CV-QKD in Coexistence with 1 Gb/s Classical Channel Using Electrical Frequency Division Multiplexing

Quantum key distribution (QKD) leverages the principles of quantum mechanics to enable secure secret key exchange. Continuous-variable QKD (CV-QKD), utilizing coherent states and coherent detection, has emerged as a promising method, easily integrable into existing telecom networks. In this work, we study, through numerical simulation, the coexistence of a CV-QKD channel with a classical channel capable of up to 1 Gb/s. We first analyze the performance of the quantum channel when the classical channel emits a pure tone, by varying the frequency gap between both channels and adjusting their power ratios. Then, by maintaining a fixed electrical separation of 500 MHz, we study QPSK modulation with root-raised-cosine filtering in the classical channel. In this scenario, for several signal-to-noise ratios, we reduce crosstalk by optimizing filter properties such as roll-off factor, symbol rate and number of filter taps.