Multimode interference (MMI) has been considered to be critical and investigated extensively in mode-locked laser based on single transverse mode systems, whereas there are few researches related to three-dimensional nonlinear dynamics within lasers. In this paper, we demonstrate all-fiber high-power spatiotemporal mode-locked (STML) laser by optimizing MMI filtering, where we find that the MMI filtering plays an important role in counteracting the coupling of high-order modes and improving output power of STML laser. The results under weak coupling condition when the length of graded-index multimode fiber (GIMF) is integral multiple of beat length show that the oscillator generates dissipative soliton pulses at 1036.86 nm with pulse width of 5.65 ps, and the slope efficiency of pump-signal is up to 10.3% with average power/energy of 215 mW/6 nJ, which is the highest among all-fiber STML lasers in normal dispersion regime. Besides, the multiple-soliton of STML, including multiple pulses and harmonic mode-locking can be observed in the experiment. Our work significantly broadens the dimensions of design for all-fiber high-power STML and makes them much more accessible for being put into applications.
A novel harmonic mode-locked fiber laser based on nonlinear multimode interference (NL-MMI) in a microfiber-assisted ultrafast optical switch is proposed in this Letter. The microfiber-assisted ultrafast optical switch can be obtained by tapering the splicing point of the graded-index multimode fiber (GIMF) and single-mode fiber, which not only helps to shorten the self-imaging period in GIMF to relax the strict requirement of NL-MMI on the length of multimode fiber, but also improves the harmonic order. In the experiment, with the waist diameter of ∼15 μm, the repetition rates of the fiber laser can be stably locked at 285 MHz, corresponding to the 16th-order harmonic mode-locking, with the pulse duration of 1.52 ps. Our results provide novel insight into the design of a high-repetition-rate laser and the application of microfibers in the modelocking device.
A tunable mode-locked all-fiber Yb-doped laser with a double offset-splicing step-index few-mode fiber (DOS-SIFMF) is demonstrated, to the best of our knowledge, for the first time. The structure of DOS-SIFMF, which constructs a micro Mach–Zehnder interferometer as a consequence of introducing offset splicing, has characteristics of both a saturable absorber and filter and is more accessible to obtain mode-locking operation in an all-normal dispersive region. The results of simulation show that interference with fewer modes is more reliable to acquire mode-locking operation of the fiber laser. The central wavelength, spectrum, and pulse widths are 1032 nm, 6.15 nm, and 28.8 ps, respectively. The output pulse in time and spectrum domains can be tuned in the range of 168.7 ps and 10.7 nm, respectively. This structure has effects of both mode-locking and filtering, showing potential application in communication and sensing. Furthermore, the influence on mode number to interference is generally discussed in the end.
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