12 Mode, MIMO-Free OAM Transmission

Abstract

Simultaneous MIMO-free transmission of a record number (12) of orbital angular momentum modes over 1.2 km is demonstrated. WDM compatibility of the system is shown by using 60 WDM channels with 25 GHz spacing and 10 GBaud QPSK. IntroductionOrbital angular momentum (OAM) carrying modes of optical fibers have received significant attention recently for their potential use in mode division multiplexing (MDM) as independent data carriers without the use of cost and power intensive multiple-input-multiple-output (MIMO) digital signal processing. OAM modes are characterized by a helical phase profile, ‫,‪߮ሻ‬ܮ݅‪ሺ‬ݔ݁‬ where ߮ is the azimuthal coordinate and ‫ܮ‬ is the topological charge, and a circular polarization ߪ േ ൌ ‫ݔ‬ ො േ ‫ݕ݅‬ ො. They come in pairs with OAM and circular polarization of the same handedness (spinorbit aligned) or different handedness (spin-orbit anti-aligned). With appropriate fiber design, such modes are separated from their nearest neighbors in effective index (n eff ), and have been shown to be propagation-stable on the order of kilometers [1].Previously, MIMO-free data transmission has been demonstrated with four OAM modes over km-lengths of suitably designed optical fibers [2,3]. Although fibers supporting a larger number of OAM states have been designed and tested [4,5], data transmission over a larger ensemble of OAM modes remains to be demonstrated.This work investigates MDM transmission using 10 GBd QPSK of 12 OAM modes, i.e. the largest number of mode groups transmitted MIMO-free, over 1.2 km. It is found that all the data channels are below the soft-decision forward error correction (SD-FEC) limit using a 25GHz-spaced frequency comb producing 60 WDM channels.

12 mode, WDM, MIMO-free orbital angular momentum transmission

“…This work investigates MIMO-free MDM transmission of 12 OAM modes, and is an extension of our previous report [12]. This is the highest number of modes transmitted MIMO-free over a fiber longer than 1 km.…”

Scalable mode division multiplexed transmission over a 10-km ring-core fiber using high-order orbital angular momentum modes

“…MIMO-free approaches mainly include mode-group multiplexing [6,7] and orbital angular momentum (OAM) mode multiplexing [8][9][10][11]. They aim to suppress crosstalk among all channels with large differential effective refractive indices (Δneff) between modes or mode groups (MGs).…”

“…To suppress modal XT over km-scale propagation, Δn eff > 1x10 −4 is typically required [9], and this requirement should become more critical when the distance is further increased. The most successful demonstrations of OAM-MDM based MIMO-free data transmission so far are realized over the distances of 1-2 km [9][10][11]. Recently, an air core fiber that supports good quality OAM mode transmission has been demonstrated, in which the intra-MG Δn eff of up to 1.7x10 −4 is achieved [14].…”

SLM phase mask optimization for fiber OAM mode excitation

“…The scientific research dedicated to mode-division multiplexing has recently led to the exploitation of the orthogonality of fiber OAM modes. [1][2][3][4] These modes can be excited by illuminating one fiber end with a properly tailored light beam. One method to create such a beam is by means of a phase-only SLM.…”