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.

We propose and experimentally demonstrate the programmable photonic radio frequency (RF) filters based on an integrated Fabry–Pérot laser with a saturable absorber (FP-SA). Owing to the high output power and the relative flatness spectrum of the FP-SA laser, only a waveshaper and an erbium-doped fiber amplifier (EDFA) were needed, which can greatly reduce the complexity of the system. The sinc filter employed 87 taps, representing a record-high tap number and resulting in a 3-dB bandwidth of 0.27 GHz and a quality factor of 148. Furthermore, Gaussian apodization enabled the out-of-band rejection of the filter to reach 34 dB and the center frequency to be finely tuned over a wide range, spanning from 4 to 14 GHz. These results indicate that the proposed scheme could provide a promising guideline for the photonic RF filters that demand both high reconfigurability and greatly reduced size and complexity.

构建了被动锁模光纤激光器的理论模型，通过数值仿真从时域和频域两个方面研究了高阶色散对输出脉冲特性的影响，在时域方面，三阶色散导致脉冲形状发生畸变，脉冲时域轮廓不对称，时域偏移等现象；在频域方面，三阶色散导致边带位置及强度发生变化。同时，研究发现四阶色散可以展宽脉冲，改变脉冲的边带强度。本文的研究结果对被动锁模掺镱光纤激光器的实际应用具有指导意义。

目前，飞秒激光脉冲因脉冲宽度窄和峰值功率高的特点被广泛运用在多种领域中。其中，色散管理光纤锁模激光器因其特有的腔内呼吸机制使输出的激光脉冲能量更高，光谱更宽、脉宽更窄。使用啁啾布拉格光纤光栅进行色散管理的光纤锁模激光器能够实现真正的全光纤结构，提升激光器的紧凑性和稳定性，因此基于啁啾布拉格光纤光栅进行色散管理的光纤锁模激光器具有更加实际的应用意义。采用数值模拟的方法，研究了基于啁啾布拉格光纤光栅进行色散管理的掺镱光纤锁模激光器中单模光纤在腔内的不同分布对脉冲动力学过程和输出脉冲参数的影响。系统分析了谐振腔内净色散值不同时，腔内单模光纤的分布对脉冲在腔内的动力学过程的影响。模拟结果表明，在腔内净色散值为负时，啁啾布拉格光纤光栅与增益光纤间的单模光纤越短，光纤激光器维持稳定单脉冲运行的最大泵浦强度更高且输出光谱更宽，从而能够获得脉宽更窄的去啁啾脉冲；腔内净色散值越接近零时，啁啾布拉格光纤光栅与增益光纤间的单模光纤长度对输出脉冲参数作用的影响越显著；腔内净色散值为正时，单模光纤在腔内的分布对输出脉冲影响逐渐减弱，优化单模光纤分布提升锁模激光器性能并不明显。最后，提出了一种通过改变单模光纤在腔内的分布来提高激光器输出性能的优化方法。

We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation. The laser generates 3.5 µm ultra-short pulses from an erbium-doped fluoride fiber by utilizing a dual-wavelength pumping scheme. Stable mode-locking is achieved at the 3.5 µm band with a repetition rate of 25.2 MHz. The maximum average power acquired from the laser in the mode-locking regime is 25 mW. The experimental results indicate that the carbon nanotube is an effective saturable absorber for mode-locking in the mid-infrared spectral region.

光频梳因频率等间隔、 波长稳定、 谱线线宽窄以及谱宽大等特性, 在高精度测量和计量中具有广泛的应用。 其中, 双光梳快速测量包括光谱测量、 绝对测距、 三维成像和超快异步光学采样等已成为研究热点之一。 近年来, 基于自由运行的单腔双光梳激光器的双梳光谱学系统由于具有结构简单、 测量范围大和精度高等优点而备受关注。 首先从时域和频域介绍了光频梳的特性和应用, 尤其介绍了双光梳测量的优势, 相较目前主流的稳频稳相锁模激光器、 电光调制等双光梳光源实现方案, 单腔双光梳激光器方案有望避免采用复杂的电子控制系统, 简化双光梳光源的结构、 体积和成本。 因此, 重点介绍了波长复用、 偏振复用、 空间复用和脉冲波形复用的单腔双光梳光纤激光器实现技术, 并对其基本原理、 性能参数和当前研究的进展以及目前发展中仍然存在的问题进行了分析; 同时对保偏光纤双光梳激光器的研究现状及其性能进行了总结。 接着, 重点介绍了双梳光谱学的测量原理, 回顾了现有光谱扩展技术, 并详细介绍了基于自由运行的单腔双光梳激光器的双梳光谱学应用案例, 包括掺铒光纤激光器所在的近红外波段以及其扩展到中红外和太赫兹波段的光谱探测。 最后, 总结了目前的单腔双光梳激光器的主要发展趋势, 包括进一步提高单腔型双光梳激光腔的重频稳定性、 降低共模噪声、 探索单腔双光梳系统在中红外以及太赫兹波段的应用, 推动单腔双光梳锁模光纤激光器的实用化。

稀土离子Tm³⁺/ Ho³⁺ 掺杂中红外2 μm波段超快激光由于广泛的应用前景成为近十余年来激光领域的研究热点之一。文中首先综述了稀土离子Tm³⁺/Ho³⁺掺杂固体/光纤2 μm波段超快激光锁模技术进展，包括主动锁模技术以及饱和吸收、克尔透镜、非线性偏振旋转、非线性光环形镜、非线性多模干涉等被动锁模技术；其次，结合激光增益介质及色散管理技术回顾了Tm³⁺/ Ho³⁺掺杂固体和光纤锁模激光脉冲宽度压缩进展；再次，总结了Tm³⁺/ Ho³⁺大能量/高功率超快激光技术及进展；最后，对2 μm波段超快激光发展趋势进行了总结和展望。