Monolithically integrated 940†nm VCSELs on bulk Ge substrates.

This research successfully developed an independent Ge-based VCSEL epitaxy and fabrication technology route, which set the stage for integrating AlGaAs-based semiconductor devices on bulk Ge substrates. This is the second successful Ge-based VCSEL technology reported worldwide and the first Ge-based VCSEL technology with key details disclosed, including Ge substrate specification, transition layer structure and composition, and fabrication process. Compared with the GaAs counterparts, after epitaxy optimization, the Ge-based VCSEL wafer has a 40% lower surface root-mean-square roughness and 72% lower average bow-warp. After device fabrication, the Ge-based VCSEL has a 10% lower threshold current density and 19% higher maximum optical differential efficiency than the GaAs-based VCSEL.

25 Gb/s NRZ transmission at 85°C using a high-speed 940 nm AlGaAs oxide-confined VCSEL grown on a Ge substrate.

In this Letter, we present a comprehensive analysis of the high-speed performance of 940 nm oxide-confined AlGaAs vertical-cavity surface-emitting lasers (VCSELs) grown on Ge substrates. Our demonstration reveals a pronounced superiority of Ge-based VCSELs in terms of thermal stability. The presented Ge-VCSEL has a maximum modulation bandwidth of 16.1 GHz and successfully realizes a 25 Gb/s NRZ transmission at 85 ∘C. The experimental results underscore the significance and potential of Ge-VCSELs for applications requiring robust performance in high-temperature environments, laying the cornerstone for the future development of VCSEL devices.

LFVB-BioSLAM: A Bionic SLAM System with a Light-Weight LiDAR Front End and a Bio-Inspired Visual Back End.

Simultaneous localization and mapping (SLAM) is one of the crucial techniques applied in autonomous robot navigation. The majority of present popular SLAM algorithms are built within probabilistic optimization frameworks, achieving high accuracy performance at the expense of high power consumption and latency. In contrast to robots, animals are born with the capability to efficiently and robustly navigate in nature, and bionic SLAM algorithms have received increasing attention recently. Current bionic SLAM algorithms, including RatSLAM, with relatively low accuracy and robustness, tend to fail in certain challenging environments. In order to design a bionic SLAM system with a novel framework and relatively high practicality, and to facilitate the development of bionic SLAM research, in this paper we present LFVB-BioSLAM, a bionic SLAM system with a light-weight LiDAR-based front end and a bio-inspired vision-based back end. We adopt a range flow-based LiDAR odometry as the front end of the SLAM system, providing the odometry estimation for the back end, and we propose a biologically-inspired back end processing algorithm based on the monocular RGB camera, performing loop closure detection and path integration. Our method is verified through real-world experiments, and the results show that LFVB-BioSLAM outperforms RatSLAM, a vision-based bionic SLAM algorithm, and RF2O, a laser-based horizontal planar odometry algorithm, in terms of accuracy and robustness.

Cesium Lead Halide Perovskite Decorated Polyvinylidene Fluoride Nanofibers for Wearable Piezoelectric Nanogenerator Yarns.

Piezoelectric nanogenerators (PENGs) provide a viable solution to convert the mechanical energy generated by body movement to electricity. One-dimensional yarns offer a platform for flexible wearable textile PENGs, which can conform to body for comfort and efficient energy harvesting. In this context, we report a flexible piezoelectric yarn, assembled by one-step cocentric deposition of cesium lead halide perovskite decorated polyvinylidene fluoride (PVDF) nanofibers, on a stainless-steel yarn. Perovskite crystals were formed in situ during electrospinning. Our work demonstrates a nanofiber morphology in which perovskite crystals spread over the nanofiber, leading to a rough surface, and complementing piezoelectric nanocomposite formation with PVDF for superior stress excitation. We investigated how the halide anions of perovskite affect the piezoelectric performance of PENG yarns by comparing CsPbBr3 and CsPbI2Br. Effects of the perovskite concentration, annealing temperature, and deposition time on the piezoelectric properties of PENG yarns were investigated. Devices assembled with a single yarn of CsPbI2Br decorated PVDF nanofibers yield the optimal performance with an output voltage of 8.3 V and current of 1.91 µA in response to pressing from an actuator and used to charge capacitors for powering electronics. After aging in the ambient environment for 3 months, the device maintained its performance during 19,200 cycles of mechanical stresses. The excellent and stable electrical performance can be ascribed to the optimized crystallization of CsPbI2Br crystals, their complementing performance with PVDF, and formation of nanofibers with uniformity and strength. The flexibility of piezoelectric yarns enables them to be bent, twisted, braided, and woven for different textile integrations while harvesting energy from body movements, demonstrating the potential for wearable mechanical energy harvesting.