Five-wavelength-switchable all-fiber erbium-doped laser based on few-mode tilted fiber Bragg grating

We demonstrate a five-wavelength-switchable erbium-doped few-mode fiber laser based on a few-mode tilted fiber Bragg grating (TFBG). The TFBG was written in a few-mode graded-index fiber and has multiple resonance characteristics. Theoretical investigations reveal that these resonances originate from mode couplings among the LP01, LP11, and LP21 modes. Switchable five-wavelength lasing with different transverse modes is obtained by careful adjustment of the polarization controller and the lateral offset between the single-mode fiber (SMF) and the few-mode fiber (FMF) located before the TFBG in the laser cavity. This wavelength-switchable laser offers the advantages of a simple structure, stable lasing and ease of operation. The proposed structure can be potentially used in applications including communications, sensing and manipulation of microscopic particles.