Generation of radial higher-order orbital angular momentum mode in helically-twisted elliptic fiber

The generation mechanism and regulation method of the radial higher-order orbital angular momentum (OAM) mode based on helically twisted elliptic fiber (HTEF) are investigated. This work aims to reveal the quantitative relation between the twisted rate ( α ) and the target radial higher-order OAM mode. From theoretical simulations, it is concluded that α is the key to regulating the radial higher-order OAM mode. In the experiment, OAM 2 n modes with radial higher-order n of 2, 3, 4, and 5 are successfully generated at 1550 nm by regulating α of the HTEF. Finally, the transmission spectrum and purity measurements are performed for the OAM 24 mode, and it can be concluded that the fabricated experimental samples have more than 90% conversion efficiency and close to 94% purity under the appropriate α and twisted length.