Development of High-Precision NO2 Gas Sensor Based on Non-Dispersive Infrared Technology.

Increasing concerns about air quality due to fossil fuel combustion, especially nitrogen oxides (NOx) from marine and diesel engines, necessitate advanced monitoring systems due to the significant health and environmental impacts of nitrogen dioxide (NO2). In this study, a gas detection system based on the principle of the non-dispersive infrared (NDIR) technique is proposed. Firstly, the pyroelectric detector was developed by employing an ultra-thin LiTaO3 (LT) layer as the sensitive element, integrated with nanoscale carbon material prepared by wafer-level graphics technology as the infrared absorption layer. Then, the sensor was hermetically sealed using inert gas through energy storage welding technology, exhibiting a high detectivity (D*) value of 4.19 × 108 cm·âˆšHz/W. Subsequently, a NO2 gas sensor was engineered based on the NDIR principle employing a Micro Electro Mechanical System (MEMS) infrared (IR) emitter, featuring a light path chamber length of 1.5 m, along with integrated signal processing and software calibration algorithms. This gas sensor was capable of detecting NO2 concentrations within the range of 0-500 ppm. Initial tests indicated that the gas sensor exhibited a full-scale relative error of less than 0.46%, a limit of 2.8 ppm, a linearity of -1.09%, a repeatability of 0.47% at a concentration of 500 ppm, and a stability of 2% at a concentration of 500 ppm. The developed gas sensor demonstrated significant potential for application in areas such as industrial monitoring and analytical instrumentation.

Stably polarized 795 nm vertical-cavity surface-emitting lasers with anti-phase SiNx surface gratings.

795 nm vertical-cavity surface-emitting lasers (VCSELs) with dielectric surface gratings to control the output polarization are designed and fabricated. The calculated results demonstrate that a well-designed S i N x surface grating positioned on the surface of an anti-phase VCSEL structure enhances the reflectivity difference between the two polarization modes compared to a conventional GaAs surface grating, consequently resulting in a larger gain anisotropy in VCSELs and a high orthogonal polarization suppression ratio (OPSR). Characterization shows that a peak-to-peak OPSR of 30.3 dB is achieved at 85°C for 795 nm VCSELs with a S i N x surface grating of 5 µm in diameter and an oxide aperture of ∼4µm, demonstrating the effectiveness of the S i N x surface grating in polarization control for 795 nm VCSELs.

Circular-target-style bifocal zoom metalens.

Optical zoom plays an important role in realizing high-quality image magnification, especially in photography, telescopes, microscopes, etc. Compared to traditional bulky zoom lenses, the high versatility and flexibility of metalens design provide opportunities for modern electronic and photonic systems with demands for miniature and lightweight optical zoom. Here, we propose an ultra-thin, lightweight and compact bifocal zoom metalens, which consists of a conventional circular sub-aperture and a sparse annular sub-aperture with different focal lengths. The imaging resolutions of such single zoom metalens with 164 lp/mm and 117 lp/mm at magnifications of 1× and 2× have been numerically and experimentally demonstrated, respectively. Furthermore, clear zoom images of a dragonfly wing pattern have been also achieved using this zoom metalens, showing its distinctive aspect in biological imaging. Our results provide an approach for potential applications in integrated optical systems, miniaturized imaging devices, and wearable devices.

Silicon flower structures by maskless plasma etching.

Silicon nano/microstructures are widely utilized in the semiconductor industry, and plasma etching is the most prominent method for fabricating silicon nano/microstructures. Among the variety of silicon nano/microstructures, black silicon with light-trapping properties has garnered broad interest from both the scientific and industrial communities. However, the fabrication mechanism of black silicon remains unclear, and the light absorption of black silicon only focuses on the near-infrared region thus far. Herein, we demonstrate that black silicon can be fabricated from individual flower-like silicon microstructures. Using fluorocarbon gases as etchants, silicon flower microstructures have been formed via maskless plasma etching. Black silicon forming from silicon flower microstructures exhibits strong absorption with wavelength from 0.25 µm to 20 µm. The result provides novel insight into the understanding of the plasma etching mechanism in addition to offering further significant practical applications for device manufacturing.