Orbital angular momentum modes in twisted anti-resonant fiber with dielectrically chiral tube cores.

Abstract We propose and investigate a twisted dielectrically chiral anti-resonant
fiber (TCARF) by introducing chiral media into the inner core of six cladding tubes
to generate orbital angular momentum (OAM). The numerical results show that the
combined effects of structural chirality (twisting) and dielectric chirality lift the mode
degeneracy within the same mode order both in the core and tube. Consequently, the
effective refractive indices of the core modes and tube modes experience a refractive
index splitting. Besides, the mode couplings between the core modes and tube modes
were also tuned by the dielectric chirality parameter and twist rate. Additionally, the
combined effects of twist rate and dielectric chirality result in differential confinement
loss between the same modes belonging to the same mode group and a shift in the
confinement loss peaks of OAM modes with opposite handedness. This differential
loss between OAM modes with opposite handedness results in polarization filtering.
The working wavelength of the filter ranges from 1.5 µm to 1.6 µm by varying the
chirality parameter. The ARF we proposed in this paper can selectively filter out the
polarized light in one direction by adjusting the chirality parameter in the tube core.