Nowadays, helically phased light carrying orbital angular momentum (OAM) is well known, as exciting progress on the applications of OAM modes has been made in various fields. OAM modes, as a complete set of orthogonal basis functions for spatial distribution of electromagnetic field with theoretically infinite topological states, have attracted widespread interest in the field of optical fiber-based communications.
Over the past few years, researchers have been applying OAM MDM technology into fiber-based optical communication systems, in which ring fiber was introduced for supporting numerous OAM modes to significantly reduce the modal crosstalk. In order to further improve the transmission speed of information in the fiber-based communication system, the combination of OAM MDM and wavelength division multiplexing (WDM) technologies would be necessary. As when the OAM-based communication system is proposed, WDM technology and its corresponding devices have been pretty mature and widely implemented. Thus, more improvements are required for fibers supporting OAM modes to suit the needs in WDM systems.
Chromatic dispersion, as one of the key parameters to impact the quality of the transmitted optical signal over wide bandwidth, is the first thing to be considered. Although the influence of chromatic dispersion can be handled by digital signal processing (DSP), the corresponding power consumption will increase with the chromatic dispersion for correction. Recently, coupled ring fiber design has also been proposed to realize large negative dispersion, which could potentially be used as a dispersion compensating element for OAM mode. But still a laudable goal would be to further simply the optical link for easier fiber management and more practical system implementation. Thus comes the demand for designing the non-zero dispersion-shifted fiber (NZDSF) for supporting OAM modes to balance the chromatic dispersion and nonlinearity.
In this talk, we will first introduce the basic concept for apply the OAM modes into optical communication, the main driving force for introducing the NZDSF for OAM mode, and its applications in the fiber-based communication systems. As the ring-shaped fiber has gain encouraging improvement in supporting numerous OAM modes, and the NZDSF is building on that, the previous researches for optical ring-fiber carrying OAM modes will be also discussed.
We will then discuss the novel designed NZDSF for OAM modes. The ordinary ring-shaped fiber design with low chromatic dispersion for HE2,1 mode, which can serve as NZDSF for its corresponding OAM1,1 mode, is achieved by adjusting the fiber structure and materials. The theoretical analysis shows that a negative dispersion of -1.246 ps/(nm•km) or a positive dispersion of 1.541 ps/(nm•km) can be obtained at wavelength of 1550 nm, with the dispersion variation of less than 4 ps/(nm•km) for OAM1,1 mode from 1530 to 1625 nm, covering the entire C-band and L-band.