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Quantum networks are the ultimate target in quantum communication, where many connected users can share information carried by quantum systems. The keystones of such structures are the reliable generation, transmission and manipulation of quantum states. Two-dimensional quantum states, qubits, are steadily adopted as information units. However, high-dimensional quantum states, qudits, constitute a richer resource for future quantum networks, exceeding the limitations imposed by the ubiquitous qubits. The generation and manipulation of such D-level systems have been improved over the last ten years, but their reliable transmission between remote locations remains the main challenge. Here, we show how a recent air-core fiber supporting orbital angular momentum (OAM) modes can be exploited to faithfully transmit D-dimensional states. Four OAM quantum states and their superpositions are created, propagated in a 1.2 km long fiber and detected with high fidelities. In addition, three quantum key distribution (QKD) protocols are implemented as concrete applications to assert the practicality of our results. This experiment enhances the distribution of high-dimensional quantum states, attesting the orbital angular momentum as vessel for the future quantum network.

Simultaneous MIMO-free transmission of 12 orbital angular momentum (OAM) modes over a 1.2 km air-core fiber is demonstrated. WDM compatibility of the system is shown by using 60, 25 GHz spaced WDM channels with 10 GBaud QPSK signals. System performance is evaluated by measuring bit error rates, which are found to be below the soft FEC limit, and limited by inter-modal crosstalk. The crosstalk in the system is analyzed, and it is concluded that it can be significantly reduced with an improved multiplexer and de-multiplexer.

 Users may download and print one copy of any publication from the public portal for the purpose of private study or research.  You may not further distribute the material or use it for any profit-making activity or commercial gain  You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

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.