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arXiv:1410.0656 · Journal of Lightwave Technology

Impact of Raman Scattered Noise from Multiple Telecom Channels on Fiber-Optic Quantum Key Distribution Systems

Thiago Ferreira da Silva, GUILHERME BARRETO XAVIER, Guilherme P. Temporão, Jean Pierre von der Weid

Published May 20, 2014• 81 citations
arXivHTMLPDF

Abstract

In this paper, we analyze the impact of the spontaneous Raman scattered noise generated from multiple optical classical channels on a single quantum key distribution channel, all within the telecom C-band. We experimentally measure the noise generated from up to 14 continuous-wave laser sources with different wavelengths using the dense wavelength division multiplexing (DWDM) standard, in both propagation directions in respect to the QKD channel, over different standard SMF-28 fiber lengths. We then simulate the expected secure key generation rate for a decoy-states-based system as a function of distance under the presence of simultaneous telecom traffic with different modulation techniques, and show a severe penalty growing with the number of classical channels present. Our results show that, for in-band coexistence, the telecom channels should be distributed as close as possible from the quantum channel to avoid the Raman noise peaks. Operation far from the zero dispersion wavelength of the fiber is also beneficial as it greatly reduces the generation of four-wave mixing inside the quantum channel. Furthermore, narrow spectral filtering on the quantum channels is required due to the harsh limitations of performing QKD under real telecom environments, with the quantum and several classical channels coexisting in the same ITU-T C-band.

