Controllable mode emission from all-fiber laser based on polarization rotation technology and its application in bending sensing

We demonstrate a simple and compact all-fiber structure that can generate tunable fiber modes, including LP01, LP11 and OAM modes. The offset splicing between a single-mode fiber (SMF) and a multi-mode fiber (MMF) is used to excite LP11 mode in the MMF from LP01 mode in the SMF. The polarization controller (PC) is used to control the incident angle of the LP11 mode from the MMF into the polarization-maintaining fiber (PMF). The LP11 mode and OAM+1/OAM−1 mode can be generated at a specific incident angle (45°/135°) in the experiment. In addition, the designed laser has been used to detect the fiber bending degrees. It is found experimentally that the changes in the strength of the two lobes of the output LP11 mode have good linearity in the range of bending diameters from 15 to 35 mm. •LP01, LP11 and OAM modes can be tunably generated by the laser.•OAM modes are generated by polarization rotation technology.•OAM modes have high mode purity.•PMF fiber in the laser responds well to bending.