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Visible-Wavelength-Tunable, Vortex-Beam Fiber Laser Based on a Long-Period Fiber Grating
IEEE Photonics Technology Letters  (IF2.468),  Pub Date : 2021-09-09, DOI: 10.1109/lpt.2021.3111191
Zhipeng Dong, Honggang Sun, Yimin Zhang, Jinhai Zou, Lixin Xu, Zhengqian Luo

In this letter, we report the first demonstration of a visible-wavelength-tunable, vortex-beam fiber laser based on a Sagnac-loop fiber filter and efficient long-period fiber grating. A 30 cm Pr 3+ /Yb 3+ -codoped ZBLAN fiber pumped by a 445 nm laser diode provides ~ 635 nm strong optical gain. A homemade dielectric mirror on the fiber end-facet and a Sagnac-loop fiber filter are used to build a wavelength-tunable fiber laser with a wavelength range of 633.89 to 636.02 nm. A self- fabricated long-period fiber grating acts as a mode converter in the cavity, and one-order vortex-beam including cylindrical vector beams (CVBs) and orbital angular momentum beams (OAMs) with a high mode purity are successfully obtained. Furthermore, we also measured the speckle contrast of the visible-wavelength fiber laser, and the speckle contrast is reduced by 17.13% through CVBs. This work could offer an effective approach to develop compact, wavelength-tunable vortex fiber lasers in the visible spectrum for applications to high-resolution imaging, laser display, visible light communications, and scientific research.