Large mode area (LMA) fibers are widely used in high power fiber lasers to solve the nonlinear problems. In this work, a Nd 3+ -doped phosphate glass LMA fiber with heterogeneous helical claddings (HHC) is fabricated successfully by rod in tube method for the first time. The performance of the preform glass was matched well and suitable for drawing the fiber, and the related fabrication method is helpful for other special structure fiber fabrication. The fiber performance such as loss and gain coefficients are both tested and compared respectively. The experiment results show that the loss coefficient α will increase with the decrease of Λ (helix pitch) or r (fiber core radius), furtherly, the net gain coefficient g will become larger with the increase of r or Λ. The experiment results are beneficial to the HHC fiber design furtherly. As the HHC fiber has an all-solid-state structure, it is easy to fabricate relatively and convenient for cutting, splicing, etc. Thus, the HHC fiber will have potential applications in the field of fiber lasers.

Large mode area (LMA) fibers are widely used in high-power fiber lasers to solve the nonlinear problems. In this Letter, a novel LMA fiber with heterogeneous helical claddings (HHCs) is proposed. A coordinate transformation simulation technique is adopted to analyze the fiber mode transmission characteristics. The effects of the fiber parameters such as θ , Λ , r , n 0 , n 1 , n 2 , n 3 , and λ on the mode transmission characteristics include loss coefficient L and effective mode area A e f f . When θ = 14 ∘ , Λ = 22 m m , n 0 = n 2 = 1.439 , and n 1 = n 3 = 1.438 are adopted. The loss coefficients are L 01 = 0.093 d B / m , L 11 = 9.47 d B / m , and L 21 = 23.36 d B / m ; the single-mode fiber diameter 2 r is at least 60 µm; and the corresponding effective mode field area A e f f is 2025 µ m 2 . As the helix pitch is a centimeter order of magnitude and the fiber is all solid state, the HHC fiber is relatively easy to fabricate and convenient for cutting, splicing, etc., and will be well applied in the field of high-power fiber lasers.

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