Abstract
Abstract Light carrying orbital angular momentum constitutes an important resource for both classical and quantum information technologies. Its inherently unbounded nature can be exploited to generate high-dimensional quantum states or for channel multiplexing in classical and quantum communication in order to significantly boost the data capacity and the secret key rate, respectively. While the big potentials of light owning orbital angular momentum have been widely ascertained, its technological deployment is still limited by the difficulties deriving from the fabrication of integrated and scalable photonic devices able to generate and manipulate it. Here, we present a photonic integrated chip able to excite orbital angular momentum modes in an 800 m long ring-core fiber, allowing us to perform parallel quantum key distribution using two and three different modes simultaneously. The experiment sets the first steps towards quantum orbital angular momentum division multiplexing enabled by a compact and light-weight silicon chip, and further pushes the development of integrated scalable devices supporting orbital angular momentum modes.
Highlights
Optical beams possessing a well-defined orbital angular momentum (OAM) are characterized by the azimuthal phase dependence eilφ, where lħ is the OAM carried by each photon, with ħ being the reduced Planck constant; l is the topological charge, an integer that specifies the OAM value, and φ is the azimuthal angle
We have successfully demonstrated the simultaneous transmission of three different quantum key distribution (QKD) signals multiplexed using OAM fiber modes excited by an integrated photonic chip
Due to the low sensitivity of thermo-optics modules, in our experiment the mode crosstalk increased with the number of active modes, increasing the overall quantum bit error rate (QBER) and lowering the final secret key rate achievable in the 3-mode test in comparison with 2-mode one
Summary
Optical beams possessing a well-defined OAM are characterized by the azimuthal phase dependence eilφ, where lħ is the OAM carried by each photon, with ħ being the reduced Planck constant; l is the topological charge, an integer that specifies the OAM value, and φ is the azimuthal angle. OAM has been largely investigated in the field of fiber-based optical communication, both classical and quantum, achieving unprecedented results that have forecast its exploitation to real-case scenarios [7–9] It has shown great potentials in communication systems due to the unbounded nature of the topological charge l and the inherent orthogonality between optical modes or quantum states. These characteristics are exceptional resources for optical mode multiplexing and high-dimensional quantum communication: the former aims to overcome the channel capacity crunch in classical communication systems [10, 11] or to boost photon information efficiency in the quantum ones [8]; the latter, uses quantum states encoded in a large Hilbert space, i.e., high-dimensional quantum states, as
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