Extended Data Fig. 6: Schematic of 40-MHz transceiver QKD system with a single-laser transmitter and a passive receiver.
From: An integrated space-to-ground quantum communication network over 4,600 kilometres
The transmitter and the receiver are combined in the same terminal by a channel multiplexing module including two DWDMs and a circulator. In the transmitter, the pulse generated by one laser diode first passes through an intensity modulator (IM) for decoy-state active modulation, and then a custom-made Sagnac interferometer module, which consists of a polarization-sensitive circulator (PCIR) and a phase modulator (PM) for polarization-state modulation. The polarization-sensitive circulator is an integrated micro-optical system that combines a circulator and a polarizing beam splitter (PBS), with their directions offset by 45° (inset). TIA, transimpedance amplifier; SIG, signal.
