An all-fiberized multi-wavelength mode-locked thulium-doped fiber laser (TDFL) based on fiber-optic Fabry–Perot interferometer (FPI) and nonlinear optical loop mirror (NOLM) has been presented. The fiber-optic FPI played the roles of wavelength selective filter and output mirror, which constructs by a single mode-hollow core-single mode fiber structure (SMF-HCF-SMF). A NOLM with wavelength-dependent cavity loss was employed to alleviate the mode competition in thulium-doped fiber and enabled the multi-wavelength mode-locking. With proper manipulation of the polarization controller and the pump power, besides the single-wavelength (~1948 nm) fundamental and high orders harmonic mode-locked operations, switchable dual-wavelength (1924.67/1949.16 nm and 1949.64/1972.68 nm) and stable three-wavelength (1924.80/1951.42/1972.14 nm) mode-locked operations are obtained. The multi-wavelength mode-locked TDFL exhibits a good stability with maximum peak power fluctuations of less than 0.5 dB in 2 h.

Multi‐color two‐photon microscopy imaging of live cells is essential in biology. However, the limited diffraction resolution of conventional two‐photon microscopy restricts its application to subcellular organelle imaging. Recently, we developed a laser scanning two‐photon non‐linear structured illumination microscope (2P‐NLSIM), whose resolution improved three‐fold. However, its ability to image polychromatic live cells under low excitation power has not been verified. Here, to improve the reconstruction super‐resolution image quality under low excitation power, we increased the image modulation depth by multiplying the raw images with the reference fringe patterns in the reconstruction process. Simultaneously, we optimized the 2P‐NLSIM system to image live cells, including the excitation power, imaging speed, and field of view. The proposed system could provide a new imaging tool for live cells.

In this paper, we have demonstrated a theta cavity passively Q-switched dual-wavelength fiber laser based on a multimode interference filter and a semiconductor saturable absorber. Relying on the properties of the fiber theta cavity, the laser can operate unidirectionally without an optical isolator. A semiconductor saturable absorber played the role of passive Q-switch while a section of single-mode-multimode-single-mode fiber structure served as an multimode interference filter and was used for selecting the lasing wavelengths. By suitably manipulating the polarization controller, stable dual-wavelength Q-switched operation was obtained at ~1946.8 nm and ~1983.8 nm with maximum output power and minimum pulse duration of ~47 mW and ~762.5 ns, respectively. The pulse repetition rate can be tuned from ~20.2 kHz to ~79.7 kHz by increasing the pump power from ~2.12 W to ~5.4 W.