Figure 2
From: Mutual entity authentication of quantum key distribution network system using authentication qubits
1x4 QKD network system setup for multi-user entity authentication. BS: beam splitter, Cir: circulator, APD: avalanche photo diode, DL: delay line, PBS: polarization beam splitter, PM: phase modulator, WDM: wavelength division multiplexing, QC: quantum channel, PD: photo diode, VOA: variable optical attenuator, SL: storage line, IM: intensity modulator, FM: Faraday mirror, FPGA: field programmable gate array