Charles Brunet

Design, fabrication and validation of an OAM fiber supporting 36 states

We present an optical fiber supporting 36 information bearing orbital angular momentum (OAM) states spanning 9 OAM orders. We introduce design techniques to maximize the number of OAM modes supported in the fiber; while avoiding LP mode excitation. We fabricate such a fiber with an air core and an annular index profile using the MCVD process. We introduce a new technique for shaping OAM beams in free-space to obtain better coupling efficiency with fiber with annular index profiles. We excite 9 orders of OAM in the fiber, using interferometry to verify the OAM state on exiting the fiber. Using polarization multiplexing and both signs for the topological charge, we confirm support of 36 states, exploiting to our knowledge the highest number of OAM modes ever transmitted in optical fiber.

Design of a family of ring-core fibers for OAM transmission studies

We propose a family of ring-core fibers, designed for the transmission of OAM modes, that can be fabricated by drawing five different fibers from a single preform. This novel technique allows us to experimentally sweep design parameters and speed up the fiber design optimization process. Such a family of fibers could be used to examine system performance, but also facilitate understanding of parameter impact in the transition from design to fabrication. We present design parameters characterizing our fiber, and enumerate criteria to be satisfied. We determine targeted fiber dimensions and explain our strategy for examining a design family rather than a single fiber design. We simulate modal properties of the designed fibers, and compare the results with measurements performed on fabricated fibers.

Vector Mode Analysis of Ring-Core Fibers: Design Tools for Spatial Division Multiplexing

Design tools have existed for decades for standard step-index fibers, with analytical expressions for cutoff conditions as a function of core size, refractive indexes, and wavelength. We present analytical expressions for cutoff conditions for fibers with a ring-shaped propagation region. We validate our analytical expressions against numerical solutions, as well as via asymptotic analysis yielding the existing solutions for standard step-index fiber. We demonstrate the utility of our solutions for optimizing fibers supporting specific eigenmode behaviors of interest for spatial division multiplexing. In particular, we address large mode separation for orbital angular momentum modes and fibers supporting only modes with a single intensity ring.

Mode division multiplexing using orbital angular momentum modes over 1.4 km ring core fiber

Mode division multiplexing (MDM) systems using orbital angular momentum (OAM) modes can recover the data in D different modes without recourse to full (2D × 2D) multiple input multiple output (MIMO) processing. One of the biggest challenges in OAM-MDM systems is the mode instability following fiber propagation. Previously, MIMO-free OAM-MDM data transmission with two modes over 1.1 km of vortex fiber was demonstrated, where optical polarization demultiplexing was employed in the setup. We demonstrate MDM data transmission using two OAM modes over 1.4 km of a specially designed ring core fiber without using full MIMO processing or optical polarization demultiplexing. We demonstrate reception with electrical polarization demultiplexing, i.e., minimal 2 × 2 MIMO, showing the compatibility of OAM-MDM with current polarization demultiplexing receivers.

Exciting OAM modes in annular-core fibers via perfect OAM beams

We generate perfect orbital angular momentum (OAM) beams with controllable ring width and ring diameter using a phase-only spatial light modulator. Perfect OAM beams facilitate coupling into annular and air-core fibers for spatial multiplexing of OAM modes.

Exact Expressions for Vector Mode Cutoff in Three-Layer Step-Index Fibers

Two-layer step-index fibers have well-known cutoff solutions, while cutoff solutions for three-layer step-index fiber exist for only one geometry (ring fiber). We derive exact expressions for cutoff frequencies of both vector and scalar modes for all geometries of three-layer step-index fibers. While vector modes have been solved for these fibers, to the best of our knowledge, this is the first time cutoff expressions are reported. Expressions for cutoff help predict the number of supported modes for a given fiber profile. Using these cutoff expressions, we deduce characteristics of fiber modal content as a function of fiber profile.

Design of a family of ring-core fiber for OAM

We present the design, simulation, and experimental characterization of a family of ring-core fibers suitable for OAM transmission. The simplicity of design and easily fabricated multiplicity of fibers facilitates analysis and modeling as compared to other OAM fibers.

Impact of MCMC convergence behavior on MMC parallelization

Multicanonical Monte Carlo (MMC) is a technique to accelerate simulations by using adaptive importance sampling (IS). Because the adaption algorithm is system independent, MMC is a practical, handy tool that can be used in many situations and in many fields of research. Combination of MMC with supercomputer infrastructures can support increasingly complex systems. A supercomputer works with parallelized algorithms. Efficient MMC relies on Markov Chain Monte Carlo (MCMC) as a key enabler in generating samples from biased distributions. While Monte Carlo simulations are embarrassingly parallelizable, MCMC is inherently serial in nature and a priori difficult to parallelize. In this article, we will examine three diverse systems to explore how MMC can benefit from parallelization. We will uncover some hints to parameterize the parallel algorithm to compromise between speed and accuracy.