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Quantum Science and Technology

Noise-robust O-band quantum key distribution at 1295.56 nm for coexistence in WDM networks

Javier Núñez-Bon, Alberto Boaron, Damien Stucki, Boris A. Korzh, Rob Thew, Gianluca Boso

Published Jun 5, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1088/2058-9565/ae7826

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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.
Integrating quantum key distribution (QKD) with classical data transmission over the same fiber is crucial for scalable quantum-secured communication. However, noise from classical channels limits QKD distance. We demonstrate the longest-distance continuous-variable QKD (CV-QKD) over 120 km (20 dB loss) in the asymptotic regime, and over 100 km (17 dB loss) in the finite-size regime, both coexisting with a fully populated coarse wavelength division multiplexing system. Natural mode filtering of the local oscillator and phase noise mitigation enabled this without additional filtering or wavelength reallocation. Benchmarking against a commercial discrete-variable QKD system and considering finite-size effects confirms the feasibility of CV-QKD as a plug-and-play solution for typical 80-100 km long-haul optical networks. Our results set a record fiber distance for CV-QKD, showing its potential for cost-effective, large-scale deployment in existing network infrastructure.
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.
Abstract Integration of quantum key distribution (QKD) into existing optical transport network is one of the important problems that should be solved to expand the applicability of QKD systems and to develop quantum networks. When multiplexing a quantum channel with classical ones, researchers and engineers are faced with a high background count rate caused by spontaneous Raman scattering. This paper presents the results of Raman noise measurement in the O-band at different distances and launched power of the C-Band channels. Based on this data, the 1310 nm QKD system capable to integrate into DWDM optical network was developed. Its performance has been experimentally confirmed in testing on coexistence with intense C-band signals. The experiments were carried out on the propagation of classical and quantum signals in the same fiber as well as in the opposite directions. As a result, the stable QKD over a distance up to 60 km with a total launched power of classical channels up to 20 mW has been demonstrated.
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.
A successful commercial deployment of quantum key distribution (QKD) technologies requires integrating QKD links into existing fibers and sharing the same fiber networks with classical data traffic. To mitigate the spontaneous Raman scattering (SpRS) noise from classical data channels, several quantum/classical coexistence strategies have been developed. O-band solutions place the QKD channel in the O-band for lower SpRS noise but with the penalty of higher fiber loss and can rarely reach beyond 80 km of fiber; another method is C-band coexistence with attenuated classical channels, which sacrifices the performance of classical channels for lower SpRS noise. In this work, a time-interleaving technique is demonstrated to enable the co- propagation of quantum and classical channels in the C-band without sacrificing either performance. By embedding QKD pulses in the gaps between classical data frames, the quantum channel is isolated from SpRS noise in both wavelength and time domains. C-band co- propagation of a polarization-encoding decoy-state BB84 QKD channel with a 100 Gb/s QPSK channel is experimentally demonstrated with quantum bit error rate (QBER) of 1.12%, 2.04%, and 3.81% and secure key rates (SKR) of 39.5 kb/s, 6.35 kb/s, and 128 b/s over 20, 50, and 100 km fibers, respectively. These results were achieved with the presence of classical launch power up to 10 dBm, which is at least one order of magnitude higher than reported works. We also demonstrated the co- propagation of a QKD channel with eight classical channels with total launch power up to 18-dBm (9-dBm per channel), which is the highest power of classical channels reported in C-band coexistence works.
Quantum key distribution (QKD) provides information-theoretic security based on the laws of quantum mechanics. The desire to reduce costs and increase robustness in real-world applications has motivated the study of coexistence between QKD and intense classical data traffic in a single fiber. Previous works on coexistence in metropolitan areas have used wavelength-division multiplexing, however, coexistence in backbone fiber networks remains a great experimental challenge, as Tbps data of up to 20 dBm optical power is transferred, and much more noise is generated for QKD. Here we present for the first time, to the best of our knowledge, the integration of QKD with a commercial backbone network of 3.6 Tbps classical data at 21 dBm launch power over 66 km fiber. With 20 GHz pass-band filtering and large effective core area fibers, real-time secure key rates can reach 4.5 kbps and 5.1 kbps for co-propagation and counter-propagation at the maximum launch power, respectively. This demonstrates feasibility and represents an important step towards building a quantum network that coexists with the current backbone fiber infrastructure of classical communications.