Mode field switching in narrow linewidth mode-locked fiber laser

Acousto-optic interaction can be used for ultrafast optical field control in passively mode-locked fiber lasers. Here, we propose the use of an intracavity acousto-optic mode converter (AOMC) with combination of a few-mode fiber Bragg gratings (FM-FBG) to achieve narrow linewidth mode-locked pulse output with switchable transverse mode and wavelength in a ring fiber laser. Due to the selectivity of the FM-FBG to the input mode, the output mode and wavelength can be adjusted in the mode-locked fiber laser based on a semiconductor saturable absorption mirror. In experiments, by adjusting the acoustic frequency imposed in the AOMC, the wavelength of mode-locked pulses was switched from 1551.52 nm to 1550.21 nm, retaining the repetition rate of 12.68 MHz. At the same time, the mode conversion from the LP01 to the LP11 mode in the FM-FBG transmission port was achieved. This laser may find application in mode-division multiplexing systems.

Automated summary

In this paper, a method combining FM-FBG and AOMC is proposed to achieve narrow linewidth mode-locked pulse output with adjustable transverse mode and wavelength in a fiber laser. The results of experiments show that by adjusting the acoustic frequency in AOMC, the wavelength of mode-locked pulses can be switched and mode conversion can be achieved. This laser may find applications in mode-division multiplexing systems.