We propose and demonstrate a low-threshold single-wavelength all-fiber laser generating cylindrical vector beams using a few-mode fiber Bragg grating. Both radially and azimuthally polarized beams have been generated with very good modal symmetry and polarization purity higher than 94%. The radially and azimuthally polarized modes can be switched by simply adjusting the polarization controllers built in the fiber laser cavity. This fiber laser operates at a single wavelength of 1053 nm with a 3 dB linewidth of less than 0.02 nm, signal-to-background ratio of more than 55 dB, and a threshold as low as 16 mW. A new method for the polarization purity measurement is also proposed.

We report the generation of ultrawide tunable square-wave pulse in an erbium-doped mode-locked fiber laser. The pulse width can be tuned in an ultrawide range of more than 1700 ns by simply increasing the pump power. The pulse-width tuning is $5.1\mathrm{ns}/\mathrm{mW}$. To the best of our knowledge, this is the widest pulse-width tuning range of any square-wave pulse in an all-fiber passively mode-locked fiber laser. Experimental results show that the fiber nonlinearity plays an important role in the tuning range of the output pulse width. The high nonlinearity helps to increase the tuning range of the pulse width.

We report a fiber laser design that is capable of producing switchable transverse modes through wavelength tuning. The transverse mode switching is realized by exploiting the particular transverse mode-wavelength association characteristics of the few-mode fiber Bragg grating. Different transverse mode outputs with high spatial mode quality can be obtained by adjusting the oscillating wavelength with a tunable filter within the fiber laser cavity. For each of the spatial mode outputs, the laser operates at the corresponding single wavelength with narrow linewidth. Through adding polarization controllers in the laser cavity, output modes with cylindrical vector polarization are also realized.

We have proposed and demonstrated a figure-8 dual-pump passively mode-locked fiber laser to generate square-wave pulse tunable by both width and amplitude. Just by simply adjusting the power of the pumps, both the amplitude and width of the output square-wave pulse can be tuned independently and continuously. One pump is used to tune the output pulsewidth while the other is used to tune amplitude.

We proposed and demonstrated an all-fiber laser to generate cylindrical vector beam. A pair of fiber-based collimators was used to select the cylindrical vector beam operating. The radially and azimuthally polarized modes can be switchable just by applying pressure to a section of fiber in our fiber laser system. A 70 cm long Yb-doped fiber was used as gain medium and the lasing wavelength was around 1030 nm.

We propose and demonstrate a radially polarized mode-locked fiber laser through the use of a figure-8 cavity in combination with cascade fiber Bragg gratings (FBGs). The mode-locked laser emits rectangular pulses with width tunable from 2.8 to 23 ns under an increasing pump power at 1056.3 nm with 0.2-nm 30-dB linewidth. A polarization purity as high as 96% for the output transverse mode has been achieved simultaneously.