Abstract
We study theoretically the mode structure of few-mode helical core optical fibers with small (up to a wavelength order) values of the helix pitch. We demonstrate that in such fibers, at certain values of pitch the fundamental mode strongly hybridizes with optical vortices and the forbidden zone appears in the spectra of such hybrid modes, which results in their attenuation. We have shown that within the spectrum gap, the only forward-propagating guiding modes are represented by two circularly polarized optical vortices with opposite polarization and the same topological charge so that upon excitation of such a fiber with a circularly polarized beam, only a solitary optical vortex could be excited in it. Such “monovortex” fibers are found to be analogous to conventional monomode fibers that maintain the propagation of the mode.
- Received 16 April 2008
DOI:https://doi.org/10.1103/PhysRevA.78.013813
©2008 American Physical Society