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IEEE Conference on Telecommunications, Optics and Computer Science (TOCS)

Co-propagation of CV-QKD and classical signals over DWDM-based 5G fronthaul optical networks

Wenpeng Gao, Weiwen Kong, J.D. van der Tang, Yuheng Xie, Tianqi Dou, Zhenhua Li, Qi Zhao, Na Chen, Yuanchen Hao

Published May 7, 2024• 0 citations
Publisher

Abstract

This study investigate the integration of discrete modulated coherent state (DMCS) continuous variable quantum key distribution (CV-QKD) with wavelength division multiplexing (WDM) in 5G fronthaul optical networks. Firstly, an architecture of quantum-classical co-propagation in C-band DWDM-based 5G fornthaul network is constructed and the wavelength assignment scheme for classical/quantum channels is designed. By assigning the quantum channels in band of low Raman scattering coefficient and setting the quantum-classical channel space to be 200 GHz, the proposed scheme can effectively reduce the spontaneous Raman scattering (SpRS) and four-wave-mixing (FWM) noise. Then, the secret key rate (SKR) of DMCS protocol and the excess noise induced by SpRS are analyzed theoretically to furtherly character the co-propagation architecture. Lastly, numerical simulation is carried out to evaluate the impact of SpRS noise on the CV-QKD performance. The simulation results show that by employing the proposed wavelength assignment scheme, the co-propagation system can support positive SKR at a maximum distance of approximately 41 km for 8 classical channels use and 30 km for 16 classical channels use, respectively. Our work can provide a reference for practical deployment of quantum secured 5G fronthaul optical networks.

