Third-order orbital angular momentum pulse generation from a passively Q-switched fiber laser

• Main Authors: Du, C. (Author), Gao, S. (Author), Li, W. (Author), Li, Z. (Author), Liu, W. (Author), Tu, J. (Author), Wen, T. (Author), Xiao, R. (Author), Zhang, B. (Author), Zhou, J. (Author)
• Format: Article
• Language: English
• Published: Optica Publishing Group (formerly OSA) 2022
• Subjects: All fiber; Angular momentum; Cross structures; Diffraction gratings; Fiber lasers; Fibers; Graphene; Long-period fibre gratings; Optical tweezers; Orbital angular momentum; Passively Q-switched; Passively Q-switched lasers; Pulse generation; Q switched lasers; Q switching; Q-switched fiber lasers; Refractive index; Refractive-index modulation; Saturable absorbers; Third order
• Online Access: View Fulltext in Publisher

 We propose and demonstrate an all-fiber passively Q-switched laser generating a third-order orbital angular momentum (OAM) pulse by introducing a few-mode long-period fiber grating (LPFG) into the laser cavity. The LPFG with asymmetric cross structure and strong refractive index modulation overcomes the coupling issue between the fundamental and the third-azimuthal-order (LP31 or OAM3) modes and realizes their direct conversion. A homemade graphene-based saturable absorber is used to realize Q-switched operation. The laser operates at a center wavelength of 1548.2nm, with a 3 dB spectral bandwidth of 0.4nm, and the OAM+3 and OAM−3 beams can achieve the purity of 90.0% and 90.2%, respectively. This all-fiber Q-switched laser has simple and compact structure and high purity of OAM±3 beams, which has potential applications in the fields of optical tweezers and material processing. © 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement Journal © 2022