Advanced Photonics Research最新文献

Optical Convolutional Neural Networks

In article number 2400108, Weiwei Tan, Jiale He, Guanhai Li, Xiaoshuang Chen, and co-workers propose an optical neural network that leverages GST-based microring waveguides for on-chip computing, offering 64 levels of transmission contrast with 6-bit resolution. It achieves high accuracy in image edge detection and recognition with potential for large-scale photonic neural networks.

Metalens THz Emitter

In article number 2400125, Hyunseung Jung, Oleg Mitrofanov, and co-workers present a metalens for achieving focused terahertz (THz) beam generation using InAs nanoscale resonators. This metalens enables binary-phase THz pulse generation under ultrafast near-IR pump excitation, paving the way for a flexible and compact THz generation platform for applications in imaging, spectroscopy and communications.

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.

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.

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 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.

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.

2D Layered Superconductors

In article number 2400045, Kaveh Delfanazari showcases methods for the realization of ultrafast terahertz (THz) metamaterial photonic switches on a few nanometer-thick layered high-temperature superconductor van der Waals (vdWs). The metamaterial array offers active modulation of THz amplitude and phase with an ultrafast-picosecond-switching timescale. The device holds promise for the development of future THz communication circuits and systems operating at cryogenic temperatures.