Research on co-propagation of QKD and classical communication by reducing the classical optical power

He Ru-Shi^{1, 2}, Jiang Mu-Sheng^{1, 2, †}, Wang Yang^{1, 2}, Gan Ya-Hui^{1, 2}, Zhou Chun^{1, 2}, Bao Wan-Su^{1, 2, ‡}

Multiplexing schematic diagram of QKD and classical channel. The classic transmitter includes a laser, a modulator (PPM), a variable optical attenuator (VOA), and the classical receiver includes a gated APD. The duplex mode is implemented by the circulator. The QKD and classical channel are wavelength multiplexed using a DWDM.