The number of events of the crosstalk (points) in the quantum receiver as a function of the receiver power of the classical optical signals and the theoretical SpRS simulation (line). The classical signal and the quantum signal are multiplexed by a DWDM with 100-GHz compatible channel spacing. The red points represent the crosstalk noise of the classical signal with a frequency of 40 MHz to the quantum channel, which is detected by the SNSPD, and is consistent with the simulation. Here, β ( λ ) = 2.1 × 10 − 9 ( km · nm ) − 1 , T d = 1 × 10 − 9 s , and η d = 0.2 .