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arXiv:1905.05932

Multicore fiber-based quantum access network

Chun Cai, Yongmei Sun, Jianing Niu, Peng Zhang, Yongrui Zhang, Yuefeng Ji

Published May 15, 2019• 1 citation
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Abstract

We propose a quantum access network based on multicore fiber (MCF) to scale up the number of users in quantum key distribution (QKD) networks. The MCF is used as feeder fiber and single core single mode fibers (SSMFs) are used as drop fibers. Quantum signals (QSs) are integrated with classical signals (CSs) in both MCF and SSMFs to save deployment cost since access networks are cost sensitive. Due to the integration, spontaneous Raman scattering (SRS) and intercore crosstalk (ICXT) are the main impairment sources to QKD. To alleviate the noise, we propose a core and wavelength assignment scheme (CWAS) that a dedicated core of MCF is used to transmit QSs and the wavelengths of QSs are set lower than those of upstream signals. Also, we demonstrate that wavelength time division multiplexing (WTDM) is suitable for QSs which are required to support large number of quantum users, since WTDM can realize higher secure key rate (SKR) than time division multiplexing (TDM) and require lower cost than wavelength division multiplexing (WDM). Finally, the proposed quantum access network is verified experimentally. The experiment results are consistent with our analysis. The properties of SRS in the proposed architecture are shown in the experiments through the quantum bit error rates (QBERs) in different experimental case, which verifies the superiority of the proposed CWAS. Also, the characteristics of the SKRs prove that the number of receivers has a great impact on the performance of QSs using WTDM.