DOI
10.1109/jlt.2014.2322108

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In this paper, we analyze the impact of the spontaneous Raman scattered noise generated from multiple optical classical channels on a single quantum key distribution channel, all within the telecom C-band. We experimentally measure the noise generated from up to 14 continuous-wave laser sources with different wavelengths using the dense wavelength division multiplexing (DWDM) standard, in both propagation directions in respect to the QKD channel, over different standard SMF-28 fiber lengths. We then simulate the expected secure key generation rate for a decoy-states-based system as a function of distance under the presence of simultaneous telecom traffic with different modulation techniques, and show a severe penalty growing with the number of classical channels present. Our results show that, for in-band coexistence, the telecom channels should be distributed as close as possible from the quantum channel to avoid the Raman noise peaks. Operation far from the zero dispersion wavelength of the fiber is also beneficial as it greatly reduces the generation of four-wave mixing inside the quantum channel. Furthermore, narrow spectral filtering on the quantum channels is required due to the harsh limitations of performing QKD under real telecom environments, with the quantum and several classical channels coexisting in the same ITU-T C-band.
In this paper we study performance of the subcarrier-wave quantum key distribution system (SCW QKD) in the presence of spontaneous Raman scattering (SpRS) noise generated by classical channels of dense wavelength division multiplexing (DWDM) network within a single-mode optical fiber. We present the mathematical model for evaluation of the quantum bit error rate (QBER) and the secure key generation rate with the SpRS noise taken into account. We consider two regimes of the SCW QKD system: the continuous wave regime that uses continuous wave laser and the pulsed regime. For these regimes, performance of the system is analyzed depending on receiver sensitivity of classical DWDM. It is found that the pulsed regime outperforms the continuous wave regime in both the secure key generation rate and the maximum achievable distance.
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 we study the performance of subcarrier-wave quantum key distribution (SCW QKD) in the presence of classical channels of optical transport network utilizing dense wavelength division multiplexing (DWDM). We consider the impact of spontaneous Raman scattering noise as well as the four-wave mixing and channel isolation efficiency. We calculate quantum bit error rate as well as the secure key generation rate of SCW-QKD protocol for different parameters of DWDM system and quantum channel allocations. Our calculations show, that quantum channel allocation at the wavelength of 1310 nm is preferable to allocation at C-band due to lower nonlinear noise, despite fiber's larger attenuation at this wavelength.
Theoretical research and numerical simulation of the noise influence caused by spontaneous Raman scattering, four-wave mixing, and linear channel cross talk on the performances of quantum key distribution (QKD) systems were conducted. Three types of QKD systems were considered: a coherent one-way QKD protocol, subcarrier-wave QKD system, and continuous-variable QKD integrated with classical dense wavelength division multiplexing (DWDM) channels. We calculate the secure key generation rate for the systems mentioned addressing different channel allocation schemes (i.e., configurations). A uniform DWDM grid is considered with a quantum channel located in the C-band and O-band (at 1310 nm) of a telecommunication window. The systems’ performances are analyzed in terms of the maximal achievable distance values. Configurations for further analysis and investigation are chosen optimally, i.e., their maximal achievable distances are the best.
Abstract Integrating quantum key distribution (QKD) into optical networks is a crucial step toward the adoption of quantum technologies in existing telecommunication fiber infrastructures. However, state-of-the-art solutions face significant challenges, including sensitivity to classical noise, particularly spontaneous Raman scattering, limited transmission distances, and varying network conditions. In this work, we present a novel discrete-variable QKD system running a time-bin BB84 protocol operating in the O-band (1295.56 nm), where the impact of dominant noise sources is effectively reduced. Combined with passive narrow-spectral filtering at the receiver, our system demonstrates robustness across diverse dense wavelength-division multiplexing scenarios, making it practical for real-world deployments. We validate its performance through extensive testing, showing stable key generation coexisting with different classical traffic conditions up to 17 dBm of total launch power. These results represent a significant advancement toward the integration of QKD into existing fiber networks, paving the way for secure quantum communication on a large scale.
Subject of study. The effect of noise resulting from spontaneous Raman scattering, four-wave mixing, and linear channel crosstalk on the performance of measurement-device-independent quantum key distribution systems with symmetric and asymmetric realizations is studied. Mathematical models of the measurement-device-independent quantum key distribution system and considered channel noise sources are presented. The secure key generation rate was calculated in all cases for assessment and subsequent analysis of the system performance. These results enabled the identification and presentation of the operation features of the measurement-device-independent quantum key distribution system upon its integration into existing fiber-optic communication networks using dense wavelength division multiplexing. Aim of the work. The performance of measurement-device-independent quantum key distribution systems integrated into fiber-optic communication lines using dense wavelength division multiplexing by means of numerical simulation is investigated. Method. An approach based on analysis of the Raman scattering cross section plot and allocation of the information channels of frequencies corresponding to areas located sideways to the pump wavelength was used to determine the optimal configurations of the allocation of quantum and information channels. A single-photon scheme in one symmetric and two asymmetric system realizations was considered for numerical simulations of the quantum key distribution system with an untrusted node. A security analysis was performed according to the Devetak–Winter bound that enables estimating the secure key generation rate in an asymptotic mode (for symmetric infinite sequences) in the presence of collective attacks in the quantum channel. Main results. It was confirmed that the implementation of measurement-device-independent quantum key distribution systems with equal paths of the sender and the receiver (i.e., symmetric) is optimal. The result deteriorated with an increase in the asymmetry parameter. If the quantum channel is within the C-band, the advantage of the symmetric realization was minimal, and it was almost indiscernible when the number of information channels was increased to 40. However, if the quantum channel was at the wavelength of 1310 nm (O band), the difference was significant. Moreover, allocation of the wavelength of 1310 nm to the quantum channel enables the longest distance of operation, and it weakly depends on the number of channels. Practical significance. For practical implementation of quantum key distribution systems, their integration into existing telecommunication infrastructure is of particular interest. This can be achieved through the simultaneous propagation of quantum and information channels in the fiber-optic communication lines by means of multiplexing, and in particular, dense wavelength division multiplexing. However, the power levels characteristic for quantum signals are significantly lower than those for information signals. Therefore, if the information and quantum channels propagate in the same fiber, the noise from the information channels significantly reduces the performance of the quantum key distribution systems. For this reason, the physical and mathematical description, analysis, and numerical simulation of the noise and its interaction with different quantum key distribution systems aimed at identifying the most effective integration method are crucial for the integration of quantum key distribution systems into existing telecommunication networks.