We report a Yb-doped mode-locked fiber laser based on a nonlinear amplifying loop mirror (NALM), which is all-normal-dispersion (ANDi), and allows the output wavelength to be tunable. The laser can generate a stable femtosecond dissipative soliton with a maximum output power of 196 mW. Its repetition rate is 112.4 MHz, and the final pulse duration is 236 fs. By adjusting the angle of the reflective diffraction grating, the mode-locked fiber laser was realized to tune the output with a tuning range of 54 nm from 1011.8 nm to 1065.6 nm. To the best of our knowledge, this is the widest tuning range of an ANDi Yb-doped mode-locked fiber laser based on NALM.

Frequency detuning of mode-locked fiber lasers displays many remarkable nonlinear dynamical behaviors. Here we report for the first time the evolution of pulses from mode-locking through period pulsation to Q-switched mode-locking for three fundamental cases. Our experiments are performed in a hybrid actively and passively amplitude-modulated all-fiber polarization-maintaining mode-locked fiber laser, where the amplitude modulation frequency artificially deviates from the fundamental frequency of the cavity. We design and numerically simulate the laser with coupled Ginzburg–Landau equations. The experimentally observed dynamics of the mode detuning process is discussed with the assistance of the fitted model and numerical simulations, showing the generalizability of the optical mode detuning variation process. Our work provides fundamental insights for understanding perturbations in nonlinear optical resonant cavities and expands the ideas for studying chaotic path theory in hybrid mode-locked fiber lasers.

基于光纤环形激光器，设计出由三端口环形器、偏振控制器、未泵浦保偏掺镱光纤和光纤布拉格光栅组成的滤波器件作为高精度滤波器对谐振腔内的模式个数进行抑制，通过调谐偏振控制器，在保偏掺镱光纤内形成的梳状光谱和动态光栅，实现了窄线宽、单、双波长可切换单频掺镱光纤激光器。单波长运行时，在1064.37 nm处测得激光器输出线宽346 Hz，光信噪比大于50 dB，30 min内该激光器波长及功率的不稳定性均在0.01 nm和0.2 dB范围内。通过调节偏振控制器，单波长和双波长可以实现互相切换，双波长分别位于1064.156 nm和1065.236 nm。该技术为超窄线宽激光器的双波长输出提供了新的途径。

研究了一种基于非线性光纤环形镜“8”字形谐振腔结构的波长可调谐被动锁模掺铒光纤激光器，该激光器通过将偏振控制器加在耦合比为30/70的2×2光纤耦合器首尾相连的环内，在整个谐振腔的右端搭建了一个Sagnac环形滤波器。当泵浦功率为270 mW时，锁模光纤激光器输出了中心波长为1 555.7 nm的传统孤子，其光谱的3-dB带宽为4.2 nm，重复频率为21.1 MHz，信噪比为68 dB，脉冲宽度为0.759 ps。此外，在不改变腔内其他器件的情况下只增加泵浦功率，实现了锁模光纤激光器的连续可调谐，中心波长的调谐范围为1.5 nm；在增加泵浦功率到360 mW时，调节偏振控制器出现了松束缚态孤子。

报道了一种基于非线性放大环形镜的“8”字形腔波长可调谐锁模掺镱光纤激光器。当泵浦功率为240 mW时，光纤激光器输出中心波长在1 064.1 nm处的耗散孤子，其光谱3 dB带宽为7.7 nm，重复频率为18.8 MHz，输出光信噪比高达71.2 dB，脉冲宽度为867 fs。分别通过调节偏振控制器和泵浦功率实现了锁模光纤激光器在1 032.8~1 065.1 nm以及1 037.4~1 041.9 nm内调谐输出。探究了不同锁模状态下的光谱与脉冲特性，获得了时间带宽积接近傅里叶变换极限的高斯型脉冲。该光纤激光器结构简单，易于调谐，稳定性好，可为实现波长调谐、耗散孤子锁模提供技术参考。

We reported a wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on the intracavity loss tuning brought by the bent optical fiber. The bidirectional cavity structure achieved the self-sweeping effect due to the appearance of the dynamic grating in the active fiber with the spatial hole burning effect. Under this, a section of fiber was bent into a circle for adjusting the loss of the cavity. With a descending diameter of bent fiber circle, the sweeping range moves to the shorter wavelength and covers a wide range from 1055.6 to 1034.6 nm eventually. Both the initial wavelength of self-sweeping regime and the threshold of the fiber laser show exponential correlation with the diameter of the circular fiber. Our work provides a compact and low-cost way to achieve the broad wavelength-flexible self-sweeping operation.