Helical Bragg gratings filter for orbital angular momentum wave

Abstract

Effective filtration of orbital angular momentum (OAM) modes is essential to achieve multiple-channel data transmission in an OAM fiber for telecommunication applications. The nature of helical-shaped OAM wave propagation possessing many topological charges implies the need for uniquely designed index-modulated filters to conform to its twisted propagating direction in the fiber. Here, different from previous structures in demultiplexing OAM modes, a helical-shaped fiber grating structure concept is proposed as a pathway toward efficient demultiplexing of OAM modes in a fiber. A comparison of our proposed structure with the conventional fiber Bragg filter in transmitting an OAM wave shows a stronger reflection of the higher order OAM mode. We suggest that the proposed fiber Bragg structure has strong potential to be used for OAM fiber telecommunication technology.