Abstract
The radially anisotropic ring-core fiber with cylindrical birefringence is theoretically and numerically investigated as a novel platform for the transmission of vector-vortex beams with unique modal properties. First, we elucidate the parametric conditions where such fiber enables modal substitution in which either the donut-shaped azimuthal TE01 or radial TM01 mode replaces the normal Gaussian-like HE11 mode as the fundamental mode of the waveguide. We also demonstrate that it is possible to significantly engineer the waveguiding properties of the fiber via the addition of small radial birefringence (∼10−4) so as to make the (hitherto non-degenerate) TE0m and TM0m modes fully degenerate. The latter property is used to create stable vortex modes of high purity (>99%) with the newly degenerate modal pair – a feat not possible with standard few-mode fibers—all without affecting the co-propagating hybrid HE/EH modes that remain available as an independent basis set to produce vortex beams of similarly high purity. These new insights are relevant to the topical fields of mode-division multiplexing (MDM), structured light, fiber modelling and fabrication. With respect to MDM applications, the newly available vortex modes created with the degenerate TE/TM basis set can now be concurrently used with the more common vortex modes created via the HE/EH modal basis set.
Highlights
Anisotropic fibers are a special class of optical fibers, first studied by Black et al, where the fiber displays cylindrical birefringence [1]
Ring-core fibers have shown to be a favorable structure for high-order mode guiding in radially anisotropic fibers [1,5], but was more recently actively studied for the stable transmission of vector as well as vortex beams (that carry orbital angular momentum (OAM)) owing to their ability to lift the near modal degeneracy between adjacent eigenmodes [6]
We investigated the modal properties of the first two mode families (LP01 and LP11) in the proposed radially anisotropic ring-core fibers for a range of absolute core refractive indices, 1.45 ≤ nrco ≤ 1.50 and 1.45 ≤ nφco ≤ 1.50, which translate into the following range of normalized refractive index contrasts: 0.42 ×10−2 ≤ ∆r ≤ 3.9 ×10−2 and 0.42 ×10−2≤ ∆φ ≤ 3.9 ×10−2
Summary
Anisotropic fibers are a special class of optical fibers, first studied by Black et al, where the fiber displays cylindrical birefringence [1] Their theoretical analysis distinctively showed that a radially anisotropic optical fiber could be designed such as to have the fundamental mode to be either the azimuthal TE01 or radial TM01 mode instead of the usual linearly polarized HE11 mode [1]. Such fiber exhibits polar anisotropy, aka cylindrical material birefringence, where either the fiber core or cladding demonstrates different material refractive indices along the radial and azimuthal directions in polar coordinates [1,2,3,4]. Radially anisotropic fibers with a ring-core structure offer a promising platform for studying structured light beams, which lends to further investigation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
