheung's, and Norde's models. The Cs₃Bi₂Br₉-based Schottky diode exhibits superior electrical performance with the lowest series resistance and optimal barrier height. Electrical impedance spectroscopy results indicated that CsSnBr₃ has higher resistances and lower capacitances than Cs₃Bi₂Br₉, reflecting lower charge carrier mobility and more defects, although the R₁C₁ regions in both materials demonstrated faster charge dynamics, making them ideal for high-speed applications.

In nature, dynamic camouflage is performed by cephalopods and reptiles. Humans attempt to perform dynamic camouflage by employing display devices to show the surrounding background. In this work, a switchable camouflage device based on an electrophoretic display (EPD) is proposed. Color-filter EPDs display colors by reflecting light through the color filters and black-and-white EPDs. The number of subpixels is found to be an important factor on color performance. To improve the poor saturation of color-filter EPDs, the number of color filter subpixels is reduced. Compared with filters with three and four subpixels, a dual-subpixel filter proposed in this work significantly improves the average saturation of red, green, and blue colors, with increases of 49% and 112%, respectively. Subsequently, the spectral characteristics of the color filter and black-and-white EPD are optimized by using genetic algorithm to reduce the average color difference between the display and the switchable target color, which can be reduced as low as 0.18. To visually demonstrate the color reproduction capability of the dual-subpixel EPD, sample applications including the switchable vegetation and digital camouflages are designed and have a high degree of agreement with the background. In this work, an innovative and effective approach is introduced to dynamic camouflage.

High-frequency broadband ultrasound in nested antiresonant hollow core fibers (NANFs) is investigated for the first time. NANFs have remarkable features enabling high-resolution microscale optoacoustic imaging sensors and neurostimulators. Solid optical fibers have been successfully employed to measure and generate ultrasonic signals, however, they face issues concerning attenuation, limited frequency range, bandwidth, and spatial resolution. Herein, highly efficient ultrasonic propagation in NANFs from 10 to 100 MHz is numerically demonstrated. The induced pressures and sensing responsivity are evaluated in detail, and important parameters for the development of ultrasonic devices are reviewed. High pressures (up to 234 MPa) and sensing responsivities (up to −207 dB) are tuned over 90 MHz range by changing the diameters of two distinct NANF geometries. To the best of knowledge, this is the widest bandwidth reported using similar diameter fibers. The results are a significant advance for fiber-based ultrasonic sensors and transmitters, contributing to improve their efficiency and microscale spatial resolution for the detection, diagnosis, and treatment of diseases in biomedical applications.

The AlGaN materials system has been extensively studied in order to improve the efficiency of UV-B and UV-C light-emitting diodes (LEDs). While progress has been made, significant challenges remain at shorter wavelengths. Most notably, increased Al composition for shorter-wavelength operation results in increased activation energy of Mg dopants, resulting in low p-doping. Although p-doped h-BN, with a bandgap of 5.9 eV, has been proposed as a potential replacement of p-doped AlGaN, there have not been demonstrations of LEDs fabricated from p-doped h-BN/AlGaN heterostructures. Such unique heterostructures combine 2D p-doped h-BN materials with 3D AlGaN materials. Herein, fabrication and characterization of p-doped h-BN/AlGaN multiple quantum wells (MQWs)/n-AlGaN LEDs, demonstrating emission of light at 290 nm corresponding to the AlGaN MQWs, with weaker emission at 262 nm corresponding to the AlGaN barrier, are reported. These results conclusively show hole injection through p-doped h-BN into AlGaN and provide a proof of concept that p-doped h-BN can be an alternative hole injection layer for UV LEDs.

In the More-than-Moore era, the explosive growth of data and information has driven the exploration of alternative non-von Neumann computational paradigms. Photonic neuromorphic computing has emerged as a promising approach, offering high speed, wide bandwidth, and massive parallelism. Herein, a high-resolution optical convolutional neural network (OCNN) is introduced using phase-change material Ge₂Sb₂Te₅ (GST)-based microring hybrid waveguides. This on-chip optical computing platform integrates GST into photonic devices, enabling versatile programming and in-memory computing capabilities. Central to this platform is a photonic convolutional computational kernel, constructed from photonic switching cells embedded with GST on a microring resonator. This programmable photonic switch leverages the refractive index modulation during the GST phase transition to achieve up to 64 discrete levels of transmission contrast, suitable for representing matrix elements in neural network algorithms with 6-bit resolution. Using these matrix elements, an OCNN capable of performing parallelized image edge detection and digital recognition tasks with high accuracy is demonstrated. The architecture is scalable for large-scale photonic neural networks, offering ultrahigh computational throughput, a compact design, complementary metal-oxide-semiconductor-compatible fabrication, and broad bandwidth.

Supercontinuum (SC) sources covering near-infrared and midinfrared region have attracted enormous interest and found significant applications in tissue imaging, sensing, spectroscopy, defense, and environmental monitoring. Herein, an 8.45 W all-fiber ultraflat SC source with a spectral range of 1.01–4.05 μm using a flat high-power 1.9–2.7 μm SC fiber source to pump a piece of fluorotellurite fiber is presented. The SC spectrum exhibits a 3 dB bandwidth of 1850 nm, ranging from 1870 to 3720 nm, and a 10 dB bandwidth of 2770 nm, ranging from 1120 to 3890 nm. The measured power stability is 0.19% (root mean square) for 5 h of continuous operation, proving the excellent power stability of the system. To the best of knowledge, the SC spectrum exhibits the widest reported 3 and 10 dB bandwidths for 1–4 μm SC sources.

Recording and manipulating optical waves with functional structures are crucially important for many applications. Herein, the submicron pillar arrays of an azo molecular glass (IA-Chol) are explored to show functional synergy of a recording medium and a diffractive optical element. The image recording is achieved through the pillar deformation along the electric-field oscillation direction of incident light. When illuminated with a polarized beam, the reconstructed images appear in the first-order diffraction spots of the pillar array with the tailored intensity distributions depending on the states of polarization of the recording beam and the image reconstruction beam. This approach enables several images to be recorded in the adjacent zones of the same pillar array using lights with different polarization directions, and then the images are reconstructed separately or simultaneously upon the polarization directions of the illumination light. Furthermore, the topographic features of the pillar array after the recording are replicated by replica-molding to the surfaces of polydimethylsiloxane (PDMS) slices as negative replicas and transformed to surfaces of poly(methylmethacrylate) (PMMA) films through hot-embossing. The PDMS and PMMA replicas are highly transparent in the visible light range and able to produce the reconstructed images with light in a wide-wavelength extent.

Metasurfaces have opened doors to combining multiple photonic functionalities in a single compact device. In particular, the ability to generate short terahertz (THz) pulses with precise wavefront engineering in a single THz metasurface redefined the role metasurfaces can play in THz systems. Here, an InAs metalens emitter which generates and focuses a THz pulse beam is demonstrated using a 130 nm thick InAs metasurface designed as a binary-phase Fresnel zone plate. The THz beam is focused to a spot of ≈430 μm at 1 THz with a short focal length of 5 mm and large numerical aperture of 0.5. Nanoscale InAs Mie resonators comprising the metasurface enable THz generation with an amplitude as high as 20 times compared to plasmonic THz emitters and several times compared to a 1 mm thick ZnTe crystal. This InAs metasurface emitter provides a new paradigm for designing THz imaging, spectroscopy, and communication systems, where THz beam generation and shaping are performed with a single device without compromising the generation efficiency, while eliminating losses and avoiding limitations of phase matching of conventional nonlinear optics approaches.