Gallium nitride (GaN) has widespread applications in the semiconductor industry because of its desirable optoelectronic properties. The fabrication of surface structures on GaN thin films can effectively modify their optical and electrical properties, providing additional degrees of freedom for controlling GaN-based devices. Compared with lithography-based techniques, laser processing is maskless and much more efficient. This paper shows how surface micro-nano structures can be produced on GaN thin films using 355 nm nanosecond laser irradiation. The effects of the laser pulse energy, number of pulses, and polarization direction were studied. It was found that distinct micro-nano structures were formed under different irradiation conditions, and their geometries and elemental compositions were analyzed. The results indicate that different types of surface micro-nano structures can be produced on GaN thin films in a controllable manner using 355 nm nanosecond laser irradiation. The results of our study provide valuable guidance for the surface modification of GaN-based optoelectronic devices.Gallium nitride (GaN) has widespread applications in the semiconductor industry because of its desirable optoelectronic properties. The fabrication of surface structures on GaN thin films can effectively modify their optical and electrical properties, providing additional degrees of freedom for controlling GaN-based devices. Compared with lithography-based techniques, laser processing is maskless and much more efficient. This paper shows how surface micro-nano structures can be produced on GaN thin films using 355 nm nanosecond laser irradiation. The effects of the laser pulse energy, number of pulses, and polarization direction were studied. It was found that distinct micro-nano structures were formed under different irradiation conditions, and their geometries and elemental compositions were analyzed. The results indicate that different types of surface micro-nano structures can be produced on GaN thin films in a controllable manner using 355 nm nanosecond laser irradiation. The results of our study provide valuable guidance for the surface modification of GaN-based optoelectronic devices.

针对小尺寸无人机目标检测精度低, 且深层网络的参数量大、内存占用高等问题, 提出一种基于改进YOLOv5的无人机检测方法。首先, 调整了YOLOv5多尺度预测层的个数, 裁剪掉冗余网络层, 有效减少网络参数量, 提高无人机检测速度; 其次, 通过在特征提取阶段引入多个不同采样率的空洞卷积, 增强小目标的多尺度细节特征提取能力; 最后, 在多尺度特征融合阶段引入注意力机制, 将深层特征进行通道加权后再与浅层特征进行高效融合, 增强小目标特征表达能力。实验表明, 改进的YOLOv5模型在自制数据集上mAP达到了99.02%, 对于小尺寸的无人机目标, 具有更好的检测效果。相较于改进前网络, 检测速度提高了10.3%, 内存开销节约了65%, 降低了对设备计算和存储能力的要求, 更加有利于无人机检测系统的工程部署和实际应用。

We propose a third-order intermodulation distortion (IMD3) compensation scheme based on the bidirectional modulation of 2-Ch phase modulator (PM). We realize the destructive combination of IMD3 by using different modulation efficiencies and appropriately adjusting the input optical power ratio to satisfy a fixed relationship with modulation efficiency. The primary advantage of this scheme is that out-of-phase IMD3 is introduced using only one 2-Ch PM, thereby resulting in the cancellation of IMD3. Up to 27-dB suppression in IMD3 is experimentally demonstrated—a feature that will be useful in low-distortion analog optical transmission.