Generation of the First-Order OAM Modes in Single-Ring Fibers by Offset Splicing Technology

A method of generating the first-order orbital angular momentum (OAM) modes in a single-ring fiber is proposed and demonstrated through an all-fiber structure. The first-order OAM modes (L = ±1) refer to a combination of HE
₂₁
^even
mode and HE
₂₁
^odd
mode. According to the donut-like shape distribution of the HE
₂₁
mode, a standard single-mode fiber can be utilized to excite the HE
₂₁
mode in the ring fiber by a lateral-offset splicing. By adjusting the polarization of these two modes, the two first-order OAM modes can be excited separately. Based on this simple structure, the OAM modes can be generated in a broadband wavelength ranging from 1540 to 1580 nm. Moreover, the stable transmission of the generated OAM modes in a 7 m long such ring fiber has been demonstrated.