Figure 2
From: Quantum key distribution with hacking countermeasures and long term field trial
Schematic diagram of main components of the QKD system, showing the transmitter (Alice) and receiver (Bob). LD: Laser diode, IM: Intensity modulator, BS: Beam splitter, PBS: Polarising beam splitter, A: Variable optical attenuator, I: Optical isolator, F: Narrow band pass optical filter, DL: Delay line, MD: Monitoring detector, EPC: Electronic polarisation controller, FS: Fibre stretcher, APD: Avalanche photodiode detector, SD: self-differencing circuit.