DOI
10.48550/arxiv.1905.05932

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We propose a quantum access network based on multicore fiber (MCF) to scale up the number of users in quantum key distribution (QKD) networks. The MCF is used as feeder fiber and single core single mode fibers (SSMFs) are used as drop fibers. Quantum signals (QSs) are integrated with classical signals (CSs) in both MCF and SSMFs to save deployment cost since access networks are cost sensitive. Due to the integration, spontaneous Raman scattering (SRS) and intercore crosstalk (ICXT) are the main impairment sources to QKD. To alleviate the noise, we propose a core and wavelength assignment scheme (CWAS) that a dedicated core of MCF is used to transmit QSs and the wavelengths of QSs are set lower than those of upstream signals. Also, we demonstrate that wavelength time division multiplexing (WTDM) is suitable for QSs which are required to support large number of quantum users, since WTDM can realize higher secure key rate (SKR) than time division multiplexing (TDM) and require lower cost than wavelength division multiplexing (WDM). Finally, the proposed quantum access network is verified experimentally. The experiment results are consistent with our analysis. The properties of SRS in the proposed architecture are shown in the experiments through the quantum bit error rates (QBERs) in different experimental case, which verifies the superiority of the proposed CWAS. Also, the characteristics of the SKRs prove that the number of receivers has a great impact on the performance of QSs using WTDM.
We propose a quantum-classical access network architecture based on multicore fiber to scale up the number of quantum key distribution (QKD) users. Quantum signals are integrated with classical signals in both feeder and drop fibers to save deployment cost since access networks are cost-sensitive. To increase the secure key rate (SKR) of QKD, we show that wavelength-time division multiplexing is suitable for quantum signals, which are required to support a large number of quantum users. Also, we propose a core and wavelength assignment scheme to alleviate spontaneous Raman scattering and intercore cross talk noise, which are the main impairment sources to QKD in this quantum-classical network. Finally, we experimentally show the performance of QKD in the proposed quantum-classical access network in terms of noise and channel loss. The experiment results are consistent with our analysis. The characteristics of the SKRs prove the superiority of wavelength-time division multiplexing. The properties of spontaneous Raman scattering in the feeder and drop fibers are shown in the experiments through the quantum bit error rates in different experimental conditions, which verifies the effectiveness of the proposed core and wavelength assignment scheme.
Broadband access in optical domain usually focuses in providing a pervasive cost-effective high bitrate communication in a given area. Nowadays, it is of utmost interest also to be able to provide a secure communication to the costumers in the area. Wireless access networks rely on optical domain for both fronthaul and backhaul of the radio access network (C-RAN). Multicore fiber (MCF) has been proposed as a promising candidate for the optical media of choice in nextgeneration wireless. The capacity demand of next-generation 5G networks makes interesting the use of high-capacity optical solutions as space-division multiplexing of different signals over MCF media. This work addresses secure MCF communication supporting C-RAN architectures. The paper proposes the use of one core in the MCF to transport securely an optical quantum key encoding altogether with end-to-end wireless signal transmitted in the remaining cores in radio-over-fiber (RoF). The RoF wireless signals are suitable for radio access fronthaul and backhaul. The theoretical principle and simulation analysis of quantum key distribution (QKD) are presented in this paper. The potential impact of optical RoF transmission crosstalk impairments is assessed experimentally considering different cellular signals on the remaining optical cores in the MCF. The experimental results report fronthaul performance over a four-core optical fiber with RoF transmission of full-standard CDMA signals providing 3.5G services in one core, HSPA+ signals providing 3.9G services in the second core and 3GPP LTEAdvanced signals providing 4G services in the third core, considering that the QKD signal is allocated in the fourth core.
To ensure the security of optical networks in the future, integrating quantum key distribution (QKD) with optical networks is one of the solutions. Moreover, the optical network based on multi-core fiber (MCF) is also one of the ways to improve the transmission capacity. Therefore, we study the integration of QKD into MCF-enabled optical networks. Aiming at the resource allocation problem of MCF-enabled wavelength division multiplexing optical networks, this paper proposes a resource allocation scheme which is suitable for independent-core-transmission of classical signals and quantum signals. For core resource, we propose the alternate core allocation algorithm. For wavelength resource, we propose the iteration-based wavelength allocation algorithm. The overall scheme uses the proposed two algorithms to first allocate the core and then allocate the wavelength. The simulation results show that the proposed scheme has a great improvement in secret key rate (SKR) compared with the benchmark scheme on the regular hexagonal 7-core fiber and 19-core fiber. And the proposed scheme still has good performance under long transmission distance and high classical signal power.
The quantum-classical coexistence can be obtained using wavelength division multiplexing (WDM), however, the crosstalk between quantum and classical signals due to Raman noise must be handled with extra attention. Multi-core fiber (MCF) provides a good solution for the coexistence based on space division multiplexing (SDM). In this work, we propose and experimentally demonstrate hybrid transmission of ultrastable optical frequency reference and quantum key distribution (QKD) over homogeneous MCF. The scheme achieves optical frequency stabilization at the remote site by beating the loopback frequency signal with a local reference to extract link phase noise, which is then compensated via voltage-controlled oscillator (VCO) feedback. Prior to the experiment, we first analyze the critical challenges in MCFs including inter-core crosstalk and inter-core spontaneous Raman scattering. To minimize the crosstalk between the signals, the quantum signal and the optical frequency propagate through separate fiber cores. Successful hybrid transmission of optical frequency references and QKD is achieved across 20 km seven-core fiber. The frequency instability of1.2×10−171.2 \times 10^{-17}1.2×10−17at 1 s and4.2×10−194.2 \times 10^{-19}4.2×10−19at 10000 s, and secure key rate of 317.28 kbps can be realized in this integrated transmission system. The scheme benefits from two merits, ultrastable optical frequency offers high-precision clocks to QKD, and QKD provides one-time-pad keys to encrypt the time data. These results demonstrate the feasibility and tolerance of our QKD system with high-precision frequency reference and the viability of multi-core fibers for next-generation quantum networks.
Multicore-fibres (MCF) have emerged as an attractive solution for capacity scaling in optical communication. Securing such links with Quantum Key Distribution (QKD) is critical with the advent of Quantum computers. For practical deployment, QKD is required to operate alongside high-speed classical communication over field-deployed fiber infrastructure. In this work, the performance of QKD is experimentally evaluated in coexistence with high-speed classical data transmission over field-deployed underground and aerial multicore fiber links. The QKD system is implemented with Coherent One-Way Slim protocol, with dedicated Quantum and classical channels for Quantum communication and QKD post-processing. The deployed 4-core MCF infrastructure at IIT Madras provides an effective transmission length of 48 km through loopback operation. QKD performance over the MCF is evaluated in terms of quantum bit error rate (QBER) under varying attenuation, controlled noise injection, and inter-core crosstalk over both singlecore fiber and MCF links. The experimental results show that inter-core crosstalk has a stronger impact in MCF, leading to increased excess noise at the quantum receiver. For a 32-GBaud PM 16-QAM classical modulation format, stable QKD operation is maintained when the spectral separation is approximately six to eight times the occupied bandwidth.
We demonstrate quantum key distribution (QKD) with classical signals in a seven-core fiber using dense wavelength division multiplexing. Quantum signals are transmitted in an outer core separately and intercore crosstalk (IC-XT) is the main impairment of them. In order to alleviate IC-XT, we propose a quantum-classical interleave scheme. Then the properties of IC-XT are analyzed based on the measurement results, which indicate counter-propagation is a better co-existence method than co-propagation. Finally, we perform QKD experiments in the presence of two classical channels with a channel spacing of 100 GHz between quantum channel and the nearest classical channels. The experiment results prove counter-propagation almost immune to IC-XT, which is consistent with our analysis. Also, the feasibility of the transmission over the range of metropolitan area networks is validated with our scheme.