Broadband and stable linearly polarized mode converter based on polarization-maintaining fiber long-period grating.

• Long-period fiber grating based linearly polarized mode converter operating at a dispersion turning point has been demonstrated. Such mode converter can realize broadband mode conversion. • A broadband and controllable linearly polarized OAM modes generator using a single long-period fiber grating followed by a length of few-mode polarization-maintaining fiber has been demonstrated. • A simple approach was proposed to tunable the linearly polarized OAM mode, the phase difference of the two linearly polarized modes was continually turned by strain, the OAM mode can be smoothly tunable between ±1 order. We demonstrate a broadband and stable linearly polarized mode converter by inscribing long-period grating (LPG) in few-mode polarization-maintaining fibers (FPMFs). The operating wavelength of the mode converter at 1.0- and 1.5- μm waveband has been achieved by using PMF with different cut-off wavelengths. Theoretical and experimental demonstrated broadband linearly polarized mode conversion can be achieved with a maximum 10 dB bandwidth of 140- and 189- nm at 1.0- and 1.5- μm waveband respectively due to the turning point coupling mechanism. Then, we propose and demonstrate a controllable linearly polarized orbital angular momentum (LP-OAM) mode generator using a single LPG-based mode converter and a length of FPMF. The LP-OAM mode is produced by turning axial strain and can be smoothly switched between ± 1 order. Our all-FPMF based grating fabrication offers a new option towards a stable and broadband polarized mode converter and LP-OAM mode generator for application in a few-mode fiber laser and communication system. [ABSTRACT FROM AUTHOR]