Core and Wavelength Allocation Schemes for Noise Suppression in Quantum Key Distribution Over Multicore Fiber

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.