Advanced Photonics Research最新文献

With the rapid development of communication networks and computing, optical switches as an important elementary unit are highly needed. In this article, a silicon-based optical switch with $��{�\text{Ge}�}_2�{�\text{Sb}�}_2�{�\text{Te}�}_5�$ (GST)-enabled phase-shifting region is proposed. This optical switch is based on contra-directional couplers composed of two phase-shifted Bragg gratings. To minimize the impact of GST absorption loss, GST is only used in the phase-shifting area, and the switching function is achieved by changing the state of GST. In the results, it is shown that the proposed device has a 3 dB operation bandwidth of about 163.2 GHz (1.394 nm) and an extinction ratio of about 19.06 dB for the drop port and about 20.25 dB for the through port. The loss at the central operational wavelength is about 1.3 and 1.04 dB for the through port and the drop port, respectively, and the largest loss over the entire operation bandwidth for these two ports is 1.66 and 2.35 dB. Furthermore, the optical switch is shown to be bidirectional, achieving similar performance when light propagates in the opposite direction. Compared with previous works, the proposed optical switch realizes wider operation bandwidth, higher extinction ratio, and lower loss.

This article develops a Monte Carlo model to optimize a newly introduced tandem luminescent solar concentrator. This innovative structure comprises two parallel transparent polymeric waveguides separated by an air gap. The first waveguide, which is exposed to sunlight, contains fluorophores and performs as a traditional luminescent solar concentrator. In contrast, the second waveguide is equipped with an inner polarization volume grating layer, strategically placed to couple the emitted photons within the escape cone, directing them into the second waveguide and preventing reabsorption. The finite difference time domain method is employed to optimize the performance of this grating. The results show a significant improvement in external photon efficiency compared to the conventional luminescent solar concentrator.

Herein, a holographic optical element (HOE) printing technique which maintains shapes and sizes of hogels across diverse focal positions, and aberration-corrected HOEs which are fabricated by it are proposed. The proposed HOE printer employs nonpixelated focus modulators composed of double 4f optics in reference and signal beam paths to record hogels with the consistent shapes, which is validated via the ray tracing simulation. An optimization algorithm is developed for aberration-corrected HOEs, dedicated to the proposed printing system. Imaging simulations verify the improved image quality compared to a baseline case by showing a 5 times sharper point spread function. As the experimental verification, a HOE printer is realized, which provides 1 × 1 mm of hogels consistently over 20° × 20° of angular ranges and 8 diopters of focal length changes. Displaying experiments using printed HOEs (mono-colored and full-colored ones) verify the proposed method with aberration-corrected and see-through images.

GaN-Based Blue Laser Diodes

In article number 2400119, Wenyu Kang, Junyong Kang, and co-workers develop an anti-aging technology for high-power GaN LD from mechanism investigation to degradation suppression. This cover depicts a person in different aging stages, indicating the severe degradation issues in high-power LD and the effectiveness of this anti-aging technology.

Spintronic Terahertz Emitters

In article number 2400064, Mathias Vanwolleghem and co-workers experimentally demonstrate a close to 100-fold improvement of the power efficiency of inverse spin Hall emitters by maximizing the impact of the electromagnetic environment of the nanometric emitter. As a result, by moving from a basic emitter on a bare substrate to one functionalized by a resonant crystal cavity and an impedance matched emitting substrate, the emitted THz field pulses can reach several MV/cm peak strengths without any echo behavior.

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.

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.