Optical chaos communication and key distribution have been extensively demonstrated with high-speed advantage but only within the metropolitan-area network range of which the transmission distance is restricted to around 300 km. For secure-transmission requirement of the backbone fiber link, the critical threshold is to realize long-reach chaos synchronization. Here, we propose and demonstrate a scheme of long-reach chaos synchronization using fiber relay transmission with hybrid amplification of an erbium-doped fiber amplifier (EDFA) and a distributed fiber Raman amplifier (DFRA). Experiments and simulations show that the hybrid amplification extends the chaos-fidelity transmission distance thanks to that the low-noise DFRA suppresses the amplified spontaneous emission noise and self-phase modulation. Optimizations of the hybrid-relay conditions are studied, including launching power, gain ratio of DFRA to EDFA, single-span fiber length, and number of fiber span. A 1040-km chaos synchronization with a synchronization coefficient beyond 0.90 is experimentally achieved, which underlies the backbone network-oriented optical chaos communication and key distribution.

高功率高能量飞秒光纤激光系统通常采用主振荡器加功率放大器结构。在放大飞秒脉冲时，非线性效应是制约脉冲能量的主要因素。基于传统啁啾脉冲放大技术的光纤激光系统虽然能够产生能量在1 mJ量级的飞秒脉冲，但是所产生的脉冲通常在200 fs以上，无法直接满足能量要求较低（1~100 µJ范围之内）、脉冲宽度却更短（60 fs以下甚至更短）的应用需求。与啁啾脉冲放大技术通过展宽脉冲而减少非线性相移相反，非线性放大故意保持脉冲的宽度在皮秒量级从而积累大量的非线性相移，导致放大后脉冲的光谱展宽为输入光谱的数倍，经过传统光栅对压缩后能够产生60 fs以下的近变换极限脉冲。本文主要以掺镱光纤放大系统为例，重点介绍自相似抛物线脉冲放大、预啁啾管理放大、增益管理放大和非线性分脉冲放大四种非线性光纤放大技术的工作原理、发展现状以及未来趋势。将提出的预啁啾管理分脉冲放大与多路相干合成相结合，有望产生重复频率1 MHz、平均功率超过1 kW、脉冲能量1 mJ左右的亚50 fs脉冲。这种千瓦级高重复频率、高能量飞秒脉冲源在基础科学、激光加工等领域中具有潜在的应用。

利用层状半导体β相硒化铟作为可饱和吸收体，在掺镱光纤激光器中实现稳定的调Q及锁模运转。经测量该可饱和吸收体在1 μm波段调制深度及非饱和损耗分别为47%及20%。将可饱和吸收体插入掺镱光纤激光器中，可获得53.42 kHz到217 kHz重频可调的调Q脉冲。其最窄脉冲宽度为630 ns，最大单脉冲能量为47.9 nJ。优化激光谐振腔后可进一步实现稳定的锁模输出，其重频为10.82 MHz，最大输出功率为51.2 mW，最大单脉冲能量为4.7 nJ。实验证明了β相硒化铟作为可饱和吸收体在近红外超快非线性光学方面的潜力。

使用一种新型有机材料马来酸掺杂聚苯胺作为可饱和吸收体，在掺铒全光纤激光振荡器中实现稳定的调Q运转。实验中，采用双臂探测法测得该材料的调制深度和可饱和吸收强度分别为13.9%和0.336 MW/cm²，将其以薄膜三明治形式插入到光纤谐振腔中，最终获得了重复频率从33.78 kHz到87.01 kHz的范围内可调，最窄脉冲宽度为2.29 μs，最大单脉冲能量为54.64 nJ的稳定调Q脉冲输出。马来酸掺杂聚苯胺可以被认为是脉冲光纤激光器应用及其它光电器件的良好候选者。

We report Q-switched and mode-locked erbium-doped all-fiber lasers using ternary ReS2(1 x)Se2x as saturable absorbers (SAs). The modulation depth and saturable intensity of the film SA are 1.8% and 0.046 MW/cm2. In Q-switched mechanism output, the pulse was centered at 1531.1 nm with maximum pulse energy and minimum pulse width of 28.29 nJ and 1.07 μs, respectively. In mode-locked operation, the pulse was centered at 1561.15 nm with pulse width of 888 fs, repetition rate of 2.95 MHz, and maximum pulse energy of 0.275 nJ. To the best of our knowledge, this is the first report on the mode-locked Er3+-doped fiber laser using ternary transition metal dichalcogenides. This work suggests prospective 2D-material SAs can be widely used in versatile fields due to their attractive optoelectronic and tunable energy bandgap properties.

We experimentally demonstrated a diode-pumped Kerr-lens mode-locked femtosecond laser with a Yb:CaYAlO₄ crystal as the gain medium. Pulse duration as short as 33 fs was obtained directly from the oscillator at a repetition rate of 115 MHz. The central wavelength was at 1059 nm with a spectral bandwidth of 49 nm. These are, to the best of our knowledge, the shortest pulses generated from a Yb:CaYAlO₄ oscillator.