High-order mode fiber laser based on few-mode fiber gratings

We propose and experimentally demonstrate a high-order mode fiber laser based on few-mode fiber gratings. The fiber laser has the structure of three sub-ring-cavities. LP01 mode, LP11 mode and LP21 mode can be obtained by different few-mode long-period fiber gratings. The reflection of LP01 mode, LP11 mode and LP21 mode can be realized by different few-mode fiber Bragg gratings. Therefore, the simultaneous lasing of LP01 mode, LP11 mode and LP21 mode at the same wavelength can be achieved. A few-mode fiber Bragg grating functions as a discrete filter. By adjusting a polarization controller, switchable output among single-, dual- and triple-wavelength lasing can be realized, and three wavelengths correspond to LP01 mode, the mixing of LP01 mode and LP11 mode, and LP11 mode. Therefore, the simultaneous lasing of different modes at the same wavelength, and the simultaneous lasing of different modes at different wavelengths can be achieved in this fiber laser, which can be applied to optical communication systems based on mode-division multiplexing-wavelength-division multiplexing.