基于光束扫描法的光纤预制棒折射率测试仪主要适用于直径和长度在一定范围内的圆柱形样品折射率分布的测试。提出一种套管辅助法可实现更短长度、更细直径和变直径样品的折射率测试。该方法将待测样品居中放置于一个尺寸符合测试要求的圆柱形套管内，并在套管内注入折射率匹配油，使其没过待测样品后按常规步骤进行测试。对比实验结果表明，套管辅助法与直接测量法的偏差与仪器的测量误差相当。采用套管法，获得了预制棒拉丝终止后变径区不同位置折射率的径向分布，可为拉丝过程的研究提供参考。

长距离侧面泵浦激光光纤在泵浦光注入、热管理、非线性抑制等方面具有天然优势，是实现高功率激光输出的有效途径。研制了（1+1）型长距离侧面泵浦激光光纤，采用1018 nm同带泵浦反向注入方式实现了17.4 kW激光输出，斜率效率为82.1%，3 dB线宽为1.3 nm，拉曼抑制比为37.8 dB。研究结果展示了长距离侧面泵浦光纤作为数十千瓦光纤激光放大器增益介质的巨大应用潜力。

A novel physical layer data encryption scheme using two-level constellation masking in three-dimensional (3D) carrier-less amplitude and phase modulation (CAP) passive optical network (PON) is proposed in this Letter. The chaotic sequence generated by Chua’s circuit model realizes two-level encryption of displacement masking and constellation rotation for 3D constellations. We successfully conduct an experiment demonstrating 8.7 Gb/s 3D-CAP-8 data transmission over 25 km standard single-mode fiber. With two-level constellation masking, a key space size of 2.1 × 10⁸⁵ is achieved to bring about high security and good encryption performance, suggesting broad application prospects in future short-range secure communications.