Fig. 1: Setup of free-space CV-QKD.
From: Free-space continuous-variable quantum key distribution under high background noise
a Top view of the experimental layout at the Guilin City of China. Alice and Bob at a distance of 860 m. b The compact modulation device for polarization encoded GMCS CV-QKD. A CW laser of 1550 nm produces a repetition rate of 10 MHz and a pulse width of 20 ns through Sagnac-1. According to the Box-Muller tansform38, the generated optical pulses are injected into Sagnac-2,3 to modulate the desired Rayleigh distribution and uniform distribution, respectively. c The transmitting antenna. A fast steering mirror (FSM) and a two-axis rotary table are used for fine and coarse tracking. A dichroic mirror (DM) is used to separate the signal and classical light. A 785 nm pulsed laser shooting from Alice to Bob for classical optical communication while also providing beam position information for fine tracking. d The receiving antenna. A similar APT system to the transmitter is implemented. A polarization analyzer consisting of QWP, HWP, and PBS is used, followed by two homodyne detectors (HOM1 and HOM2). Note LD laser diode, CIR circulator, BS beam splitter, PBS polarizing beam splitter, PM phase modulator, FR Faraday rotator, NPBS non-polarizing beam splitter, QWP quarter-wave plate, HWP half-wave plate, FSM faster steering mirror, DM dichroic mirror, IF interference filter, APD avalanche photodiode.
