Experimental demonstration of broadband generation of optical vortices using asymmetrically spliced fibers

Optical vortex (OV) beams have received considerable interest in the recent years. For miscellaneous OV-based applications, one important issue is the generation of OV beams. A lot of approaches including both external and intra-cavity methods have been demonstrated. Meanwhile, using fibers for generating OV beams has also attracted more and more attention because of the inherent advantages of fibers, such as compactness, low cost, remote delivery and flexibility. Although, successful generation of OV beams with optical fibers has been demonstrated, one may also see several challenges, like narrow bandwidth, complex structures, and high insertion loss. In this paper, we propose and experimentally demonstrate a simple approach to realize controllable broadband OV generator using optical fibers. The generator consists of a single-mode fiber (SMF) of which the output end is spliced to a two-mode fiber (TMF) with a defined offset, two polarization controllers (PCs) applied on the SMF and TMF, and one polarizer. The polarizer located behind the output end of the TMF is used to filter the non-OV beams. By adjusting the two PCs, one can selectively convert an input fundamental mode to high-purity OV modes within a wide bandwidth (1480 nm ∼1640 nm). The measured extinction ratio of generated OV modes is larger than 20 dB. The proposed simple low-cost broadband fiber-based OV generator may have wide applications in the area such as fiber communications, sensing and imaging.