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IEEE MetroCon

Toward Long-Haul Distribution of Multidimensional Spatially-Entangled Photons over Multicore Fibers

Amin Azaridoodaran, Mohammad Awwad, Cheng Guo, Michael Vasilyev

Published Nov 12, 2025• 1 citation
Publisher

Abstract

Spatial division multiplexing is a key technology for increasing the capacity of the classical optical fiber networks. It also provides additional degrees of freedom for photon entanglement and transmission in quantum communication networks. This paper describes steps toward generating a four-dimensional, spatially-entangled state and its distribution over multi-km-long four-core fibers. We generate four mutually coherent beams using a spatial light modulator and investigate their simultaneous coupling into a four-core fiber. We also verify the stability of both the relative phase and polarization between the cores over a 10 km of a four-core fiber.

DOI
10.1109/metrocon66796.2025.11405846

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Spatial division multiplexing is a key technology for increasing the capacity of the classical optical fiber networks. It also provides additional degrees of freedom for photon entanglement and transmission in quantum communication networks. This paper describes steps toward generating a four-dimensional, spatially-entangled state and its distribution over multi-km-long four-core fibers. We generate four mutually coherent beams using a spatial light modulator and investigate their simultaneous coupling into a four-core fiber. We also verify the stability of both the relative phase and polarization between the cores over a 10 km of a four-core fiber.
Spatial-division multiplexing is a key technology for increasing the capacity of classical optical fiber networks. It also provides additional degrees of freedom for photon entanglement and transmission in quantum communication networks. This paper describes steps toward generating a four-dimensional, spatially-entangled state and its distribution over multi-km-long four-core fibers. We generate four mutually coherent beams using a spatial light modulator and investigate their simultaneous coupling into a four-core fiber. We verify the stability of both the relative phase and polarization between the cores over10 km\mathbf{1 0 ~ k m}10 kmof a four-core fiber. We also characterize the polarization mode dispersion of the fiber and find its principal states of polarization to mitigate the effects of random polarization-dependent delay across the fiber cores.
The development and wide application of quantum technologies highly depend on the capacity of the communication channels distributing entanglement.Space-division multiplexing (SDM) enhances data channel transmission capacity in classical telecommunication and bears the potential to transfer the idea to quantum communication using current infrastructure.Here, we demonstrate a SDM of polarizationentangled photons over a 411 m long 19-core multicore fiber distributing polarization-entangled photon pairs through up to 12 channels simultaneously.The quality of the multiplexed transfer is evidenced by high polarization visibility and Clauser-Horne-Shimony-Holt (CHSH) Bell inequality violation for each pair of opposite cores.Our distribution scheme shows high stability over 24 h without any active polarization stabilization and can be effortlessly adapted to a higher number of channels.This technique increases the quantum-channel capacity and allows the reliable implementation of quantum networks of multiple users based on a single entangled photon pair source.
The development and wide application of quantum technologies highly depend on the capacity of the communication channels distributing entanglement. Space-division multiplexing (SDM) enhanced channel capacities in classical telecommunication and bears the potential to transfer the idea to quantum communication using current infrastructure. Here, we demonstrate an SDM of polarization-entangled photons over a 411m long 19-core multicore fiber distributing polarization-entangled photon pairs through up to 12 channels simultaneously. The quality of the multiplexed transfer is evidenced by high polarization visibility and CHSH Bell inequality violation for each pair of opposite cores. Our distribution scheme shows high stability over 24 hours without any active polarization stabilization and can be effortlessly adapted to a higher number of channels. This technique increases the quantum-channel capacity and allows the reliable implementation of quantum networks of multiple users based on a single entangled-photon pair source.
Quantum Key Distribution (QKD) is a crucial step in quantum cryptography protocols, as a secure distribution of the secret key is determinant in the performance of the system. Some QKD protocols like E91 require the distribution of entangled photon pairs between the emitter and the receiver in order to guarantee a safe transfer of information. However, the distribution of entangled quantum states is a remarkably challenging task, due to the fragility of this physical phenomenon. In this project, a new method for the distribution of high-dimensional entangled photon pairs through an optical fiber is presented. This method is based on the spatial modulation of the output beam of an Entangled Photon Source (EPS) in order to increase the coupling efficiency into a multi-core optical fiber (MCF), which otherwise is highly inefficient. In order to perform the spatial modulation, a LCoS phase-only Spatial Light Modulator (SLM) has been used. The presented method is designed for the modulation of a two-dimensional entangled photon beam, both entangled spatially and in polarization. So, the aim is not only to improve the overall single photon efficiency, but also the maximize as much as possible the coupling of entangled photon pairs, always maintaining the spatial correlations and the polarization entanglement. The system has been tested for a 810nmnmnm (NIR) central wavelength EPS, coupled into a 1m long MCF. The obtained results for the single photon efficiency are not as good as initially expected, due to limitations found in the setup along the course of the experiment. Nevertheless, the spatial correlation maintenance and the efficiency in the coupling of entangled photon pairs compared to the obtained single photon efficiency have resulted to be remarkable. The overall conclusion of this project is that the presented method has the potential to achieve much higher coupling efficiencies with some changes in the setup, always maintaining the entanglement. The versatility of the computed phase masks for the spatial modulation allows to adapt the shape of the beam to the used fiber, and also opens a door for other possible future applications. This applications can range from the implementation of the Hong-Ou-Mandel effect in optical fibers to the modulation of high-dimensional entangled photon pairs in other degrees of freedom, like frequency, OAM or time.
Fiber transport of multi-dimensional photonic qudits promises high information capacity per photon without space restriction. This work experimentally demonstrates transmission of spatial qudits through multi-core optical fibers and measurement of the entanglement between two fibers with quantum state analyzers, each composed of a spatial light modulator and a single-mode fiber. Quantum state tomography reconstructs the four-dimension entangled state that verifies the non-locality through concurrences in two-dimensional subspaces and a high-dimensional Bell-type CGLMP inequality.
Rapid recent advances in quantum technology are giving rise to potential new applications in a wide range of fields. In particular, efficient generation and distribution of quantum entanglement is crucial for many use cases in quantum communication. In this field, multi-core optical fibers (MCF) are especially interesting, as they enable space-division multiplexing, increasing data transmission capacity of the channel. In this work, we present a flexible system for efficient and scalable quantum communication through MCF, using phase-only spatial light modulation (SLM). Firstly, we utilise SLM to enhance the coupling efficiency of near-infrared polarization-entangled photon pairs into a 19-core MCF. Secondly, we present a novel SLM-based system which corrects random polarization transformations incurred over propagation through fiber, for all MCF cores in parallel. The quality of the distributed entanglement is certified by high polarization visibility and violation of the Clauser–Horne–Shimony–Holt (CHSH) inequality for every core pair. Our results show potential for implementation in real-world quantum communication networks, as well as enabling further advanced quantum experiments.