The convergence of quantum key distribution (QKD) with classical optical networks represents a pivotal advancement in secure communication technologies. This paper presents an experimental investigation of a resource allocation framework for co-transmitting QKD and classical signals through multicore fiber (MCF). We first analyze theoretical model characterizing inter-core noise interference mechanisms between classical and quantum channels over MCF. Building on this analysis, a noise-aware spatial-spectral resource allocation scheme is proposed, coordinating resources across two dimensions: core allocation via a Cartesian coordinate-based hierarchy ensures universal compatibility with arbitrary MCF configurations, while adaptive wavelength assignment dynamically suppresses single or dual noise sources. Experimental validation demonstrates the scheme's superior noise suppression capabilities and enhanced secure key rates compared to benchmark approaches, achieving reductions of ⩾ 4.2 dB in noise photons and improvements of ⩾ 10 kbps in secure key rate. This work establishes a practical foundation for implementing QKD networks within existing fiber infrastructure, advancing the realization of scalable quantum-classical coexistance.
The convergence of quantum key distribution (QKD) with classical optical networks represents a pivotal advancement in secure communication technologies. This paper presents an experimental investigation of a resource allocation framework for co-transmitting QKD and classical signals through multicore fiber (MCF). We first analyze theoretical model characterizing inter-core noise interference mechanisms between classical and quantum channels over MCF. Building on this analysis, a noise-aware spatial-spectral resource allocation scheme is proposed, coordinating resources across two dimensions: core allocation via a Cartesian coordinate-based hierarchy ensures universal compatibility with arbitrary MCF configurations, while adaptive wavelength assignment dynamically suppresses single or dual noise sources. Experimental validation demonstrates the scheme's superior noise suppression capabilities and enhanced secure key rates compared to benchmark approaches, achieving reductions of ⩾ 4.2 dB in noise photons and improvements of ⩾ 10 kbps in secure key rate. This work establishes a practical foundation for implementing QKD networks within existing fiber infrastructure, advancing the realization of scalable quantum-classical coexistance.
The integration of quantum key distribution (QKD) with classical optical networks has emerged as a pivotal strategy for building secure communication infrastructures. However, achieving their coexistence in silica-core fibers faces inherent limitations due to nonlinear interference, particularly under high classical signal power. In this paper, we experimentally demonstrate the coexistence of classical optical transport networks and QKD over 101.6 km of hollow-core fiber (HCF) with classical power exceeding 20 dBm for the first time to the best of our knowledge. Through systematic theoretical analysis, we characterize HCF’s transmission loss and nonlinear noise generation mechanisms, revealing its unique compatibility with high-power classical–quantum coexistence compared to conventional fibers. To address spectral interference from HCF’s absorption peaks and nonlinear effects, we propose a spectrally optimized multi-stage allocation (SOMA) scheme that coordinates low-loss channel selection and noise suppression. Experimental validation shows that, under the SOMA scheme, coexisting classical signals achieve 19 dBm in single-wavelength configuration and 21 dBm in multi-wavelength configuration, while maintaining a secure key rate above 10 kbps. This breakthrough establishes HCF as a viable platform for simultaneous high-capacity classical communication and quantum-secured data transmission, overcoming critical power limitations of existing fiber-based coexistence systems.
With the development of quantum key distribution (QKD), integration with classical communications has become one of the future development trends. In this paper, in order to solve the problems of fiber resource waste and noise interference in twin-field QKD (TF-QKD) where servo signals exist, we design a high-security and fiber-saving classical-quantum coexistence architecture that ensures both high security and efficient utilization of fiber resources, which is designed to be seamlessly compatible with quantum signals, servo signals of TF-QKD, and bidirectional classical signals over multicore fiber (MCF). Subsequently, an in-depth analysis of noise on the quantum channels is conducted. Furthermore, a quantum-priority core and wavelength allocation (QPCWA) scheme is proposed, which effectively reduces the noise interference from servo signals and classical signals to QKD, improving the performance of QKD. Simulation results show that the QPCWA scheme can extend the secure transmission distance up to nearly 300 km compared with the benchmark scheme. Experimental results show that the QPCWA scheme can effectively reduce noise photons by 50.8%. This research establishes a technical foundation for the integrated deployment of QKD and classical communications.
