Generation of optical vortices in spun multihelicoidal optical fibers

Abstract

We have theoretically studied long-period spun l-helicoidal fibers and their ability to generate singular beams from regular ones. On the basis of perturbation theory in the presence of degeneracy, applied to the scalar waveguide equation, we obtained the structure of coupled modes of such fibers and their spectra. It is shown that the coupled modes consist of the fields, which taken separately bear topological charges that differ by l units. We have numerically studied the process of the passage of a Gaussian beam through such a fiber and demonstrated that long-period l-helicoidal fibers have the ability to change-in a certain wavelength range-the topological charge of the incoming Gaussian beam by l units, generating in this way charge-l optical vortex.

Conversion of orbital angular momentum of light in chiral fiber gratings

“…As seen from Table 3, OAM beams with the charge 1 and 3 can be generated in L-1-CFGs, while those with not only charge N revealed in [6], but also charge N 2 can be generated in L-N-CFGs (N ≥ 2). Specifically, OAM beams with the charge 2 and 4 can be generated in L-2-CFGs, which will be used for converter design later.…”

“…It was demonstrated that long-period l-helicoidal fibers can generate an OAM beam with charge l [6]. The aim in this Letter is to demonstrate all the charged OAM beams possibly generated in chiral fiber gratings (CFGs) with multiple-fold rotation symmetry in the cross section.…”

“…Much effort has been devoted, and fiber-based compact and efficient technology has become a promising class among the present methods. Proposed schemes include using multimode fibers [4], weakly and highly twisted and spun fibers [5,6], helically twisted photonic crystal fibers [7], and special ring fiber structures [8].It was demonstrated that long-period l-helicoidal fibers can generate an OAM beam with charge l [6]. The aim in this Letter is to demonstrate all the charged OAM beams possibly generated in chiral fiber gratings (CFGs) with multiple-fold rotation symmetry in the cross section.…”

“…The cross section may have theoretically arbitrary-fold rotation symmetry originating from geometry-or stress-induced perturbation [10]. The longitudinal variation is similar to that of spun fibers discussed in a set of enlightening works by Alexeyev and co-workers [5,6]. Here we call the spun fiber with N-fold rotation symmetry in the cross section N-CFG to highlight its three salient properties in regard to the generation and conversion of OAM beam, as well as the interactions of OAM and SAM to be discussed below.…”

“…Much effort has been devoted, and fiber-based compact and efficient technology has become a promising class among the present methods. Proposed schemes include using multimode fibers [4], weakly and highly twisted and spun fibers [5,6], helically twisted photonic crystal fibers [7], and special ring fiber structures [8].…”