Abstract
Optical vortices, characterized by helical phase fronts, are usually generated outside the laser cavity using passive modulation methods. Here, we demonstrate an all-fiber laser to directly deliver mode-locked and continuous-wave vortex beams based on modulation of transverse modes in the two mode fiber. The mode couplers and reflectors for three schemes are long period fiber grating (LPFG) and fiber mirror, fiber taper and fiber Bragg grating, and LPFG and fiber Bragg grating, respectively. The laser is switchable between ±1 order vortex operations by tuning the intracavity polarization controller, and the optical vortex can directly work as an optical tweezer to manipulate rhenium diselenide nanosheets. The pulse duration at the mode-locked state is tunable from subpicoseconds to several picoseconds by spectral filters, and the maximum output power at the continuous-wave state exceeds 35 mW. The cost-effective all-fiber vortex laser is quite attractive for research of micromanipulation, spatiotemporal soliton, and optical communication.
Highlights
Modulated structured lights refer to light beams with modulated phase, intensity, or polarization in spatial domain.[1]
For scheme 1 based on long period fiber grating (LPFG) and fiber mirror, the fundamental mode should be fully converted into the vortex mode, and the pressure imposed on the LPFG is relatively high to get a large mode conversion efficiency
We have demonstrated a vortex laser based on the modulation of transverse modes in two mode fiber
Summary
Modulated structured lights refer to light beams with modulated phase, intensity, or polarization in spatial domain.[1]. The generation and evolution of vortex beams in fibers captured a great deal of research interest[25–28] due to its promising applications in fiber communication,[29] quantum entanglement,[2] and nonlinear fiber optics.[30]. Naidoo et al elucidated the formation mechanism of cylindrical vector beams and vortex beams from a continuous-wave laser based on the geometric phase control inside the cavity.[39]. Due to the superposition of multiple transverse modes in the fiber, the output laser has a spherical wave front and an irregular intensity distribution in spatial domain. We demonstrate mode-locked and continuouswave fiber lasers delivering switchable ±1 order vortex beam based on the mode modulation in two mode fibers (TMFs). The spatial distributions and temporal properties of optical vortices are quite stable, indicating that fiber lasers operate at the spatiotemporal mode-locked operation
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