In this paper, we propose core and wavelength allocation schemes for the simultaneous transmission of classical signals and quantum key distribution (QKD) over multi-core fiber (MCF), aiming to maximize the secure key rate, and evaluate the proposed schemes in sending-or-not-sending-QKD (SNS-QKD) and Bennett-Brassard-1984-QKD (BB84-QKD). First, we formulate the noise power on quantum channels, and propose a theoretical model of backward cascaded noise of four wave mixing and inter-core crosstalk considering modulation frequency of the classical signals. Also, the impact of noises on secure key rate is calculated in SNS-QKD and BB84-QKD. Then, we propose a core allocation algorithm in order to reduce the noise interference to quantum cores, and the quantum equal frequency spacing (qEFS) and the quantum unequal frequency spacing (qUFS) wavelength allocation schemes are proposed in the same-core (SC) and the different-core (DC) distribution. Finally, we perform numerical simulation and experimental evaluation for the proposed schemes. Compared with the conventional channel allocation (CCA) scheme in SNS-QKD, the proposed schemes can extend the secure transmission distance up to 78.8%. In BB84-QKD, the secure transmission distance can be extended up to 127.1% under SC-qUFS scheme. Experimental results show that the proposed schemes can suppress noise photons up to 57.54% compared to CCA scheme.
In this paper, we investigate the impact of classical optical communications in quantum key distribution (QKD) over hollow-core fiber (HCF), multi-core fiber (MCF) and single-core fiber (SCF) and propose wavelength allocation schemes to enhance QKD performance. Firstly, we theoretically analyze noise interference in QKD over HCF, MCF and SCF, such as spontaneous Raman scattering (SpRS) and four-wave mixing (FWM). To mitigate these noise types and optimize QKD performance, we propose a joint noise suppression wavelength allocation (JSWA) scheme. FWM noise suppression wavelength allocation and Raman noise suppression wavelength allocation are also proposed for comparison. The JSWA scheme indicates a significant enhancement in extending the simultaneous transmission distance of classical signals and QKD, reaching approximately 100 km in HCF and 165 km in MCF under a classical power per channel of 10 dBm. Therefore, MCF offers a longer secure transmission distance compared with HCF when classical signals and QKD coexist in the C-band. However, when classical signals are in the C-band and QKD operates in the O-band, the performance of QKD in HCF surpasses that in MCF. This research establishes technical foundations for the design and deployment of QKD optical networks.
Quantum key distribution (QKD) is regarded as an alternative to traditional cryptography methods for securing data communication by quantum mechanics rather than computational complexity. Towards the massive deployment of QKD, embedding it with the telecommunication system is crucially important. Homogenous optical multi-core fibers (MCFs) compatible with spatial division multiplexing (SDM) are essential components for the next-generation optical communication infrastructure, which provides a big potential for co-existence of optical telecommunication systems and QKD. However, the QKD channel is extremely vulnerable due to the fact that the quantum states can be annihilated by noise during signal propagation. Thus, investigation of telecom compatibility for QKD co-existing with high-speed classical communication in SDM transmission media is needed. In this paper, we present analytical models of the noise sources in QKD links over heterogeneous MCFs. Spontaneous Raman scattering and inter-core crosstalk are experimentally characterized over spans of MCFs with different refractive index profiles, emulating shared telecom traffic conditions. Lower bounds for the secret key rates and quantum bit error rate (QBER) due to different core/wavelength allocation are obtained to validate intra- and inter-core co-existence of QKD and classical telecommunication.
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.