Overview: In order to achieve the measurement of gravitational wave signals in the millihertz frequency band, the space-based gravitational wave detection projects such as LISA, TianQin, and Taiji projects, which are based on laser interference systems, require the hardware noise floor of the interferometers to be lower than the interstellar weak light shot noise limit. This imposes stringent engineering specifications on the optical-mechanical design and the corresponding interferometer payload. This paper approaches the issue from the perspective of detection mode selection and derives the expressions of readout noise and stray light noise in the interference signal under the single detector mode and the balanced mode. Furthermore, a detailed discussion is provided on the weak-light interference process of the scientific interferometer. The results demonstrate that the balanced mode is capable of suppressing the interference phase noise caused by laser power fluctuations and backscattered stray light across multiple orders of magnitude. However, the suppression capability is constrained by the unequal splitting property of the beam combiner. To address this, a relative gain factor is introduced to compensate for the unequal splitting property of the beam combiner. Further analysis reveals that electronic gain compensation can only eliminate the impact of unequal splitting on one of the two noises rather than both simultaneously. Therefore, a balance must be struck in selecting gain compensation between the suppression of laser power fluctuation noise and stray light noise. Even with this consideration, the balanced mode still offers significant noise suppression capabilities at a magnitude difference, thus potentially reducing the engineering requirements for laser power fluctuations and telescope backscattered stray light.

An approach for frequency division of an optical pulse train (OPT) based on an optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. When the OPT is injected into the OEO, a microwave signal with a frequency equaling fractional multiples of the repetition rate of the OPT is generated. This signal is then fed back to the OEO, maintaining its oscillation, while simultaneously serving as the control signal of a Mach–Zehnder modulator (MZM) in the OEO. The MZM acts as an optical switch, permitting specific pulses to pass through while blocking others. As a result, the repetition rate of the OPT is manipulated. A proof-of-concept experiment is carried out. Frequency division factors of 2 and 3 are successfully achieved. The phase noises of the OPT before and after the frequency division are investigated. Compared to previously reported systems, no external microwave source and sophisticated synchronization structure are needed.

光学下变频技术可将宽频带内全部电磁信号同时下变频到低频区间进行接收，是一种新型宽频带电磁环境快速接收技术。但是，获取的光学下变频信号中包含源个数未知、带宽不同的多种信号，现有信号分离方法需要获知源信号的个数，且无法同时分离窄带信号和宽带信号。为实现对光学下变频信号的自动分离，提出了一种基于变分模态分解（VMD）自适应模态重组的光学下变频信号分离方法。通过频谱分割因子和频谱包络检测，对光学下变频信号的VMD过分解模态进行自动重组和信号重组模态提取，实现光学下变频信号分离。对于包含普通脉冲信号、宽带码分多址（WCDMA）信号和线性调频脉冲信号的光学下变频信号，可自动实现对三种信号的分离，且与原信号的相似系数均高于0.97。实验结果表明，所提及方法在分离光学下变频信号时无需获知源信号的个数，并能同时分离具有不同带宽的多种源信号。

电源变换系统中功率器件如MOSFET和IGBT开关管的高速切换将产生高幅值和宽频段的电磁干扰，是电动车辆最为常见也无法避免的电磁干扰源。同时，互连线缆是机电设备传递信号和能量的载体，是实现设备功能不可或缺的组成部分，线缆的天线效应使其成为设备产生电磁干扰的主要途径，是系统电磁兼容问题的主要根源之一。为了分析高压电源变换系统对低压控制系统的电磁耦合，以某典型地面装备电源变换系统IGBT开关管产生的脉冲宽度调制波（PWM波）作为电磁干扰源，以实装线缆作为分析对象，构建高低压线缆串扰模型，仿真分析不同线缆对地距离、线缆间距条件下单线、屏蔽线、双绞线等多类低压线缆的近端串扰电压，得出低压线缆的抗干扰性，为系统线缆的布线提供指导。

提出融合变分模态分解（VMD）和自编码器的预测方法，将温升特性曲线分解成若干个子信号分量，其中包含高频的波动量、中间量和低频的趋势量，然后利用自编码器对每个分量进行预测，最后将分量的预测值相加，从而实现对PIN二极管温升特性曲线的精准预测。通过与多种机器学习方法的对比验证了结合VMD分解可有效提升预测精度，同时也验证了自编码器在特性曲线拟合上的优势。

激光弯曲成形技术常用的激光类型是点激光，在温度梯度机理的作用下单次成形角度有上限，在3°左右。为了增大点激光单次成形角度，提高成形效率，本文以不锈钢304板为对象，通过试验对比探索了将圆振荡模式应用于激光弯曲成形中以提高弯曲角方法的可行性；并且借助于三维视觉传感器测量板件在圆振荡激光束弯曲成形过程中的动态响应，从余热效应、吸收率等角度分析其弯曲成形机理。对比试验结果显示，在激光能量密度较高的情况下，圆振荡模式确实可以明显提高工件的弯曲角，增长率在60%左右。同时，三维视觉传感器的测量结果显示出了板件在成形过程中的复杂形变与角度变化过程：板件在长度与宽度方向上均产生了塑性变形，长宽形变比约为10∶1；单次扫描成形板件弯曲角增长过程呈现不同的增长曲线；多次扫描成形弯曲角分布不均衡。此外，板件厚度也逐渐增加，热影响区微观晶粒得到细化。为进一步理解圆振荡激光束弯曲成形过程与机理提供了试验支撑。

A low-numerical-aperture (NA) concept enables large-mode-area fiber with better single-mode operation ability, which is beneficial for transverse mode instability and nonlinear effects suppression. In this contribution, we reported a high-power fiber amplifier based on a piece of self-developed large-mode-area low-NA fiber with a core NA of 0.049 and a core/inner cladding diameter of 25/400 µm. The influence of the pump wavelength and fiber length on the power scaling potential of the fiber amplifier is systematically investigated. As a result, an output of 4.80 kW and a beam quality factor of ∼1.33 were finally obtained, which is the highest output power ever reported in a fiber amplifier exploiting the low-NA fiber. The results reveal that low-NA fibers have superiority in power scaling and beam quality maintenance at high power levels.

All-fiber few-mode erbium-doped fiber amplifiers (FM-EDFAs) with isolation and wavelength division multiplexers (IWDMs) have been developed to enable flexible pumping in different directions. The FM-EDFA can achieve >30 dB modal gain with <0.3 dB differential modal gain (DMG). We experimentally simulate the DMG performance of a cascade FM-EDFA system using the equivalent spectrum method. The overall DMG reaches 1.84 dB after 10-stage amplification. We also build a recirculating loop to simulate the system, and the developed FM-EDFA can support transmission up to 3270 km within a 2 dB overall DMG by optimizing the few-mode fiber length in the loop.