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In this paper, the fibers with Yb 3? /Ho 3? codoped air cladding are fabricated by the plasma nonchemical vapor deposition method with the stack-capillarydraw technique for the first time to our knowledge. By the excitation at 975 nm, the fluorescence and up-conversion emission properties of these fibers are experimentally investigated. The mechanism of up-conversion emission is analyzed. The results show that such a fiber fabricated by using the plasma non-chemical vapor deposition method can be used as the potential material for the fiber laser at the visible and infrared spectral regions.

A helical Yb3+-doped three-core microstructure fiber (YTMF) amplifier is proposed in this paper, so as to solve the problem of generation and transmission of the orbital angular momentum (OAM) beams. The fiber is composed of three Yb3+-doped cores with a regular triangle shape and a longitudinal helical structure. The experimental results show that the 1064nm laser can be amplified due to the fluorescence amplification characteristics of the doped material Yb3+. Furthermore, theoretical analysis indicates the modes in YTMF at 1064nm, which is located in the amplified wavelength, can support nine modes carrying OAM. Therefore, the related experiments were performed and verified that the transmission modes can respectively carry 1, 2, and 3-order OAM at 1064nm in different coupling cases. These excellent properties indicate that the combination of doped materials and helical fiber provide favorable conditions for the generation and amplification of OAM, which provides a basis for the further development of OAM beams in the field of quantum communication and dense space division multiplexing.

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