DOI
10.1117/12.3025653

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This study investigate the integration of discrete modulated coherent state (DMCS) continuous variable quantum key distribution (CV-QKD) with wavelength division multiplexing (WDM) in 5G fronthaul optical networks. Firstly, an architecture of quantum-classical co-propagation in C-band DWDM-based 5G fornthaul network is constructed and the wavelength assignment scheme for classical/quantum channels is designed. By assigning the quantum channels in band of low Raman scattering coefficient and setting the quantum-classical channel space to be 200 GHz, the proposed scheme can effectively reduce the spontaneous Raman scattering (SpRS) and four-wave-mixing (FWM) noise. Then, the secret key rate (SKR) of DMCS protocol and the excess noise induced by SpRS are analyzed theoretically to furtherly character the co-propagation architecture. Lastly, numerical simulation is carried out to evaluate the impact of SpRS noise on the CV-QKD performance. The simulation results show that by employing the proposed wavelength assignment scheme, the co-propagation system can support positive SKR at a maximum distance of approximately 41 km for 8 classical channels use and 30 km for 16 classical channels use, respectively. Our work can provide a reference for practical deployment of quantum secured 5G fronthaul optical networks.
We demonstrate experimentally the feasibility of continuous variable quantum key distribution (CV-QKD) in dense-wavelength-division multiplexing networks (DWDM), where QKD will typically have to coexist with several co-propagating (forward or backward) C-band classical channels whose launch power is around 0 dBm. We have conducted experimental tests of the coexistence of CV-QKD multiplexed with an intense classical channel, for different input powers and different DWDM wavelengths. Over a 25 km fiber, a CV-QKD operated over the 1530.12 nm channel can tolerate the noise arising from up to 11.5 dBm classical channel at 1550.12 nm in the forward direction (9.7 dBm in backward). A positive key rate (0.49 kbits s −1 ) can be obtained at 75 km with classical channel power of respectively −3 and −9 dBm in forward and backward. Based on these measurements, we have also simulated the excess noise and optimized channel allocation for the integration of CV-QKD in some access networks. We have, for example, shown that CV-QKD could coexist with five pairs of channels (with nominal input powers: 2 dBm forward and 1 dBm backward) over a 25 km WDM-PON network. The obtained results demonstrate the outstanding capacity of CV-QKD to coexist with classical signals of realistic intensity in optical networks.
A coherent transmission methodology for a continuous-variable quantum key distribution (CV-QKD) system based on quantum-heterodyne measurement through a coherent intradyne receiver is experimentally demonstrated in the framework of 5G mobile fronthaul links. Continuous optical carrier synchronization is obtained through training information, which is multiplexing to the quantum signal as pilot tone in both, frequency and polarization. Spectral tailoring by means of optical carrier suppression and single-sideband modulation is adopted to simultaneously mitigate crosstalk into the quantum channel and self-interference for the pilot tone, thus allowing for a high signal-to-noise ratio for this training signal. Frequency offset correction and optical phase estimation for the free-running local oscillator of the receiver is accurately performed and guarantees low-noise quantum signal reception at high symbol rates of 250 MHz and 500 MHz with additional Nyquist pulse shaping. A low excess noise in the order of 0.1% to 0.5% of shot-noise units is obtained for fiber-based transmission over a fronthaul link reach of 13.2 km. Moreover, co-existence with 11 carrier-grade classical signals is experimentally investigated. Joint signal transmission in the C-band of both, quantum signal and classical signals, is successfully demonstrated. Secure-key rates of 18 and 10 Mb/s are obtained under strict security assumptions, where Eve has control of the receiver noise, for a dark and a lit fiber link, respectively. Moreover, rates of 85 and 72 Mb/s are resulting for a trusted receiver scenario. These secure-key rates are well addressing the requirements for time-shared CV-QKD system in densified 5G radio access networks with cloud-based processing.
Integrating quantum key distribution (QKD) on the existing optical fiber network through dense wavelength-division multiplexing (DWDM) can greatly reduce the costs of quantum channels and improve the scalability and flexibility of the quantum communication network. In the scenarios of an access network or local area network with a large number of users, the connected optical fibers are relatively short and the quantum signal can be adjacent to the classical channels. In this case, the four-wave-mixing noise generated by the classical lights will have a severe impact on the performance of the QKD. We establish a theoretical model to characterize the excess noise in continuous-variable QKD induced by the four-wave mixing, and experimentally demonstrate the validity of the theoretical predictions. In addition, the influence of cross-phase-modulation noise between the carrier of the quantum signal and classical data channels on the QKD is investigated. To suppress the effect of the four-wave-mixing noise, an unequal channel spacing technique is employed. We realize coexistence of entangled state-based continuous-variable QKD and five adjacent DWDM classical channels with 10 dBm launch power and nonreturn-to-zero on-off-keying modulation at 2.5 Gb/s (10 Gb/s).
In this paper, the crosstalk-induced impact of coexisting dense-wavelength-division-multiplexed (DWDM) channels on continuous-variable quantum key distribution (CV-QKD) in practical communication environment is investigated. We analyze the nonlinear effect resulting from classical channels on the transmitted local oscillator in CV-QKD, while various existing studies mainly focus on the crosstalk-induced excess noise. We demonstrate that the generally ignored phenomenon of four-wave mixing in excess noise analysis is a visible factor causing local oscillator fluctuation characterized by the statistical properties of the power evolution of local oscillator. Besides, the impact of stimulated Raman scattering on local oscillator is derived in the same theoretical approach and experimentally investigated. Finally, by establishing a trusted model for local oscillator fluctuation we perform the security analysis to constrain the threshold of fluctuation. All of the above analysis should be taken into account as a supplementary for evaluating the performance of CV-QKD with coexisting DWDM system and optimal allocation of classical and quantum channels.
In this letter, we report on the advances toward the integration of our developed continuous variables (CV) quantum key distribution (QKD) system in existing optical infrastructure and wavelength division multiplexed (WDM) networks. First, we investigate the tolerance of the CV-QKD system to spontaneous Raman scattering (SRS) noise, the latter being the most dominant impairment in a WDM co-existence environment for QKD. In particular, we investigate by experiment the impact of a WDM10×1010\times 1010×10Gb/s ON–OFF-keying signal in terms of induced SRS noise in the QKD channel. The spontaneous SRS noise influence is assessed for different transmission scenarios, i.e., for various optical launch powers of the WDM signal, and for different transmission links of 20, 40, 60, and 80 km. Based on the experimental data and on the measured system’s parameters, we estimate the key rates and reach capabilities of the proposed CV-QKD system. The scheme supports a key rate of 90 kbit/s over 20 km, for an ideal QKD system multiplexed with 2-mW optical power. A step further, we demonstrate for first time the use of the aforementioned CV-QKD system to encrypt a 10GE client service over deployable optical transport network legacy equipment over 20 km. Our results prove the feasibility of the integration of our proposed scheme with legacy telecom equipment in existing WDM optical networks.
5G is another age of broadband portable correspondence innovation including high speed, low latency, and large connectivity, and quantum cryptography is a technology of the combination of quantum mechanics and cryptography. In order to combine 5G fronthual with the QKD (quantum key distribution), we conduct research on this paper. First, this paper proposes DWDM-QKD (dense wavelength division multiplexing-quantum key distribution) 5G fronthaul architecture. It contains AAU (active antenna unit) sites, multiplexer, de-multiplexer, and DU (distributed unit) sites. Second, the spontaneous Raman scattering noise interference model is analyzed theoretically, and the secure key rate calculation theory is used. Finally, the simulation evaluates the performance of QKD in the proposed architecture, the reduction of classical power can lead to an increase in the secure key rate.