Compact, electrically driven terahertz (THz) sources remain a major bottleneck for chip-scale spectroscopy, imaging and high-speed wireless links. AlGaN/GaN two-dimensional electron gas (2DEG) systems have been investigated for THz emission, but experimental demonstrations have almost exclusively used Ga-polar platforms. Here we report a room-temperature THz signal from N-polar GaN grating-gate high-electron-mobility transistors (HEMTs) under pulsed electrical excitation. In the reversed-polarization heterostructure, the GaN channel lies above the AlGaN barrier, a geometry that places the channel close to the surface grating. The detected THz power increases with lateral electric field and square-wave duty cycle, whereas the apparent conversion efficiency falls at high duty cycle, consistent with increased Joule heating. Spectral measurements reveal a broad low-frequency feature and a gated/ungated spectral difference. The long-pulse room-temperature response is consistent with predominantly thermal emission, and the gated/ungated difference may reflect geometry-dependent thermal emissivity. These measurements do not establish a separate collective 2DEG contribution or a plasmonic resonance. These results establish an experimental N-polar GaN HEMT platform for studying electrically driven THz radiation and motivate calibrated emissivity, polarization-resolved and gate-tunable measurements.
Two-dimensional (2D) and quasi-2D lead-free halide double perovskites (LFHDPs) have gained significant attention as promising alternatives to conventional lead-based perovskites due to their superior environmental stability, reduced toxicity and versatile structural chemistry. This review provides a comprehensive overview of recent advances in the structural design, scalable synthesis strategies, and optoelectronic functionalities, with particular emphasis on bandgap tunability, strong excitonic effects, and photoluminescence quantum yields of 2D LFHDPs. We examine emerging trends in dimensional engineering, particularly the development of Ruddlesden–Popper and Dion–Jacobson phases incorporating monovalent and trivalent cations, which enable enhanced moisture resistance and tailored quantum confinement. Key challenges remain, including indirect bandgaps, limited carrier mobilities, defect-related trap states, and difficulties in large-area processing. To address these issues, innovative approaches such as compositional alloying, halide mixing, defect passivation, and hybrid device architectures are discussed. Furthermore, we discuss challenges such as limited light absorption, poor carrier mobility, and defect tolerance, and explore innovative strategies to overcome these restrictions. Finally, we outline future research directions that couple computational screening with experimental synthesis, integrate LFHDPs into flexible and neuromorphic devices, and pursue sustainable, low-cost compositions, emphasizing their potential in sustainable optoelectronic technologies.
2 μm fiber lasers, owing to their unique physical and spectral properties, hold significant potential for applications in fields such as lidar, medical surgery, environmental monitoring, and nonlinear frequency conversion. This paper presents a comprehensive review of continuous-wave and pulsed 2 μm fiber lasers. First, it elucidates the spectral characteristics and energy-level transition mechanisms of the primary gain media, including thulium-doped, holmium-doped, and thulium-holmium co-doped fibers. It systematically summarizes technical approaches, efficiency optimization strategies, and specialized fiber structures for high-power operation using mainstream pumping schemes such as 790 nm, 1.55 μm, and 1.9 μm pumping. Second, it discusses key technological methods and recent research progress for two typical operational modes: continuous-wave (multi-longitudinal mode, narrow linewidth) and pulsed (Q-switched, mode-locked, gain-switched). Finally, the primary bottlenecks limiting the high-power output and beam quality optimization of 2 μm fiber lasers are analyzed. Future development directions are proposed from five perspectives: system integration and miniaturization, ultra-wide spectral tuning, artificial intelligence-based control, advancements in high-power technology, and the development of novel gain materials.
Optoelectronic synapses that integrate sensing and synaptic weight modulation are key enablers for brain-inspired computing. Here, we report an Mg0.1Zn0.9O/TiO2 (MZO/TiO2)-based optoelectronic synaptic device capable of emulating essential biological synaptic functions, including paired-pulse facilitation, short- and long-term plasticity, as well as potentiation and depression. While electrical stimulation alone leads to volatile synaptic responses, the introduction of 365-nm optical excitation enables nonvolatile behavior, allowing more effective emulation of learning and memory. The device further supports basic arithmetic operations and, when integrated into a LeNet-5 neural network, achieves a recognition accuracy of 96.48% on the MNIST data set. These results demonstrate a promising optoelectronic strategy for advanced neuromorphic computing systems.
In this paper, the authors report a compact, quasi-monolithic optical distribution module (220 mm × 170 mm × 65 mm) developed toward field-deployable 87Rb atom gravimetry. The module combines a Zerodur substrate with a PR-20 piezoelectric rotation stage having a closed-loop angular resolution of 3.5 μrad. The stage drives one wedge in a compact double-wedge layout and provides local correction along a calibrated one-dimensional actuator trajectory. Without active correction, the Raman-path fiber-coupled power decreased to 42% of its 25°C baseline under a 10°C chamber condition; one-dimensional active correction recovered it to approximately 80%. In atom-interferometer operation under the same cold condition, 100 consecutive k-reversal scan pairs showed that the branch-averaged fitted fringe visibility increased from 15.65% to 29.28%, a 1.87-fold improvement. The controller performs local search followed by bounded setpoint maintenance on a calibrated monotonic branch. These results demonstrate optical-delivery stabilization during controlled 10°C–40°C thermal cycling and fringe-visibility recovery at 10°C, providing a compact route toward more robust transportable quantum sensors.
