We report on the generation of passive harmonic mode locking of a fiber laser using a microfiber-based topological insulator (TI) ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ saturable absorber (SA). The optical deposition method was employed to fabricate the microfiber-based TISA. By virtue of the excellent nonlinear optical property of the proposed TISA, the fiber laser could operate at the pulse repetition rate of 2.04 GHz under a pump power of 126 mW, corresponding to the 418th harmonic of fundamental repetition frequency. The results demonstrate that the microfiber-based TI photonic device can operate as both the high nonlinear optical component and the SA in fiber lasers, and could also find other applications in the related fields of photonics.

A tunable and switchable multiwavelength erbium-doped fiber ring laser based on what we believe to be a new type of tunable comb filter is proposed and demonstrated. By adjusting the polarization controllers, the dual-function operation of the channel-spacing tunability and the wavelength switching (interleaving) can be readily achieved. Up to 29 stable lasing lines with 0.4 nm spacing and 14 lasing wavelengths with 0.8 nm spacing in 3 dB bandwidth were obtained at room temperature. In addition, the lasing output, including the number of the lasing lines, the lasing evenness, and the lasing locations, can also be flexibly adjusted through the wavelength-dependent polarization rotation mechanism.

The pulse dynamics operating in dissipative soliton resonance (DSR) region is experimentally investigated in a fiber ring laser. With the increase of pump power, the pulse profile transit from sech-like to rectangular shape was observed. The generated pulse in DSR region exhibits the conventional soliton spectrum with sideband generation. The duration-tuning range of the rectangular pulse is up to the cavity roundtrip time. Particularly, during the process of pulse duration broadening it was found that the rectangular pulse would trap a weak pulse generated from cw background. The obtained results may be useful for better understanding the DSR phenomenon.

We reported, to the best of our knowledge, the first experimental evidence of the pulsating soliton with chaotic behavior in an ultrafast fiber laser. By virtue of a dispersive Fourier transformation method, the chaotic behavior of soliton pulsation is visualized by the fact that the mode-locked spectrum collapses abruptly in an unpredictable way during the pulsating process. The obtained results provide the experimental demonstration of the chaotic behavior in the pulsating soliton, which would also give some new insights into the soliton pulsation dynamics in dissipative systems.

Pulsating behavior is a universal phenomenon in versatile fields. In nonlinear dissipative systems, the solitons also pulsate under proper conditions and show many interesting dynamics. However, the pulsation dynamics are generally concerned with single-soliton cases. Herein, by utilizing real-time spectroscopy technique, namely, dispersive Fourier-transform (DFT), we reveal the distinct dynamical diversity of pulsating solitons in a fiber laser. In particular, the weak to strong explosive behaviors of pulsating solitons, as well as the rogue wave generation during explosions are observed. Moreover, the concept of soliton pulsation is extended to the multi-soliton case. It is found that the simultaneous pulsations of energy, separation and relative phase difference could be observed for solitons inside the molecule, while the pulsations of each individual in a multi-soliton bunch could be regular or irregular. These findings will shed new insights into the complex nonlinear behavior of solitons in ultrafast fiber lasers as well as dissipative optical systems.

We propose and numerically investigate a photonic crystal fiber (PCF) based on As₂S₃ for supporting the orbital angular momentum (OAM) modes up to 26. The designed PCF is composed of four well-ordered air hole rings in the cladding and an air hole at the center. The OAM modes can be well separated due to the large effective index difference of above 10⁻⁴ between the eigenmodes and maintain single-mode condition radially. In addition, the dispersions of the modes increase slowly with wavelengths, while the confinement loss keeps as low as 10⁻⁹ dB/m. The proposed PCF increases the supported OAM modes which could have some potential applications in short-distance, high-capacity transmission.