A 2.1 μm, high energy square-wave noise-like pulse (NLP) in an all-fiber Ho-doped fiber laser is proposed, which consists of an oscillator and a single-stage amplifier. In the figure-of-9 oscillator, mode-locking is achieved based on the nonlinear amplifying loop mirror, employing a long gain fiber to provide sufficient gain in 2.1 μm band and optimizing the cavity length to obtain maximum pulse energy output. With appropriate pump power and polarization state, the oscillator emits a 175.1 nJ square-wave NLP with center wavelength of 2102.2 nm and spike width of 540 fs. The 3-dB spectral width and pulse envelope width are 11.2 nm and 6.95 ns, respectively. The single-stage amplifier employs a bi-directional pump scheme. After amplification, 5.8 W NLP with a slope efficiency of 56.8% is obtained. The pulse energy of NLP is scaled to 1.52 μJ, which is the highest pulse energy of NLP at 2.1 μm to the best of our knowledge. The obtained high-energy square-wave NLP-fiber laser has great potential in mid-infrared laser generation.

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Pulse evolution and multi-pulse state of coherently coupled polarization domain walls (PDW) is experimentally demonstrated in a novel fiber ring laser. Versatile pulse shapes benefit by wide range moving of PDW in the weakly birefringent fiber. The 8.6 m short-cavity structure is more compact and accessible based on a 976 nm pump with nearly zero negative dispersion (-0.0002 ps2). Besides, multi-pulse patterns such as PDW splitting, harmonic mode-locking, and periodic soliton collision are also observed under larger net negative dispersion (-3.09 ps2) and 151m-longer cavity. This is the first demonstration of coherently coupled PDW in a fiber laser using a bandpass filter and the formation of coherently coupled PDW is ascribed to the BPF’s force filtering.

We report the demonstration of a mid-infrared (MIR) supercontinuum (SC) laser delivering a record-breaking average output power of more than 40 W with a long wavelength edge up to 3.5 μm. The all-fiberized configuration was composed of a thuliumdoped fiber amplifier system emitting broadband spectrum covering 1.9-2.6 μm with pulse repetition rate of 3 MHz, and a short piece of germania fiber. A 41.9 W MIR SC with a whole spectrum of 1.9 to 3.5 μm was generated in a piece of 0.2-m-long germania fiber, with a power conversion efficiency of 71.4%. For an even shorter germania fiber (0.1 m), an SC with even higher output power of 44.9 W (corresponding to a conversion efficiency of 76.5%) was obtained, but the energy conversion towards long wavelength region was slightly limited. A continuous operation for 1 hour with output power of 32.6 W showed outstanding power stability (RMS 0.17%) of the obtained SC laser. To the best of the

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