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.
Bibliographical noteFunding Information:
This work was supported by the National Natural Science Foundation of China ( 62075124 , 61875117 ) and the National Key Research and Development Program of China (2020YFB1805800). Chen Jiang also acknowledges the China Scholarship Council for financial support.
- Dispersion turning point
- Long-period gratings
- Mode converter
- OAM mode generator
- Polarization-maintaining fibers