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.

Random lasers are a type of lasers that lack typical resonator structures, offering benefits such as easy integration, low cost, and low spatial coherence. These features make them popular for speckle-free imaging and random number generation. However, due to their high threshold and phase instability, the production of picosecond random lasers has still been a challenge. In this work, we have developed three dyes incorporating polymer optical fibers doped with various scattering nanoparticles to produce short-pulsed random fiber lasers. Notably, stable picosecond random laser emission lasting 600 ps is observed at a low pump energy of 50 µJ, indicating the gain-switching mechanism. Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level. When the intensity of the continuously pumped light reaches a specific value, the number of inversion populations in the “scattering cavity” surpasses the threshold rapidly. Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon. This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.

逐像元自适应增益成像系统通过在每个像元的电子链路中集成四档不同容积的积分电容，可以在确保高信噪比的前提下实现大动态范围的遥感成像需求。此成像系统在发射前测试时，由于甚低增益（ULG）的动态范围过大而实验室积分球能量有限，只能通过与低增益（LG）的比例系数递推来间接对ULG后半量程的输出特性标定；星载太阳定标器反射能量过大会导致高增益（HG）和中增益（MG）输出饱和也无法直接测定辐射定标系数，只可通过比例系数推定。提出一种星上增益比例系数测定的方案，分别利用四档增益的输出作为特征对实验图像分类，将不同成像目标的输出码值作为多个定标能级，利用最小二乘法线性拟合相邻增益输出后得到相邻增益的比例系数。此方案验证了实验室增益比例系数测定结果，同时在外场成像实验中用该方法计算得到的比例系数用于相邻两档增益中较低增益图像反演较高增益图像，结果与实际较高增益图像对比归一化均方误差大部分小于0.01、两图像结构相关系数基本在90%左右、数据相关系数达到90%。证明该方法测定的相邻两增益比例相关系数有较高准确性，在星上辐射定标时用于高增益辐射定标系数的递推求取有极大的可行性，解决了星上不能直接对HG、MG辐射定标的问题。

多芯超模光纤（MCSMF）的芯间距较小，多个芯子共同形成芯区支持多个超模传输，与普通单芯少模光纤相比，其具有较大的有效模场面积和较小的模式串扰，备受关注。MCSMF用于长距离传输时，与其相匹配的新型增益均衡放大器是实现信号中继并保持信号稳定传输的必要器件。文中提出了一种基于粒子群优化算法的19芯超模光纤增益均衡放大器，该光纤支持10个超模共同传输。通过粒子群算法分别优化各纤芯内掺铒浓度来降低不同超模的交叠积分因子，从而减小模式增益差（DMG）。结果表明，在包层泵浦条件下，最大DMG从1.33 dB （各纤芯均匀掺杂）降低至0.20 dB，在1 550 nm信号波长处10模式的平均增益为27.79 dB，且该放大器在整个C波段的增益平坦度低于1 dB。

通过FDTD仿真模拟计算，文中系统地研究了电流阻挡作用对GaN基蓝光激光器增益分布和光学性能的影响，发现回音壁激光模式主要在靠近微盘边缘1.5个波长范围谐振，因此，如果电流阻挡层面积太小，无法最大化减小激光器电流阈值；如果面积太大，回音壁激光模式与无增益区存在耦合效应，从而减少激光功率。另外，随着无增益区域向微盘边缘发生偏移，各个激光模式输出的峰值功率均下降，其中二阶模式峰值功率比一阶模式下降得更加显著，这主要是由于二阶模式分布范围更接近微盘中心区域。同时，进一步发现如果在微盘激光器的仿真模型中引入侧壁缺陷，则将导致边缘无法形成增益区，相比于二阶模式而言，一阶模式的发光功率随侧壁缺陷区域增加而下降的幅度更为显著，这主要是由于一阶模式分布范围更接近微盘边缘。

The dynamic gain of a few-mode erbium-doped fiber amplifier (FM-EDFA) is vital for the long-haul mode division multiplexing (MDM) transmission. Here, we investigate the mode-dependent dynamic gain of an FM-EDFA under various manipulations of the pump mode. First, we numerically calculate the gain variation with respect to the input signal power, where a mode-dependent saturation input power occurs under different pump modes. Even under the fixed intensity profile of the pump laser, the saturation input power of each spatial mode is different. Moreover, high-order mode pumping leads to a compression of the linear amplification region, even though it is beneficial for the mitigation of the differential modal gain (DMG) arising in all guided modes. Then, we develop an all-fiber 3-mode EDFA, where the fundamental mode of the pump laser can be efficiently converted to the LP₁₁ mode using the all-fiber mode-selective coupler (MSC). In comparison with the traditional LP₀₁ pumping scheme, the DMG at 1550 nm can be mitigated from 1.61 dB to 0.97 dB under the LP₁₁ mode pumping, while both an average gain of 19.93 dB and a DMG of less than 1 dB can be achieved from 1530 nm to 1560 nm. However, the corresponding signal input saturation powers are reduced by 0.3 dB for the LP₀₁ mode and 1.6 dB for the LP₁₁ mode, respectively. Both theoretical and experimental results indicate that a trade-off occurs between the DMG mitigation and the extension of the linear amplification range when the intensity profile of pump laser is manipulated.

基于SiC宽禁带半导体材料及器件，实现了SiC宽禁带器件与超高真空器件的混合兼容设计与制备，研制了一种新型的SiC基真空‑固态混合光电探测器，光敏面有效直径25 mm，器件电子轰击增益近200倍，响应信号半高宽4.5 ns。为真空‑固态混合光电探测器件理论研究与工程应用的深入推进奠定了基础。