An Orthogonal Dual-Polarization and Time Multiplexing Scheme of Continuous-Variable Quantum Key Distribution

In this article, we propose a time and orthogonal polarization division multiplexing scheme for local local oscillator continuous-variable quantum key distribution (LLO CV-QKD) system. According to the influence mechanism of time-domain diffusion and polarization disturbance on the key parameters, such as the channel transmittance and excess noise, of the studied system, we established a dual-polarization theoretical model and verified its validity by simulations. Here, the pulse width at the nanosecond level and polarization extinction ratio (PER) are considered for optimizing the performance of secure key rate (SIKR) quantitatively. For transmitting over 25 km optical fiber, the required PER should be above 22 dB when the pulse width is fixed to lns. Moreover, the optimal repetition frequency is obtained. In this case, 5.25 Mbps SKR can be achieved under the lns pulse width and 25dB PER, considering the $10^{11}$ finite-size block. Our work provides a systematic and theoretical framework for the study of improving the SKR of the dual-polarization CV-QKD system.